钙钛矿中MH曲线中的阶梯解释
Magnetization step,history-dependence,and possible spin quantum transition in Pr5/8Ca3/8MnO3
manganites
Guixin Cao,Jincang Zhang,*Shixun Cao,Chao Jing,and Xuechu Shen
Department of Physics,Shanghai University,Shanghai200436,China
?Received4August2004;revised manuscript received10November2004;published19May2005?
In order to clarify the physical mechanism of magnetization step in strong correlation manganites with a
phase separation,one Pr5/8Ca3/8MnO3single crystal was successfully grown by the optical?oating-zone
method and investigated systematically on its structural,magnetic,and transport properties.One steplike
charge ordered antiferromagnetic-ferromagnetic transition was proved below60K as an applied magnetic?eld
is only several T,and the step in the M-H curve became ultrasharp below4.2K.A history-dependent mag-
netization effect was also observed.Here,the given charge/orbital ordering and spin structure indicated that the
energy difference between ferromagnetic and charge ordering phases was small for Pr5/8Ca3/8MnO3.According
to the model of spin and orbital coupling,the steps should be the result of spin reorientation under the magnetic
?eld.Meanwhile,the two sharp step transitions appeared in the different?eld-cooled?FC?conditions at T
=2.0K,which shows a possible existence of spin quantum transition.The observed history-dependent mag-
netization re?ected the existence of d x2?y2orbital ordering state within the FM state.The correlation between
the magnetic structure and the mechanism was also discussed.
DOI:10.1103/PhysRevB.71.174414PACS number?s?:75.30.Kz,71.30.?h,71.27.?a
I.INTRODUCTION
Perovskite-type manganites with the general chemical for-mula R1?x A x MnO3?R and A being rare-and alkaline-earth ions,respectively?have been extensively researched because of their rich physical contents by various behaviors of elec-trical transport and magnetic properties,which would be very important to clarify the physical mechanism of strong correlation electron system and colossal magnetoresistance ?CMR?effect.1,2The basic microscopic picture responsible for the insulator-metal transition in the manganites has been established,which is believed to be the percolative transport through the coexistence phase of the submicrometer charge-ordered antiferromagnetic-ferromagnetic?COAFM?and FM transitions.The phase separation scenario is intrinsic in these materials and is attracting considerable attention.Neverthe-less,the physics of the CMR effect,especially the micro-scopic mechanism of the correlations among spin,charge, orbital,and lattice degrees of freedom,is far from being completely understood.Recently,several unexpected and in-triguing magnetization steps were observed for Mn-site sub-stituted manganese oxides Pr1?x Ca x Mn1?y M y O3with x?0.5, y?0.05?M is Ga,Cr,Sc,and Co,etc.?.3–5This was thought that the Mn-site substitution weakens the COAFM state and favors the development of PS,then make the required mag-netic?elds decrease.It is well known that the Mn-site sub-stitution is very ef?cient in destabilizing the strongly charge and orbital ordering.6Nevertheless,there is also the observa-tion of similar steplike transitions in Pr0.7Ca0.3MnO3and Sm0.5Sr0.5MnO3.5In these PS compounds,the magnetic?eld needed to cause the steps is only several T.Generally,via a traditional metamagnetic transition,7it will need very high magnetic?elds larger than20.0T to overcome this AFM state.Here,the lower critical magnetic?eld driven the tran-sition shows that this magnetization steps are different from the traditional antiferromagnetic transition.In addition,re-cent literature proposed that this magnetization transition is related to the martensitic character associated with the strain between the PS regions.8In the martensitic model,the COAFM and FM phases are looked upon as a high-
temperature-phase?austenite?and a low-temperature-phase ?martensite?,respectively.The step-type COAFM-FM transi-tion was driven by applied magnetic?eld when the driving
force?i.e.,the magnetic energy?overcomes the elastic energy
associated with the strains created at the COAFM/FM inter-
faces.The COAFM phase has signi?cantly larger lattice pa-
rameters and unit-cell volume than that of the ferromagnetic
phase,and the unit-cell of the antiferromagnetic?AFM?
phase is strongly distorted.As a magnetic?eld is applied in
the sample,the strains created in the AFM/FM interfaces
tend to block the development of the magnetic energy.And
when the applied?eld is suf?cient to overcome the stress
energy,the magnetization will appear a sudden increase,
which makes this martensitic transformation be discontinu-
ous with burstlike effects.In this model the effect of an ex-
ternal magnetic?eld would be only to overcome the stress
energy and promote the growth of FM phase fraction,with-
out modifying the magnetic coupling of the spins.Though
this martensitic scenario is attracting considerable attention,
the observation of sharp M-H steps in the underdoped
Pr0.7Ca0.3MnO3points towards the role of the OO/CO state,9
and such a picture did not consider the in?uence of micro-
structure on the appearance of M-H steps.Moreover,it is
dif?cult to reconcile with some experimental results that the
M-H step shows a gentle transition when above certain tem-
perature point.5In this paper,we show that the M-H steps in
PCMO are indeed far more complex than the simple marten-
sitic transition due to the sudden growth of FM phase.In-
stead,our study indicates that the M-H steps are associated
with the spin reorientation under the magnetic?eld and there
exists a possible spin quantum transition.The result chal-
lenges our present understanding the mechanism of the M
PHYSICAL REVIEW B71,174414?2005?
-H steps and suggests that,if martensitic effect plays an im-
portant role in the AFM-FM transition process,it must con-
sider the stress would in?uence the spin and orbital state of
the AFM phase fraction and its transformation under?eld
cannot be ignored for the appearance of M-H steps.
The above features prompted us to undertake a systemic
study about this peculiar COAFM-FM transition.In this
work,the Mn-doping free Pr5/8Ca3/8MnO3?PCMO?single crystal was used to study this dreamscape magnetization.
Based on its coexistence characteristics of FM,AFM,and
CO phase at low temperature,it should be reasonable to
predict that the unusual steps in magnetization and related
properties might be observed in PCMO as an applied mag-
netic?eld change.The structural,magnetic and transport
properties of single-crystal PCMO were investigated.The
COAFM-FM step transition is found in the M-H curve be-
low60K as the applied magnetic?eld is only several tesla,
and the step becomes ultrasharp below4.2K.The two simi-
lar sharp step transitions in the different FC conditions and
the history-dependent magnetization effects were also ob-served.This kind of step transition should be the result of spin reorientation under the magnetic?eld and there exists a possible spin quantum transition.Above10.0K,however, the step was not sharp,which was caused by the effect of thermal?uctuations that smears the transition and affects the ?uctuation rate of orbital.The related mechanism and pos-sible interpretations were also discussed.
II.EXPERIMENTAL DETAILS
A single crystal of Pr5/8Ca3/8MnO3?PCMO?with a size of 32mm in length and4mm in diameter was grown by optical ?oating-zone method in a?owing O2atmosphere ?100cc/min?at a rate of2mm/h.The rod was cut and two slices were obtained with a size of0.5mm thick along lon-gitudinal and transversal section,respectively.Then they were polished for microstructural analysis.X-ray-diffraction measurement revealed a good single-phase structure and showed that the longitudinal section of the slices is in the a-b plane and the transversal section is along the c axis. Low-temperature x-ray-diffraction data for single crystal PCMO were obtained by18kW D/max-2550using Cu-K?radiation in the range of300–10K.Magnetic measurements were carried out using PPMS-9?physical property measure-ment system,Q/D Inc.,US?with the precision20nV for voltage,and0.2Oe for the magnetic?eld.All the M-H curves were recorded after the sample was cooled under zero-?eld cooling?ZFC?or?eld cooling?FC?condition from the paramagnetic state at300K.Resistivity measurements were carried out using the conventional four-probe tech-nique.The resistivity vs temperature?-T curves measured under applied dc magnetic?elds ranges from0–6.0T were recorded by PPMS in the range of1.9–300K with a tem-perature precision of0.01K.The experiment results are re-peatable.
III.RESULTS AND DISCUSSION
A.Transport characteristics,structure,and orbital ordering
Figure1showed the temperature dependence of resistiv-ity for cooling and heating conditions at the applied magnetic
?elds of0.0,3.0,and6.0T,respectively.It can be seen that
both the curves under zero?eld and3.0T have a semicon-
ducting behavior and superposed for the same?eld during
cooling and heating.On the other hand,these?-T curves show a superposition above230K and a discernible upturn
around230K,which corresponds to the onset of CO.10Ac-
cording to Asaka’s work,the present onset has con?rmed the
existence of superlattice structure below230K for PCMO as
a further evidence of the d3x2?r2/d3y2?r2-type charge/orbital ordering by low-temperature transmission electron
microscopy.11An applied magnetic?eld of6.0T drastically
modi?es such an insulating CO state and the?-T curve un-dergoes a I-M transition at T p?84K?peak value?for the cooling curve and T p?110K for the heating curve.This shows that the transition becomes strongly hysteretic and the
?rst-order transition exists in the present system.However,it
must be noted that the low-temperature resistivity below T p ?28Ohm cm?is larger than the Mott’s maximum metallic limit.Figure2shows the temperature dependence of the M-T curve measured on heating for ZFC and FC in a?eld of 6.0T.The inset displays resistivity curves recorded under the same conditions.The M-T curves display the same gen-eral features as the similar compounds?0.3?x?0.4?:11,12?i?two kinks correspond to the CO temperature T CO and Nèel temperature T N around230and160K,respectively;?ii?at low temperature,magnetization M appears an large increase at about70K for the cooling curve and102K for the heat-ing curve,respectively.If associating these temperatures with the onset of FM ordering,we can?nd that the I-M transition temperature,as shown in Fig.1and in the inset of Fig.2,is higher than T C,which probably shows that the true T C in the system is considerably higher than observed in the present experiment.Below about100K,the ZFC and FC curves separate from each other when approaching the phase separation region.This feature displays the?rst order char-acteristics of this ferromagnetic transition.Meanwhile,it suggests that both magnetization and resistivity are related to dependence on the magnetic history as shown in Sec.III C. This further indicates that it is not induced by the transition FIG.1.?Color online?The temperature dependence of resistivity under0,3.0,and6.0T for Pr5/8Ca3/8MnO3.The resistivity was measured in FC mode.Inset gives the magni?ed curves of?-T under6T at below20K,which shows a distinct minimum in the vicinity of13K.
CAO et al.PHYSICAL REVIEW B71,174414?2005?
from an orbital ordering ?OO ?to an orbital liquid by enough magnetic ?elds but did from one type of OO to another OO.Another prominent feature of the ZFC curve is that there is a steep rise in the M -T curve as the temperature increases be-tween 4and 12K,and M is nearly invariable between 1.9and 4K.According to the intrinsic COAFM phase coexists with FM phase at low temperature,such behaviors could connect with the increase of the FM phase at the expense of the AFM phase fraction,which shows the temperature de-pendence of the COAFM-FM coexistent phase.In addition,it should be noted that the difference between the values of the magnetization M for the ZFC and FC curves around 110K might be related to the large magnetostriction pres-ence in this material.13The ?-T curves recorded in the ZFC and FC modes split near T =130K,as M -T curves did.In the low-temperature region ?T ?100K ?,?-T and M -T curves vary exactly in opposite ways,which is qualitatively consis-tent with what the double exchange ?DE ?model predicts.This behavior could be more dif?cult to understand for Pr 1?x Ca x MnO 3?Ref.14?with a smaller one-electron band-width W of the e g electrons.In the case,it can be only con-jectured that the COAFM state was changed to FM metallic state under the suf?cient magnetic ?eld.That is,the CO was melted and the spin was realigned towards FM behavior.And the spin and OO are strongly coupled with each other.15As a result,it can be supposed that in this case,magnetic ?eld can affect the d 3x 2?r 2/d 3y 2?r 2-type OO and modulate the spin structure accordingly,and then favor the transformation of AFM phase.Experimentally,it has been observed that the e g electron preferred to occupy the d x 2?y 2orbital under magnetic ?eld.16According to the DE model,17,18if the localized t 2g spins are considered classically,the transfer integral t of e g electrons between Mn 3+?t 2g 3e g 1?and Mn 4+?t 2g 3e g 0?ions can be expressed as 19
t =t 0cos ??/2??t 0??1+m ?/2,
?1?
where t 0is the transfer integral in a fully spin-polarized state,m is the normalized magnetization,and ?is the angle be-
tween nearest-neighbor spins.The normalized magnetization m depends on temperature according to the following self-consistent equation:20
m =B S ??m ?,
with ?=
3S 1+S T C
T
,
?2?
where
B S ?x ?=
2S +12S cth ?2S +12S x ??12S cth ?12S
x ?
?3?
denotes the Brillouin function with S =2?x /2=1.8152;In order to analyze the effect of temperature on t ,we can ?rst ?t the m at Curie temperature T C =70K in terms of Eqs.?2?and ?3?,in which the T C value is taken from the FC magnetiza-tion result at 6.0T as displayed in Fig.2.The ?tted m value is quite coincident with the experimental result for the curve T ?T C .as shown in the inset of Fig.2.That is to say,the trend of the curve of t was consistent with the FC magneti-zation result for T ?T C .However,for T ?T C ,the change of T N and T CO is not re?ected in the ?tted curve.Nevertheless,both the theoretically ?tted curves and experimental results coincide each other for T ?T C ,which shows the existence of orbital polaron.20This is consistent with the result ?-T at low temperature as displayed in the inset of Fig.1,which gives a distinct minimum in the vicinity of 13K.The resis-tivity minimum is probably due to the carries localization induced by orbital polarization.Both those re?ect the effect of orbital on the transport behaviors,and the effect of spin on the process needs further investigation.Under this case,the appearance of orbital state indicates that the behavior of ?-T and M -T for PCMO should have an anisotropic charac-teristic.According to the DE mechanism,the system should show an isotropic behavior by gaining a maximum kinetic energy and has no OO state in the FM metallic state.How-ever,experimental and theoretical results have revealed a complex phase diagram that is certainly beyond the DE ideas,so Jahn-Teller ?JT ?distortions and orbital order are also needed to understand the physical picture of manganites.Indeed,the d x 2?y 2-type orbital ordering was observed in the FM state of 50%hole-doped Pr 1/2Sr 1/2MnO 3and Nd 1/2Sr 1/2MnO 3.21There are theoretical results that simu-lated the existence of OO in the FM state.22So,in the present case,we suggest both the magnetic and electrical transport properties at low-temperature region ?T ?100K ?should have probably the two-dimensional character due to the ex-istence of d x 2?y 2OO state.In addition,it must be noted that the role of spin and orbital on the electrical transport process can be checked at low temperature,since the electrical and magnetic transport properties is correlated with each other.Resistivity versus temperature for different magnetic ?eld should be carried out to investigate detailed the low-temperature resistivity minima as shown in the inset of Fig.1.The relevant ?tted work should be carried out according to ??T ?=1/???0?+AT 1/2?+BT 9/2+CT n ,where ??0?is the re-sidual conductivity and A ,B ,and C are all constants.1/??0?+AT 1/2denotes electron-electron ?e -e ?interaction,BT 9/2denotes DE contribution,and CT n denotes additional inelastic contributions.Meanwhile,the resistivity versus
T
FIG. 2.?Color online ?dc magnetization curves of
Pr 5/8Ca 3/8MnO 3in a applied ?eld of 6.0T.The black and red sym-bols correspond to the ZFC and FC modes,respectively.Inset in the top right corner displays resistivity curves recorded in the same conditions,and in the down left corner is the transfer amplitude t as a function of temperature ?black and red symbols stand for experi-mental and ?tted curves,respectively ?.
MAGNETIZATION STEP,HISTORY-DEPENDENCE,AND …PHYSICAL REVIEW B 71,174414?2005?
under variational magnetic ?eld can also study the spin-orbital scattering contribution if the negative magnetocon-ductance appears.
It is well known that the setting of the CO in manganites can result in signi?cant distortions of the unite cell.This originates from cooperative Jahn-Teller effects and is accom-panied by orbital ordering.23Recently,the presence of struc-tural anomalies between T C and T N ,which is related to the development of a strong JT-type distortion with decreasing temperature,have reported by Cox et al.24In their work,for PCMO,observed phenomena proved that there exist the change of CO and OO as the temperature or the magnetic ?eld vary.In order to study in detail the possible structural distortions as temperature decreases due to CO/OO,we stud-ied the temperature dependence of the lattice parameters and the unit cell volume as shown in Fig.3.The lattice param-eters are calculated based on least square ?tting.It can be seen that their behavior is in qualitative agreement with pre-viously published data on similar compounds.25The com-pound has a Pbnm orthorhombic perovskite structure,11which is evidenced by the decrease of both the lattice param-eter b and the unit-cell volume with decreasing temperature near the room temperature.It does be an O ?structure with b /?2?a ?c in the range of the measured temperature.To the low temperature behavior,a number of changes on the lattice parameters are correlated to the characteristic of struc-tural and magnetic ordering temperature T CO ,T N ,and T C ,respectively.CO/OO are related to the crystal and spin struc-ture,and OO is expected to produce a signi?cant change of the crystal structure and the anisotropy of the spin exchange.As the d 3z 2?r 2ordering,for example,the out-of-plane lattice constant c becomes bigger than the in-plane lattice constants a and b ,and the exchange interaction along the c axis will be stronger than that within the a -b plane.As Fig.3displayed,the lattice parameters display some changes in the region between T CO and T N ,with a drastic increase of b and faintly increase of a after T CO ,which indicate the occupancy of the d 3x 2?r 2/d 3y 2?r 2orbital when T ?230K.However,when tem-perature is below T N ,a and b decrease and c slightly in-creases,which shows the d 3z 2?r 2orbital of e g electron begins to be occupied.The present observations are in good agree-
ment with the proposed model for the PCMO superstructure by Asaka et al.,11except that present results show the d 3x 2?r 2/d 3y 2?r 2orbital should be a long-range ordering when below T CO ,though it is not observed by the electron diffrac-tion.Here,the obscure decrease of c should be noticed be-tween T CO and T C ,possibly because the orbital ordering of Mn 3+in the a -c plane is mostly compensated for the disor-dering of the d 3z 2?r 2orbital along c axis.That is said that,according to the results of low-temperature XRD,above T CO the e g electrons randomly distribute in Mn sites,and below T CO there appears d 3x 2?r 2/d 3y 2?r 2ordering within the a -b plane,while along the c axis d 3z 2?r 2is completely disordered.Only when the temperature is below T N ,does the extra Mn 3+e g electron begin to occupy the d 3z 2?r 2orbital.In terms of earlier neutron-diffraction result,26the extra electron intro-duced into the structure due to the x concentration changing can modulate the “robustness”of the CO state.Accordingly,the AFM spin structure of the system is also modi?ed,and that it will affect the collapse of the CO domains.In Pr 1?x Ca x MnO 3compounds with x ?0.5,the CO regions is more “harder,”and with deviation of x from 0.5,the spin arrangement along the c direction will change and make the CO regions become more “soften.”From this point of view,the spin and orbital structure can determine the required criti-cal magnetic ?eld to melt the COAFM phase.
B.Magnetization step and orbital/spin structure
ac magnetic susceptibility measurements have been widely used to characterize magnetic transitions occurring in CMR materials,especially in the PS manganites.27,28Figure 4gives the results of ac magnetic susceptibility and the ?eld dependence of magnetization at selected temperatures in
ac
FIG.3.?Color online ?Lattice parameters and unit cell volume as a function of temperature for Pr 5/8Ca 3/8MnO 3
sample.
FIG.4.Results of the ac magnetic susceptibility measurement and the magnetization isotherms at selected temperature to be cor-responding to the results of ac susceptibility curve.Which is labled with ?a ??300K ?,?b ??230K ?,?c ??148K ?,?d ??60K ?,?e ??30K ?,?f ??15K ?,?g ??10K ?,?h ??4.2K ?,and ?i ??2K ?,respectively.
CAO et al.PHYSICAL REVIEW B 71,174414?2005?
susceptibility curves.For the present measurement,the low ac magnetic?eld?H ac=10Oe ?is not supposed to affect the magnetic state of the sample.From these results,it can be seen that there are two kinks around240and160K corre-sponding to the CO temperature?T CO?and Nèel temperature ?T N?,respectively,which is consistent with above electronic and magnetic results.According to the kinks in the M?-T
curve,there exist many kinds of magnetic structure as the temperature varies in PCMO.Some representative tempera-are selected which is labeled with?a??300K?,?b?
??148K?,?d??60K?,?e??30K?,?f??15K?,?g?
?4.2K?,and?i??2K?,respectively,and corre-
M-H curves are measured as shown in Fig.
For each measurement,the sample was cooled un-der zero-?eld from room temperature to the selected tem-
perature,M-H curves were measured in a cycle sweeping mode?0→7.0T→0→?7.0T→0?with a sweeping rate of 60.0Oe per s.It can be seen that the M at300,230,and 148K increases linearly in proportion to the applied?eld until7.0T.On the whole,the slope of M-H curve is related to the magnetization value at selected temperature point as shown in the ac susceptibility curve.There is a little decrease of the M-H curve slope for148K comparing with230K.It should be noticed that temperature point?b?,T=230K,lies below the CO transition T CO near and point?c?,T=148K, below the AFM transition T N about.From increasing slope for M-H curve,it shows that magnetic order is stronger in CO phase than in AFM state.This indicates that the change of magnetization under magnetic?eld should be related to the orbital polaron.20For the M-H curve below60K,an initial magnetization increases linearly with H,which indi-cates the AFM phase domains at the low?eld.At a critical magnetic?eld H,a?eld-induced step occurs,associating with the transition of COAFM phase fraction to FM state. The magnetization reaches almost a saturation moment of 3.45?B/f.u.at7.0T,which is consistent with the expected value for Pr5/8Ca3/8MnO3in theory and this highly magne-tized state can be regarded as a fully spin-polarized phase.As we have seen in Figs.4?d?,4?e?,4?f?,and4?g?,the transition from AFM to FM state shows a gradual character.However, this behavior changes dramatically below4.2K as shown in Figs.4?h?and4?i?,which shows an abrupt step near H c =5.5and5.8T for T=4.2and2K,respectively.Their width are smaller than1?10?4T.In the frame of martensitic sce-nario,the strains created at the AFM/FM interfaces tend to block the development of the magnetic energy.And when the applied magnetic?led is suf?cient to overcome the stress energy,the magnetization will appear a sudden increase.This is consistent with the appearance of abrupt M-H steps below 4.2K.While for the gentle step above10K,according to the phase separation model,it seems to suggest a process during which the critical magnetic?eld drives this transition in dif-ferent parts of the sample.Why they behave different trans-formation process for the temperature below 4.2K and above10K?Both models did not give satisfactory explana-tion.Actually,the sharp step appeared below4.2K and fairly weak critical?elds?only?6.0T at2K?,as shown in the isothermal magnetization curves in Fig.4,would not be un-derstood only based on simply competition between the FM and COAFM.If the steps originate from equally strong and competing AFM and FM exchange interaction,spin?uctua-tions would inevitably be enhanced in the boundary of FM clusters and COAFM,and smear the transition.In addition, both models give only a mesoscopic picture to the magneti-zation transitions because of the mesoscopic phase coexist-ence of COAFM and FM fractions.In terms of the result of Figs.1and2,we have displayed the contribution of orbital state to the transport process,which shows that applied mag-netic?eld not only acts on the spin of AFM phase fraction, but also can induce the variety of orbital.The anisotropic AFM ordering of spins in the sample as shown in Fig.5is one of the manifestation of the coupling between spins and orbitals.23,26,29Moreover,the critical?eld driving the steps is remarkably small?Fig.4?,which is consistent with mean-?eld and numerical relaxation analysis14and further indi-cates the steps are closely related to the spin and charge structure.All these?ndings thus favor a drastic change of the microscopic spin orientation at the M-H steps.Indeed,using the numerical simulation results according to coupling be-tween spin and orbital degree of freedom,15Koshibae et al.?nd a charasteristic magnetization process of manganites. Based on the data above,we conjecture a scenario in which the occurrence of M-H steps is due to a microscopic spin reorientation of the AFM phase due to the change of OO with the magnetic?eld.As for the steps of M-H above10K, which becomes a gentle slop,it is the effect of thermal?uc-tuations that smears the transition.The suppose is accordant with the model of spin and orbital coupling of Koshibae et al.,which think that the recovering of spin ordering depends strongly on the state of orbital in the e g state of Mn ions.In other words,the spin moment is accompanied with the change of the orbital structure and?nally results in a mag-netization process of manganites,which shows only a typical phenomenon of the stabilization of speci?c spin values.
For a Pr1?x Ca x MnO3system,the effective hopping of e g, i.e.,the kinetic energy of e g electron can be given as
H?t=t0?
?ij????
t ij??c?i??
+c?
j??
++H.c.,?4?
where c?i???c?i??+?denotes the annihilation?creation?operator with spin?in the?orbital on site i with the constraint.t ij??FIG.5.?Color online?The charge/orbital ordering and magnetic structure of Pr5/8Ca3/8MnO3at low temperature.
MAGNETIZATION STEP,HISTORY-DEPENDENCE,AND…PHYSICAL REVIEW B71,174414?2005?
is a hopping integral between?orbital on site i and?orbital on site j.When an external magnetic?eld is applied in the z direction,the Zeeman term can be introduced,
H Z=?2?B H?i?S i zt2g+S i z?.?5?For PCMO,in the COAFM phase,the Hund coupling to-gether with kinetic energy as shown in Eq.?4?,can induce an effective ferromagnetic interaction between the sites occu-pied and unoccupied by an e g electron.The spin state can be easily modi?ed by the magnetic?eld due to the suppression
of AFM interaction J t
2g by the effective FM interaction.
Therefore the ordering of spin and orbital of ground state is determined self-consistently.Finally,when magnetic?eld is applied,the spin was modulated by orbital and the step ap-pears,which is consistent with the results in Fig.4.
The structure of PCMO and the correlation of CO/OO
with spin mode as the applied magnetic?eld varies can be
illustrated by the charge/orbital ordering and magnetic struc-
ture of PCMO at low temperature as shown in Fig.5.Just
contrary to the“x=1/2plus defects”scenario due to x away
from0.5,there is no defect to be constructed into the speci?c
charge arrangements.Because,for Pr5/8Ca3/8MnO3,the ratio
of Mn3+to Mn4+in the sublattice is5:3according to the
chemical composition,except that the alternation of?3x2?r2?and?3y2?r2?orbital appears in the a-b planes,and the extra e g electrons occupy3d z2?r2orbital on the Mn4+sublat-tice which is along the c direction instead of parallel to the
a-b layers.24This charge/orbital pattern is consistent with our
XRD results.It should be noted that the Coulomb interaction
in this charge state is lowest and plays an important role in
the observed CO phase.9,30The magnetic structure at low
temperature as shown in Fig.5is commonly described as the
pseudo-CE type for Pr5/8Ca3/8MnO3.14,26,31The spin ordering
arrangement is a single FM zigzag chain with alternating
Mn3+and Mn4+ions along the corner sites.However,all the
neighboring chains will exhibit ferromagnetic ordering ex-
cept that the?3z2?r2?orbital is occupied.Along the c axis, the neighboring a-b planes stack with no change and the AFM Mn-O layers are ferromagnetic coupled.The observa-tion will essentially mean that an electron passes a corner site of the zigzag chain and acquires a phase that depends on the orbital through it passes.This can lead to an effective dimer-ization that splits the bands and open a gap at the Fermi surface.32Maybe,the gap can determine the value of critical magnetic?eld H C of the step occurrence.
The effective ferromagnetic interaction depends on which
orbital is occupied by an e g electron.So,the different orbital
case in the ground state will make the spin structure have
different change with increasing magnetic?eld.According to
the CO/OO and spin structure in Fig.5,the magnitude of the
effective FM interaction?J34?for Pr5/8Ca3/8MnO3is nearly zero,which is an average result based on different orbital occupied.So the relative spin structure can change into com-plete FM state at a certain magnetic?eld without intermedi-ate phase transition.This should be the reason that only one step occurs.It must be pointed out that the complete FM state after steps should be an orbital liquid state with random orbital disorder.In fact,in terms of this explanation,the M-H step should behave sharply.However,it can be found from Fig.4that between60and10K,with the increase of magnetic?eld,the step shows a gentle slop,while it dose not display a sharp step transition as it does below4.2K.From the numerical results about the coupling between the spin and orbital degrees of freedom,15it can be concluded that the magnetization process is not scaled by only J t
2g
,but is deter-mined by the balance of magnitude between J t
2g
and the effective FM interaction caused by t0and the Hund coupling. For the experimental results between60and10K in Fig.4, this magnetization process can be attributed to the ratio of J t
2g
/t0.Here,J t
2g
is temperature dependent.As the tempera-ture increases,the effective FM interaction is suppressed due to the thermal?uctuation.Therefore,J t
2g
/t0is larger above 10K than that below4.2K,so the step becomes more gentle slop when temperature is above10K.The results can also be understood according to the change of t as temperature de-creases.From inset of Fig.2,we can?nd t becomes bigger after T?T C,so this can possibly explain why the M-H steps are easy to appear under only several T.According to the orbital polaron theory,20the?uctuation rate of orbital is?xt: the stronger the orbital?uctuates,the more its stabilization is unfavorable.Then,the large?uctuation rate of orbital will make easily the corresponding spin orientation,i.e.,it will need less energy to cause the occurrence of steps below 60K.As for the difference above10K and below4.2K,it is because the thermal?uctuation affects the?uctuation rate of orbital above10K and the COAFM-FM step is not sharp.
It is more interesting that two sharp steps appear for PCMO system in the different FC conditions at T=2.0K as shown in Fig.6.All these FC magnetization curves are ob-tained with?eld cooled from300K,and after stabilization at the measurement temperature2K,the?eld was reduced to zero,and then M-H was measured in a?eld sweeping mode ?0→7.0T→0→?7.0T→0?.Surprisingly,the?eld cooled M-H in magnetic?eld2.0,3.0,and4.0T are nearly the same,and there are all two jumps occurred near the same critical?elds.Only when the sample is cooled in a suf?cient high magnetic?eld6.0T,does the M-H curve display an FIG.6.?Color online?M-H curves at T=2K after cooling in different positive?elds.
CAO et al.PHYSICAL REVIEW B71,174414?2005?
almost fully ferromagnetic state and eliminate the steps.But the twofold step is dif?cult to be accounted for merely by the martensitic mechanism.In the frame of martensitic model,6 the occurrence of multisteps on M-H curves is such that: When the?eld value is high enough to locally overcome the stress constraints,it will trigger a sudden motion of FM/ COAFM interfaces in a part of the sample and then induce a abrupt increase of the magnetization.Along this process,the magnetic energy decrease and the stress energy increase, which can lead the system to be frozen in another metastable balance state.Then,the overall transition may appear succes-sive steps on the M-H curves.However,according to the result of low-temperature XRD as displayed in Fig.3,the low-temperature CO phase is long-range ordered in the sample.Though the XRD experiment shows no trace of FM phase in the sample it should be understandable in terms of a long-range-ordered characteristic.33Since there exists a bal-ance between long-range-ordered FM and COAFM phases in the sample,the magnetic energy is only needed to overcome one type of stress energy created at the COAFM/FM inter-
faces.Because applied magnetic?eld should be simulta-neously acts on the whole sample uniform.Then it will be only one step appears with magnetic?eld increasing.The appearance of similar twofold steps at different FC condi-tions is dif?cult to understand according to the simple mar-tensitic transition.The present FC twofold step phenomena prove the existence of the spin quantum phase transition due to the interplay of spin and orbital orderings,which should re?ect an intrinsic property in the strong correlation manga-nite systems.FC may stabilize certain types of spin structure and accordingly the orbital structure also changes with the spin structure.So the effective FM interaction J34will have a certain value.That is to say,FC can modulate the orbital ordering state of Pr5/8Ca3/8MnO3,and when the M-H begins to be measured under magnetic?eld,the orbitals can gain energy through the J34term.Thus,as the magnetic?eld in-creases,a certain type of spin and orbital state will be stabi-lized in the intermediate process.In Fig.6,it shows that the FC curves at2.0,3.0,and4.0T are similar,which indicate that they should stabilize the same type of spin structure during the cooling process.Then,with increasing magnetic ?eld,the state with certain magnetization value?here is about3.2?B/f.u.?appears.The corresponding orbital struc-ture also changes with the spin structure.We suppose that there is possible presence of d x2?y2orbital ordering at the intermediate spin state just on the second step boundary, which increases the transfer integral t of the e g electrons and the FM interaction.The character of the preferred e g state under magnetic?eld is similar to that of La1?x Sr x MnO3.16 Meanwhile,it should be noted that the coupling constant of spin and orbital is anisotropic due to the dependence on hop-ping integral t ij ab.If we chose the orbital basis as a,b ???3z2?r2?,?x2?y2??,the transfer matrices will be denoted as
t x/y ab=t?1/4??3/4
??3/43/4
?and t z ab=t?1000?,?6?
which indicate that the orientation at a given bond can deter-mine the transfer amplitude,and consequently affect the spin orientation of the system.With further increasing magnetic ?eld,the perfect FM state with orbital degeneracy appears. Therefore,since the ordering of spin and orbital is deter-mined self-consistently,the quantum phase transition of magnetization is history dependent on the spin and orbital structure.According to our explanations,it must be empha-sized that the value of critical?eld,which drives the COAFM-FM transition,should be given by the spin and or-bital structure,i.e.,the robustness of the CO phase in the PS system.Therefore,they must be well reproducible and inde-pendent of the relative fraction of two phases.The property will be easy to be proved using additional thermal treatments to a ceramic sample since the phase separation can be con-trolled by the grain boundaries,34the chemical pressure,and oxygen-isotope composition.1
In addition to the?eld-induced magnetization steps,the experimental data in Fig.4also convey the character of the thermal effect,for which the M-H curve depended strongly on temperature.For the M-H curve below60K,the critical magnetic?eld of the transition of COAFM to FM state,i.e., the critical?eld induced the appearance of step,can be de-?ned as H C A-F.For the measurement process from7.0to0T, the M-H at30and60K remains in FM behavior initially and then appears a FM-AFM transition at critical magnetic ?eld,which can be de?ned as H C F-A.For the M-H curves measured below?10K,however,a typical long-range fer-romagnetic behavior appears.From the experimental data, we give the magnetic transition phase diagram at low tem-perature in Fig.7.Here,a hatched area shows a hysteretic region,which is the characteristics of?rst order phase tran-sition and displays a bistable region where the COAFM and FM state can coexist.Meanwhile,the present phenomena also show that magnetic?eld can induce the appearance of PS state in the system.The hysteretic region depends criti-cally on temperature and becomes broader as temperature decreases,which is due to the suppression of the effect of thermal?uctuation on the phase transition boundary.And this is thought to be a generic feature of the?rst order phase transition at low temperature.35From Fig.7,we can also
see FIG.7.?Color online?Magnetic phase diagram for Pr5/8Ca3/8MnO3against an external critical magnetic?eld.Open and closed circles represent the H C A-F and H C F-A,respectively.AFMI and FMM stand for antiferromagnetic insulator and ferromagnetic metal,respectively.
MAGNETIZATION STEP,HISTORY-DEPENDENCE,AND…PHYSICAL REVIEW B71,174414?2005?
that both the critical magnetic ?eld H C A -F and H C F -A
are func-tion of temperature below 60K.The critical ?eld to destroy the CO state enhances with the increase of temperature in the low-temperature region,which is similar to the relative ex-periment results for x =0.5and is inconsistent with x =0.35
and 0.40.36It is also clear that H C
A -F
in Pr 5/8Ca 3/8MnO 3below and above ?20K are different,even though the applied magnetic ?eld at or above H c is required to overcome the energy barrier between AFM and FM under isothermal con-ditions.The energy barrier determines the value of critical
magnetic ?eld at a ?nite temperature.Below ?20K,H C A -F
increases with decreasing temperature because the thermal ?uctuations of the localized magnetic moments and/or elas-ticity of the lattice in the AFM state are reduced,thus en-hancing the negative exchange interaction.The increased negative exchange interaction raises the energy barrier be-tween AFM and FM state,and the larger H C
A -F
is needed to accomplish the transition.Since the formation of the FM is accompanied by a contract of the crystal structure,24this re-sults in the dominating positive exchange interaction and thermal ?uctuation at low temperature is not strong enough to destroy the FM state in Pr 5/8Ca 3/8MnO 3.Therefore,the AFM-FM transition is irreversible below ?20K.On the other hand,the free energy difference between AFM and FM state also increases with temperature above 20K,and so does the critical magnetic ?eld.This increase may be asso-ciated with the thermal expansion of the Pr 5/8Ca 3/8MnO 3crystal lattice,for which the small changes in interatomic distances may have a pronounced effect on the free energies
of the AFM and FM states.37However,H C A -F
increases all along with the temperature increasing above ?20K,which is likely caused by the increased thermal ?uctuation and/or thermal expansion of the lattice and then increases the en-ergy barrier of the AFM and FM state in the Pr 5/8Ca 3/8MnO 3system.
C.Metastable magnetic order and history-dependent
magnetization
In order to study the low-temperature properties in more detail,we performed the measurements of M -H by two suc-cessive sweeping cycling of magnetic ?eld at 15K and 2K,respectively.The relevant results are given in Fig.8.Samples were zero-?eld cooled before a magnetic ?eld was increased according to the cycling of two continuous 0→7.0T →0
→?7.0T →0sweeping process.From Fig.8,it can be found that for the M -H curve measured at T =15K there exists a nearly rectangular loop and the virgin curve itself lies outside of this loop.Here,no hysteresis is observed for https://www.wendangku.net/doc/bc3019746.html,pared to the curve at 15K,the loop of virgin curve at 2K is sharper,and the curve of the second cycle displays FM state even at the beginning measurement of the second cycling.This phenomenon shows that the FM part is history dependent and has also the character of memory ef-fect.Only by heating the sample above 160K,could the sample recover its original state,which shows that it is highly temperature sensitive.On the other hand,at low tem-perature the resistivity decreases to 10?4magnitudes on an applied ?eld of 6.0T as shown in Fig.1.The resistivity and magnetization of ZFC and FC processes are very different ?see Fig.2?.All these results indicate the existence of the metastable magnetic ordering,which is possibly caused by a ?eld-induced change in the orbital occupancy of e g electron.38,39Meanwhile,a large magnetostriction appears in the magnetization process due to the magnetic ?eld.15The mechanism of magnetostriction is originated from the inter-change coupling of magnetic moment of atoms.In terms of the charge,orbital and spin ordering structure at low tem-perature for Pr 5/8Ca 3/8MnO 3as shown in Fig.5,the magne-tostriction under the applied ?eld may improve the orbital overlap within the plane and enhance the probability of the charge transfer.Actually,the wave function of d x 2?y 2stretches along the x axis and y axis,then the distance be-tween 3d and O 2?along the same axis becomes larger than that along z axis,which will induce the lower free energy and the system is more stable.These phenomena mean the possible presence of d x 2?y 2orbital ordering and thus increase the transfer integral t of the e g electrons and increase the FM interaction.The characteristics above are consistent with the steps of M -H due to the interplay of spin and orbital.The appearance of second curve within the virgin curve is be-cause of the history of spin and orbital structure.In this sense,the present history-dependent magnetization is related to the orbital structure.A situation with the spins standing perpendicular on the orbitals rather than pointing in the or-bital plane seems to be energetically preferred.
IV .CONCLUSIONS
In order to clarify the physical mechanism of magnetiza-tion step in strong correlation manganites with phase separa-tion,the Pr 5/8Ca 3/8MnO 3single crystal was successfully grown by the optical ?oating-zone method and investigated systematically on the structural,magnetic,and transport properties.Theoretically,the destruction of the orbital order-ing by an external ?eld gives rise to the structural phase transition and the recovering of the DE,which promotes the polarization of the t 2g spins.In the present case,the ?eld-induced magnetostriction occurs and indicates orbital occu-pancy of the e g electron of the Mn 3+change with the mag-netic ?led.And then this orbital occupancy causes the occurrence of the M -H step and the history-dependent mag-netization effect.The step becomes ultrasharp below 4.2
K.
FIG.8.M -H curves were measured by two successive sweeping cycling of magnetic ?eld at 15and 2K,respectively.
CAO et al.PHYSICAL REVIEW B 71,174414?2005?
In the FC conditions,the two sharp steps appear at T=2K, which shows a possible existence of spin quantum transition. The results proved that all the magnetization steps and history-dependent magnetization effects were related to the interplay of spin and orbital degrees of freedom,indicating the presence of a?eld-induced change in the orbital occu-pancy of the e g electron of the Mn3+,which shows the pos-sible appearance of d x2?y2orbital ordering.On the other hand,the directional dependence of the spin and OO corre-lations was clearly observed in the FC M-H measurement, which further makes sure the fact that the spin?uctuations are driven by the speci?c d x2?y2-type orbital ordering in the intermediate step process.
ACKNOWLEDGMENTS
This work is supported by the National Foundation of National Science of China?Grant No.10274049?,The Key-project of the Science&Technology Committee of Shanghai Municipality?Grant No.04JC14039?,Down Project of the Education Committee of Shanghai Municipality?Grant No. 03SG35?and the Key Subject of Shanghai Educational Com-mittee.
*Email address:jczhang@https://www.wendangku.net/doc/bc3019746.html,
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关于菲利普斯曲线的知识
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11、任何人都应该有自尊心、自信心、独立性，不然就是奴才。但自尊不是轻人，自信不是自满，独立不是弧立。——徐特立 12、真正的虚心，是自己毫无成见，思想完全解放，不受任何束缚，对一切采取实事求是的态度，具体分析情况对于任何方面反映的意见，都要加以考虑，不要听不进去。——邓拓 13、卑鄙和高傲的动机只会满足愚人、武夫、人类的侵略者和掠夺者的贪于，人们应当放弃这种动机，不要让这些诱人的饮料再麻醉那些自命不凡之徒！——圣西门 14、自卑虽是与骄傲反对，但实际却与骄傲最为接近。——斯宾诺莎 15、恢弘志士之气，不宜妄自菲薄。——诸葛亮 16、卑己而尊人是不好的，尊己而卑人也是不好的。——徐特立 17、当我们是大为谦卑的时候，便是我们最近于伟大的时候。——泰戈尔 18、盛满易为灾，谦冲恒受福。——张廷玉 19、昂着头出征，夹着尾巴回家，是庸驽而又好战的人的常态。——冯雪峰 20、每个人都有必定的理想，这种理想决议着他的尽力和断定的方向。就在这个意思上，我素来不把安适和快活看作生涯目标的自身——这种伦理基本，我叫它猪栏的幻想——爱因斯坦 21、好说己长便是短，自知己短便是长。——申居郧
反思自己的不足1000字
期末考试反思1000字2014年 紧张的期中考试已淡出我们的记忆，但我要提醒同学们不能忘了期中反思，因为通过反思，大家才可以发现平时学习上的不足与缺陷，考试就像捕鱼，每一次考试你都会发现鱼网上的漏洞，经过一次次的修补，一次次的捕捞，在高考的时候，你的知识与能力编成的鱼网一定已经是牢不可破的。这次期中考试，我们每一位同学都经受了失败、痛苦和成功的洗礼，得到了磨练、反省和升华自我的机会，这正是我们最大的收获。 但是，我们也要正确面对考试成绩。“不以物喜，不以己悲”，胜败乃兵家常事，对于一次考试的成功，我们不能盲目乐观，无论是谁，都不可能完美无缺，也许你还有许多弱点和缺点没有暴露，每份试卷都会有不同的结果。应该说，良好的开端是成功的一半，那另一半就是你要善于总结，不停地拼搏。假如你还一直陶醉在暂时的幸福中，失败只是迟早到来的结局。在顺利登上理想的彼岸之前，不轻言成功，这才是我们应取的态度。考试失利的同学也未必是坏事，失败是一支清醒剂，是不断成功的动力，即使我们一百次跌倒也要第一百零一次爬起，因为我们正处在人生攀登的山腰上，还有好长的路等待我们去开拓、创造。失败乃成功之母，有人说我怎么只遇到成功的母亲。是的，关键是你没有能抓住成功的父亲，那就是——“态度、目标、勤奋、恒心”。 态度决定一切。有这样一句话：“当我冷眼旁观时，生命是一只蓝色的蛹;当我热情相拥时，生命是一只金色的蝶”。学习也是这样，当你把学习当作自己成长发展的需要时，才能体验到学习的快乐;当你把学习当作是一种负担时，学习就是一种痛苦。谁愿在一片郁闷和痛苦中学习呢?所以说，我们首先要调整心态，以愉快的心情投入到紧张的学习生活中，并善于在学习的过程中体验获取知识的快乐，体验克服困难的快乐，体验取得成功的快乐。 目标是前进的灯塔。一个人没有目标，就象大海中迷失方向的航船，不可能达到成功的彼岸。生活中，每个人都应该有一个既定目标，瞄准目标奋力攀登，就一定会取得成功。最终的总体目标，是由一个个切近的具体目标逐步递进而实现的。因此，每个阶段性目标的实现都关系到总体目标的实现。在这个历程中，需要不断地将自己行为的结果与阶段性目标相比较。反思自己的目标，并进行合理的调节，制定出切合实际、通过努力能够达到的目标。 所以，请同学们一定要确立自己的努力方向和适当的近期目标，在不断的超越中成长自我，成就自我。 勤奋是成长的阶梯。书山有路勤为径，天上不会掉下馅饼，要学习真本领没有勤奋的耕耘不行。有句诗这样写到：“梦里走了许多路，醒来却还在床上”，不勤奋，理想永远是梦想。但勤奋并非只是简单的忙忙碌碌，更需要思考和反思。有的同学终日劳累，却没有明显的进步，原因何在?我想，也许是因为缺少思考和反思，还未认识到自己学习中的“短处”，课前不预习，抓不住关键的课堂学习环节，重作业轻复习，忽视学习规律的总结和学习方法的琢磨，学习在高耗和低效中进行。所以，我劝同学们忙中偷闲，时时反思自己的“短处”，力求一份耕耘两份收获!篇二：2015期中考试反思1000字 2015期中考试反思1000字 期中考试反思1000字范文一： 期中考试结束了，面对学生的学习成绩，虽然都比以前略有进步，但我觉得还是不够理想，所以在教学中有一些经验教训还是需要认真反思，以便能针对性的解决教学中存在的不足，使其成为以后教学工作有效的指导。 本次考试试题量大，考查的知识点非常全面，范围也极其的广泛，侧重于阅读能力和习作能力的考查，各占30%。学生在做的时候唯有细心、用心，并且知识面广，才有可能把题答好，取得高分。最让我意外的是解释字义这样的题又上演了，虽是重点词，上课也强调过，但从没复习，学生是很难得分的;更可气的是课本上没有，教参上却莫名其妙出现的无可厚非居然又一次被考;还有一些等到毕业前夕才要复习的一些诗句、名句也出现了。
菲利普斯曲线
菲利普斯曲线 菲利普斯曲线 菲利普斯曲线 表明失业与通货膨胀存在一种交替关系的曲线，通货膨胀率高时，失业率低;通货膨胀率低时，失业率高。菲利普斯曲线是用来表示失业与通货膨胀之间交替关系的曲线，由新西兰经济学家W?菲利普斯于1958年在《1861,1957年英国失业和货币工资变动率之间的关系》一文中最先提出。此后，经济学家对此进行了大量的理论解释，尤其是萨缪尔森和索洛将原来表示失业率与货币工资率之间交替关系的菲利普斯曲线发展成为用来表示失业率与通货膨胀率之间交替关系的曲线。 名称 菲利普斯曲线(Phillips Curve) 定义 1958年，菲利普斯根据英国1867,1957年间失业率和货币工资变动率的经验统计资料，提出了一条用以表示失业率和货币工资变动率之间交替关系的曲线。这条曲线表明:当失业率较低时，货币工资增长率较高;反之，当失业率较高时，货币工资增长率较低，甚至是负数。根据成本推动
的通货膨胀理论，货币工资可以表示通货膨胀率。因此，这条曲线就可以表示失业率与通货膨胀率之间的交替关系。即失业率高表明经济处于萧条阶段，这时工资与物价水平都较低，从而通货膨胀率也就低;反之失业率低，表明经济处于繁荣阶段，这时工资与物价水平都较高，从而通货膨胀率也就高。失业率和通货膨胀率之间存在着反方向变动的关系。 图中，横轴U值代表失业率，纵轴G值代表通货膨胀率，向右下方倾斜的PC 即为菲利普斯曲线。这条曲线表明，当失业率高(d)时通货膨胀率就低(b)，当失业率低(c)时通货膨胀率就高(a)。 最初是说明失业率和货币工资变动率之间交替关系的一条曲线。它是由英国经济学家菲利普斯根据1861—1957年英国的失业率和货币工资变动率的经验统计资料提出来的，故称之为菲利普斯曲线。因为西方经济学家认为，货币工资率的提高是引起通货膨胀的原因，即货币工资率的增加超过劳动生产率的增加，引起物价上涨，从而导致通货膨胀。所以，菲利普斯曲线又成为当代经济学家用以表示失业率和通货膨胀之间此消彼长、相互交替关系的曲线。 菲利普斯曲线三种表达方式 “失业,工资”菲利普斯曲线 第一种菲利普斯曲线表明的是失业率与货币工资变化率之间的关系。可称之
药物经济学复习笔记(第二章)
1、药物需要 是指医药专业人员根据现有医药知识所判定的一个人尽可能保持健康或变得健康而应获得或利用的某种药品的数量。医药专家判定的药品需要有一个共同的特征：即主要从人的健康需要出发。 2、药品需求 是指在某一特定时期、一定价格水平上，人们期望并能够购买的某种药品的数量。形成药品需求必须具备两个基本条件：医师消费者有购买药品的意愿；二是消费者有货币支付能力。 3、药品需要与药品需求的关系 （1）首先，药品需要是产生药品需求的基础。在药品需要的基础上，人们产生购买药品的意愿，进而形成实际药品需求。 （2）药品需要并不等于药品需求。要形成实际的药品需求，仅有药品需要是不够的，还必须具备两个基本条件：即消费者的支付能力和购买意愿。 （3）消费者对药品的实际利用（即需求）有时并不是建立在对药品客观需要的基础上。比如医生不合理诱导，患者对药物不合理或过度利用，就是一种没有需要的需求。 4、药品需求分析的目的 （1）概括的讲，认识药品需求的特征，了解人们对药品需求（或利用）的主要影响因素，掌握药品需求的变动趋势，进而为宏观和微观的决策服务。 （2）宏观讲，药物需求分析可以更加准确地预测未来整个社会药品资源利用状况以及变动趋势，为政府科学地确定产业发展计划和规划，合理配置和使用药品资源提供了依据。另外，政府也可以在了解药品需求主要影响因素的基础上，采取一定的政策措施对其中的某种或某些因素施加影响，以达到改变或控制药品需求或利用的目的。 （3）微观讲，药品需求分析有助于医药生产经营企业了解未来市场某种或某类药品的需求量以及需求的变动趋势，进而合理的生产和向社会提供适宜的药品，把握经营的主动权，取得良好的经济和社会效益。 5、药品需求的特征 （1）不确定性：消费者对药品的需求不像对食物、住房、衣物等得需求那样稳定和可以预知。 （2）最高优先性：一是指在人们诸多需求中，对药物的需求（特别是治疗药物的需求）应是优先予以满足的需求；二是一旦生病，人们普遍存在一种心理，希望找最好的医生，用最好的药物。 （3）不可替代性：人们的其他生活需求往往可以找到替代品，但药品几乎不可替代。 （4）外部效应性：药品需求不仅仅是个人的需求，也是一项社会需求。人们接受药物治疗，受益的不仅仅是个人，而且也会使其他社会成员受益。 （5）需求缺乏弹性：人们出现健康问题，药品是必需品，但在健康时，药品价格再便宜对人们也是无用的。药品价格提高，需求量未必减少，价格下降，需求量未必增加。 （6）被动性：病患者作为药品的直接消费者或需求者，一般不掌握药品知识，处于被动和被支配的地位，而掌握医药知识的医生为患者进行消费或购买选择，处于主动和决定的地位，容易诱导和创造需求。 （7）独特的需求三方结构：即病患者、医生（或药剂师）、医疗保险机构。决定了个人收入变化和药品价格变化对药品市场需求影响有限，而医疗保险政策以及医生的处方行为成为影响药品市场需求的重要因素。 6、药品需求的影响因素 （1）一般经济学因素 ①经济发展水平：社会经济发展水平影响居民个人和家庭的收入水平，而收入水平又会影响居民个人或家庭药品需求状况，药品需求与社会经济的发展水平呈直接的正相关，且药品消费的增长速度一般高于
学习是进步的阶梯
学习是进步的阶梯 ----听王文涛讲座心得 边院中学陈凤平 新的一学期就要开始了，为促进教师的专业成长，为学生的更好发展奠基，我们学校领导在开学初特地邀请了肥城市教科所王文涛老师作了题为《行走在教师专业成长的道路上》专题报告。 7月26日下午，我们边院中学的老师，早早的来到二楼会议室静候王老师的到来，聆听王老师的报告。 本次专题讲座的内容主要三个方面进行，一是翻转课堂的实施；二是课题研究的进行；三是教育反思的撰写。 王文涛老师从翻转课堂的起源、概念、教学结构特点、翻转课堂的基本类型、实施程序以及手段等方面做了经典的讲解；在课题研究方面，王老师从教师为什么做课题研究、如何设计研究、如何开展研究、如何呈现研究成果、研究成果的使用等五个层面进行了诠释和解析；在撰写教育反思方面，王老师重点从教师如何撰写教育反思和教研论文方面进行了详实的指导。 长达3个小时的专业发展报告给我很大的启发：世界每天都是新的，我们的工作每天也是新的，不学习新的知识就会落伍跟不上时代的步伐。不反思不总结就会止步不前，在这个日新月异的时代，止步就是退步。通过学习，我对于微课程、翻转课堂、课题研究等这些深感困惑的理论有了比较清晰的认识。
听完王老师的报告，回想了自己20多年的教学生涯，刚开始工作那几年的的上进心，求知欲所剩无几，记得刚毕业时为了尽快的熟悉自己的所教的课程，自发、自费的订阅《中学物理》、《中学物理教学参考》等书籍。用心的听老教师的课，虚心的学习，到外地听课仔细地记录，认真的学习，把学来的东西用到自己的课堂上。我的课堂曾一度也取得了比较满意的效果，也曾得到了教研室等领导的认可，学生的好评。可是这几年，我觉得自己的课堂，自己的发展遇到了瓶颈期，以前的模式总在笼罩着我，难以突破。总觉得只要按以前的模式上好课，就万事大吉了。 今天突然意识到：现在的好课堂已今非昔比，今天的高效课堂要有现代理论的支撑，要有各种现代技术的融入，要有现代的理念的引领。所以，我想自己应该像小学生那样对新生事物充满好奇心，不断学习新的知识，尝试新的事物，不嫌麻烦，以积极的，年轻的心态迎接每一天。
9章菲利普斯曲线
第九章 菲利普斯曲线 本章解释失业的分类、影响，通货膨胀的定义、成因以及效应，研究失业与通货膨胀之间的关系，并利用菲利普斯曲线分析总需求管理的效果。 第一节 通货膨胀 一 通货膨胀的定义与衡量 1如何理解通货膨胀 通货膨胀是指物价水平的持续上升过程或者货币价值的持续下降过程。理解通胀可以有以下层次：首先，通货膨胀是一个过程，而不是短期价格波动。其次，通货膨胀是指整体物价水平的上涨。而不是少数产品的价格上涨。其三，可以从价格或货币角度观察通货膨胀。 2通货膨胀是可以度量的。 1%100－基期物价水平 预测期物价水平?=π在中国，用1－CPI =π表示。 二 通货膨胀的成因（利用AD-AS 图形分析） 1需求拉上型的通货膨胀 通俗地说就是钱太多，货太少。政府扩张性的财政与货币政策导致流动性过大。通常是通货膨胀的最主要原因。如图： 2成本推进型通货膨胀 由于垄断以及经济活动中投入要素价格的上涨所导致的通货膨胀，叫成本推进型通货膨胀，如图： 3结构型通货膨胀：一个国家或者是地区由于生产率差异而
导致的通货膨胀。 4输入型通货膨胀 在开发经济条件下，一国通货膨胀率等于货币贬值率加外国通货膨胀率。可以根据购买力平价理论和一价定律推导出这一结论。在市场统一、产品同质等假设下，由于有P e P * =,即产品在国内的价格，等于汇率乘以外国价格。那么就有： ' +'='*P e P 假设经济完全开放，一国在2009年货币贬值率为5%，外国通货膨胀率为10%。2009年名义GDP 为40万亿元，可以计算该年的实际GDP 。联系2009-2012中国的通货膨胀事实，说明导致该时期通货膨胀压力的主要因素。 三 通货膨胀的效应 1通货膨胀对收入和财富分配的影响： （1）通货膨胀将会产生通货膨胀税，所以通货膨胀对政府有利，对私人不利。
中国医学史名词解释
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虚心向别人学习的名言
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造，然后再回顾一下我的知识，我觉得自己简直是浅陋之极。;;伽利略 10.我们各种习气中再没有一种象克服骄傲那么难的了。虽极力藏匿它，克服它，消灭它，但无论如何，它在不知不觉之间，仍旧显露。;;富兰克林 11.有了一些小成绩就不求上进，这完全不符合我的性格。攀登上一个阶梯，这固然很好，只要还有力气，那就意味着必须再继续前进一步。;;安徒生 12.真正以谦虚是最高的美德，也即一切美德之母。;;丁尼生 13.啊!夸奖的话，出于自己口中，那是多麽乏味!;;孟德斯鸠 14.一个骄傲的人，结果总是在骄傲里毁灭了自己。;;莎士比亚 15.一切真正的和伟大的东西，都是纯朴而谦逊的。;;别林斯基 虚心向别人学习的名言锦集1.谦虚是最高的克己功夫。;;莎士比亚 2.当你意识到自己是个谦虚的人的时候，你马上就已经不是个谦虚的人了。;;列夫;托尔斯泰 3.妄自尊大只不过是无知的假面具而已。;;伏尔泰 4.九牛一毫莫自夸，骄傲自满必翻车。历览古今多少事，成由谦逊败由奢。;; 陈毅 5.不满足是向上的车轮。;; 鲁迅 6.劳谦虚己，则附之者众;骄慢倨傲，则去之者多。;; 葛洪 7.恃国家之大，矜民人之众，欲见威于敌者，谓之骄兵。;; 魏
反思,教师进步的阶梯
反思，教师进步的阶梯 发表时间：2013-07-25T16:59:52.233Z 来源：《中小学教育》2013年11月总第151期供稿作者：李伟娜 [导读] 反思一旦成为了教师的一种生活方式，那么教师所获得的绝不仅仅是专业成长，而是整体生命高速度、高质量的成长。 李伟娜山东省栖霞市实验中学265300 反思是人对自己的行为以及由此产生的后果进行审视和分析的过程，是一种理解与实践之间的对话，包括引起思维怀疑，寻找、搜索和探索的活动，求得解决疑难、处理困难的办法。通过反思，才能更好地理解事物的本质和规律，有效地把握事物内在联系，形成新的判断，获得新的知识；才能促进人自身的发展，为创新的开展打下良好的基础。波斯纳认为：教师的成长=经验+反思。由此可见，作为教师，面对当前的教育形势，要想取得理想成绩，除了一定的教学经验外，离不开经常性的反思。 从教学实践来看，我认为教学反思要注意做到以下几个方面： 一、课前反思——提高教学针对性 这是一种前瞻性反思：教师在上课前认真思考本节课备课是否充分，备课时是否遇到了什么困难，是否调整了教材，为什么这样调整，教具、资料是否准备齐全，本节课必须实现的教育教学目标是什么。这样做，可以提高教学的针对性，使自己的教学行为成为一种自觉的教学实践。 二、课中反思——确保教学有效性 在授课的过程中，随着师生的互动，学生的提问或者是有独到见解的回答，必然与教师的备课或多或少地发生一些碰撞，对教师产生一些新的启迪。这就需要教师不断地反思：哪些观点更合理、更全面？学生还有哪些不懂的地方？重难点的确立是否得当？自己还应补充哪些方面的知识、加强哪方面研究？教案还应做哪些修改？……通过反思，教师就可以从总体上把握全班学生的实际性重难点，即时调整教学，更好地因材施教，提高教学效益。 三、课后反思——完善教学、促进高效 教学后撰写教学后记，系统地回顾本节课的教学全程，思考每一个教学环节的得与失，不仅有助于完善本节课的教学，更重要的是能促进教师教学反思的常态化，养成善于总结、及时反思的习惯，促进教师的专业成长和不断成熟。写教学后记是课后反思的主要形式，也是教师撰写教育教学论文的第一手资料来源。教学后记的撰写主要包括以下五个方面： 1.记成功之举。 要将教学过程中达到预先设计的目的、引起教学共振效应的做法，课堂临时应变得当的措施，层次清楚、条理分明的板书，某些教学思想方法渗透与应用的过程，教育学、心理学中一些基本原理使用的感触，教学方法上的改革与创新等等详细记录下来，供以后教学时参考使用，在此基础上不断地改进、完善、推陈出新。 2.记“败笔”之处。 3.记教学机智。 “智慧的火花”常常是不由自主、突然而至，若不及时利用课后反思去捕捉，便会因时过境迁而烟消云散，令人遗憾。 4.记学生的创新见解。 学生在课堂上提出的一些独到的见解难能可贵，也是对课堂教学的补充与完善，可以拓宽教师的教学思路，提高教学水平。 5.记再教设计。 一节课下来，静心沉思体会出了哪些教学规律、教法上有哪些创新、知识点上有什么发现、组织教学方面有何新招、解题的诸多误区有无突破、启迪是否得当、训练是否到位等等，及时记下这些得失，并进行必要的归类与取舍，考虑一下再教这部分内容时应该如何做，写出“再教设计”，这样可以扬长避短、精益求精，把自己的教学水平提高到一个新的境界。 四、练习和考试后反思——教学后反思不可缺少的环节 根据人的记忆规律，在学习初期，知识遗忘得较快，需要及时地巩固和提高，因此布置相应的练习和进行阶段性的考试就显得非常必要。练习正确率的高低和考试成绩的好坏在一定程度上反映了学生对所学知识的掌握情况和应试能力的高低。 通过练习与考试，教师应从以下几方面进行反思： 一是练习。 通过对练习题的批改，一方面教师应反思练习题是否全面覆盖了学生应学的知识、是否适合学生实际水平、是否达到了通过练习使学生掌握知识的目的；更为重要的是教师应通过对练习中存在问题的分析，反思学生的思维过程和问题所在，进行有针对性的指导讲解，从而提高学生的逻辑思维能力和对知识的理解、应用能力。 二是考试。 通过对试卷的批改和对错题的分析，教师首先应反思自己的教学有没有没讲到的或者是没给学生讲明白的地方。 其次要反思对学生进行审题思路、解题方法和技能的指导是否到位。 第三要反思试题的难易程度、每一道题目的立意是否达到了预期目的。 通过这些思考，就可以在试卷讲评时进行有针对性的讲解和强化训练，达到更为有效地帮助学生学习和全面提高学生各方面能力的目的。 教学反思，贵在坚持，贵在执着。一有所得，及时记下，以记促思，以思促教，教师的教学水平和能力必定会有长足的进步。反思一旦成为了教师的一种生活方式，那么教师所获得的绝不仅仅是专业成长，而是整体生命高速度、高质量的成长。
药物经济学名词解释
药物经济学名词解释 药物经济学：泛指西方经济学在药物治疗评价上的应用，包括一切有关药物在临床应用俄经济学研究。 药物经济学的研究方法：成本效益分析（CBA）成本效果分析（CEA）,最小成本分析（CMA）成本效用分析（CUA） 全社会观点考虑所有的社会成本和效益，着重全社会的总社会变化、而不关心成本、效益的承受者以及可能的财产再分配 药品的需要：所谓的药品的需要，是指专业人员根据现有医药知识所判定的一个人尽可能保持健康或变得健康而应获得或利用的某种药品的数量 药品需求：所谓的需求是指在某一特定时期、一定时期、一定价格水平上，能购买的某种药品的数量。 没有需要的需求：消费者在医生的不合理诱导下对药品的不合理或过度需求（或利用），就是一种没有需要的需求 药品价格：即药品本身的价格。 药品的相对价格：是指在扣除了医疗（或保障）付款后，由消费者个人支付的那部分药品价格。 需求法则：需求量与价格之间的这种反向的变动的关系 需求弹性可分为需求价格弹性、收入弹性、交叉弹性等，它们分别说明需求量变动与价格、收入、相关产品价格变动之间的关系。 需求价格弹性：需求价格弹性，是指价格变化引起的需求量的相应变动率 供给弹性：是指供给量变化的百分比对于价格变化百分比的比率 药品供给：是与药品需求相对应的一个概念。是指药品生产者或提供者在一定时期内的一定价格水平上，愿意并能够提供的某种药品的数量。形成药品供给也需要两个基本的条件，一，由供给意愿，二由供给能能力 价值规律和供求规律是市场上商品或服务价格决定的两个最重要的规律 药品经济学的研究按照其应用的对象不同可分为调查研究、临床研究和实验研究 随机化分组：是指每个研究对象被分到各组的概率是相等的，而不是有意的或无意的按某种倾向把研究对象分配到对照组或实验组 普查：亦称全面调查，就是将组成的总体的所有观察单位全部加以调查 抽样调查：是一种非全面调查，它是从总体中抽取一定数量的地观察单位组成样本，然后用样本推断总体 医学研究的基本要素包括处理因素、受试对象和实验效应 统计方法主要考虑对照、重复、随机化——实验设计原则 总体：是同质的个体所构成的全体 样本：我们往往不可能研究组成总体的所有个体，而只能从总体中区部分个体的过程称为抽样，所抽的的部分称为样本 概率：是反映某一事件发生的可能性，用P表示。概率P<0.05和（或）P<0.01来作为事物差异有统计学意义与有高度统计学意义的判断标准 效度：是指测量指标或观测结果在很大的程度上反映了事物的客观真实性 信度：是指在相同条件下，对同一事物重复测量若干次，测量结果的降服程度，说明数据的可考性 成本；是指在某乡生产，服务等过程中所消耗的物化劳动的货币值 医疗成本:是医院为社会提供医疗服务过程中所发生的物化劳动和活劳动的总合。 质量调整生命年：因疾病或伤残造成的生活痛苦，相比较完全的健康的生活，会让人感觉火
虚心是进步的阶梯作文500字
虚心是进步的阶梯作文500字 各位读友大家好！你有你的木棉，我有我的文章，为了你的木棉，应读我的文章！若为比翼双飞鸟，定是人间有情人！若读此篇优秀文，必成天上比翼鸟！ 习思英语竞赛才刚刚过去不久，它在我的心中留下了不可磨灭的印象。那天是12月17日，妈妈带我去龙港一中参加英语竞赛。我们到达龙港一中时。离考试还有四五十分钟，校门还没有开，我们就在旁边等着。大约到了半个小时，其他的同学也陆陆续续到了，校门才开。我告别妈妈，随着人流走进了学校。我走到自己的考场后，就安静地坐在自己位置上。大部分同学一坐下来就开始看单词表，我可从来不这样。经过几次考试我已经得出了经验：在考试中单词表上的单词几乎不会出现，功夫在平时的积累。所以最好趁这个时间好好放松，做好准备。到了九点整，比赛正式开始了。我开始认真做笔试部分，不敢马虎。
过了十几分钟，听力开始放，教室里静得没有一点声响，每个人都生怕自己听漏了什么细节。我就一直疯狂地做题，怕后面的时间不够。阅读题、作文……当我写好最后一个单词时，我的心猛地一阵激动，差一点就跳起来了。我看看表，还有8分钟呢！我突然想起了妈妈考前对我说，虚心是进步的阶梯，写好后认真检查，就不会给自己留下遗憾。于是，我平静下来，仔细地检查试卷，果然检查出了几处小错误，一个一分呢！不检查就得白白扣掉多少冤枉分啊！我才明白了虚心的重要。8分钟一晃儿就过去了，铃声响了起来，我信心满满地交了试卷。凡事都抱着虚心的态度，会给你带来喜悦和成功。 各位读友大家好！你有你的木棉，我有我的文章，为了你的木棉，应读我的文章！若为比翼双飞鸟，定是人间有情人！若读此篇优秀文，必成天上比翼鸟！
接受就是最好的面对,反思就是最真的成长
接受就是最好的面对，反思就是最真的成长 人生，是一场没有约定的旅行，事先你根本不知道自己要到哪里去，也不知道会遇到什么样的人和什么样的事，你总是在不知不觉的经历着、体会着、忙碌着、接受着、反思着，同时也享受着、快乐着、幸福着。 人生，既有快乐也有烦恼，既有成功也有失败。你坚强了，一切都能化险为夷，逢凶化吉；你脆弱了，事事会恶性循环，寸步难行；你接受了，一切都会风平浪静，海阔天空；你反思了，失误了可以得到修正，失败了可以重振旗鼓。 一路上，你会领略到不同的风景，也会遇到不同的人。不同的风景会给你不同的感受，不同的人会给你不同的人生。 假如你遇到爱你的人，他们总能给你理解、包容和生活的热情，一路与你风雨相伴，荣辱与共。他们关心你，爱护你，给你自由飞翔的天空。成功了，给你祝贺；失败了，给你勇气；快乐了，与你分享；痛苦了，与你分担。 假如你遇到你生命里的贵人，他们总能给你机遇和帮助，扶上马再送一程。他们无私地鼓励你、鞭策你，使你扬长避短，更加优秀。他们给你提供成功的机会和保障，给你带来无穷的动力和希望。他们是你进步的阶梯，使你从一个辉煌走向另一个辉煌；他们也是你生存的阳光，使你健康快乐成长。无论何时，你都要心存感恩，把贵人永远记在心上。 假如你遇到伤害你的人，他们的伤害会使你警钟长鸣、催你反思；也让你深深懂得不能把善良施予每一个人，因为有些人是不值得你付出的，他们会把你的善良当作傻瓜、当作软弱，不但不懂得感恩，反而恩将仇报、过河拆桥，甚至做出不仁不义之事，令人痛心，让人心寒。 经历了伤害，你能看清什么是丑恶；经历了伤害，你才会深刻反思；经历了伤害，你才会吃一堑，长一智；经历了伤害，你才明白上天很公平，让你遇到一个恶人的同时又让你遇到更多的好人。 一路上，你会遇到风平浪静，也会遇到暗流汹涌；会遇到鲜花遍地，也会遇到荆棘丛生；会遇到阳光灿烂，也会遇到凄风冷雨。无论你遇到什么，接受就是最好的面对，反思就是最真的成长。 人生，是一场旅行，你与不同的人携手前行，有的人走着走着就散了；有的情走着走着就淡了；有的爱走着走着就冷了；有的心走着走着就远了。 人生，是一场旅行，走着走着你就长大了，走着走着你就明白了，走着走着你就成熟了，走着走着你就智慧了。这一切的一切都在不经意间发生，哪怕碰得头破血流也无怨无悔，因为所有的这些都在意料之外，又在情理之中。
吉大2020年9月课程考试《药物治疗学》离线作业考核试题及答案
1.何谓特殊人群对妊娠妇女和儿童用抗菌药应特别注意什么? 答案：特殊人群主要包括老年人、儿童、妊娠期和哺乳期妇女及肝、肾功能不全者等患者。这部分人群由于其自身的生理、病理变化往往会影响药物的吸收、分布、代谢和排泄，同时也影响药物的效应和不良反应。妊娠哺乳期用药：原则上应权衡利弊后，使用抗生素的利大于其毒副作用时方可使用。较安全的有青霉素类、头抱菌素类和β-内酰胺类、大环内酯类、克林霉素类等。应避免使用氨基糖苷类、四环素类、大环内酯类、喹诺酮类、磺胺类等。儿童用药：可使用青霉素类、头孢菌素类、大环内酯类，慎用克林霉素类、氨基糖苷类等，应避免使用四环素类、喹诺酮类等。 2.试说明下表中A型药物不良反应和B型药物不良反应的特点和发生的原因。 答案：1、A型药物不良反应发生的原因：1)动力学方面的原因①药物的吸收②药物的分布A、药物在循环中分布的量和范围取决于局部血液量和药物穿透细胞膜的难易B、药物与血浆蛋白的结合C、药物与组织结合③药物的排泄④药物的代谢2)药效动力学方面的原因2、B型药物不良反应发生的原因：1)药物的因素：包括有效成分的分解产物、添加剂、增溶剂、稳定剂、着色剂、赋型剂、化学合成中产生的杂质等。2)患者的因素：①特异质因素，由于患者本身原因而引起的B型不良反应，主要与患者的特异性遗传
素质有关。②免疫学因素。 3.循证医学(名词解释) 答案：循证医学(Evidence-basedmedicine，缩写为EBM)，意为“遵循证据的医学”，又称实证医学，港台地区也译为证据医学。其核心思想是医疗决策(即病人的处理，治疗指南和医疗政策的制定等)应在现有的最好的临床研究依据基础上作出，同时也重视结合个人的临床经验。 4.治疗窗(名词解释) 答案：治疗窗(therapeuticwindow)，指治疗浓度的范围，即介于最小有效浓度和最小中毒浓度之间的血药浓度。 5.医疗用毒性药品(名词解释) 答案：医疗用毒性药品，系指毒性剧烈、治疗剂量与中毒剂量相近，使用不当会致人中毒或死亡的药品。 6.安全范围(名词解释) 答案：安全范围是指药物的最大有效量与最小中毒量之间的范围。 7.药物经济学(名词解释) 答案：药物经济学是经济学原理与方法在药品领域内的具体运用。 8.药物治疗不依从性(名词解释)
工作,状态,总结,反思
工作,状态,总结,反思 自我工作反思 工程部—××× 根据公司近期出现的个别员工执行力差、工作效率低以及部门之间配合意识差等问题，现对自己工作进行反思，具体情况如下： 1、执行力：在日常工作中严格按照工程管理规范要求进行检查施工，但有时也对施工队要求不严，出现问题；犹如安全防护、现场卫生等问题；工作不够深入，工作上不够扎实，规范上不够细致。由于日常的工作情况已大致掌握，工作一直侧重于传达，安排，落实，主观上认为这就是工作重点，如果对实施过程做的更细致，有些事情会达到更好的效果，也导致有些深层次的问题不能全面掌握。 2、工作效率：在日常工作有时会出现与施工单位沟通不够，心态有时较为浮躁，不能平心静气解决问题；主要原因是履行职责不到位，缺乏责任感，对待工作不够努力，不够细，工作完成后未能做进一步检查，工作质量得不到保证，甚至做无用功，工作效率低。 3、部门配合上：工程部作为公司后勤部门，主要为各车间及部门服务，但我在服务上做的不够好，全局意识不够强，做事只从本身工作出发，在工作中有时带有个人情绪，没有全身心投入工作，在服务上不够精细，处理问题太表面。 出现以上问题主要是自己缺乏责任感，对待工作不努
力；责任意识，大局意识不够强，忽视了工作的积极性、主动性、创造性，有一种知足于现有水平的思惟。 在今后的工作中我一定 要进一步改进工作作风，要努力做到善于克服消极思维，破除暴躁情绪；加强自身建设，努力学习本职工作需要的专业知识和业务技能，精益求精工作手段和工作方式，自我加压始终保持积极向上的精神状态，高标准严要求，做好本职工作。 工作反思 开学已经两个月了，在这两个月里，我班的教育教学取得了一定的成果但也存在许多不足，现将这两个月的工作进行如下小结。 一、行为习惯方面： 在开学初小朋友们的各种常规行为散漫无序，因此在这两个月中我主要是抓学生的常规习惯的教育，通过了这二个月的学习和教育，各方面的常规都了进步，表现在课堂上能够提前准备上课的学具，知道了回答问题要举手，如果大声喊叫老师不仅不让回答问题甚至还要批评，知道了早晨来了要把作业交给组长，下课了要及时收拾桌面。作为科任教师，不仅规范学生的课堂行为，对于其他方面，也积极配合班主任做好常规养成教育，特别是排队上间操，小朋友们都好了许多，卫生习惯也有了不小的进步。午休秩序也有了明
第七章 菲利普斯曲线(教学)
第七章菲利普斯曲线 一、定义 表明失业与通货膨胀存在一种交替关系的曲线，通货膨胀率高时，失业率低；通货膨胀率低时，失业率高。菲利普斯曲线是用来表示失业与通货膨胀之间交替关系的曲线，由英国经济学家W·菲利普斯于1958年在《1861－1957年英国失业和货币工资变动率之间的关系》一文中最先提出。此后，经济学家对此进行了大量的理论解释，尤其是萨缪尔森和索洛将原来表示失业率与货币工资率之间交替关系的菲利普斯曲线发展成为用来表示失业率与通货膨胀率之间交替关系的曲线。 1958年，菲利普斯根据英国1867－1957年间失业率和货币工资变动率的经验统计资料，提出了一条用以表示失业率和货币工资变动率之间交替关系的曲线。这条曲线表明：当失业率较低时，货币工资增长率较高；反之，当失业率较高时，货币工资增长率较低，甚至是负数。根据成本推动的通货膨胀理论，货币工资可以表示通货膨胀率。因此，这条曲线就可以表示失业率与通货膨胀率之间的交替关系。即失业率高表明经济处于萧条阶段，这时工资与物价水都较低，从而通货膨胀率也就低；反之失业率低，表明经济处于繁荣阶段，这时工资与物价水平都较高，从而通货膨胀率也就高。失业率和通货膨胀率之间存在着反方向变动的关系。 图中，横轴U代表失业率，纵轴G代表通货膨胀率，向右下
方倾斜的PC即为菲利普斯曲线。这条曲线表明，当失业率高（d）时通货膨胀率就低（b），当失业率低（c）时通货膨胀率就高（a）。 最初是说明失业率和货币工资变动率之间交替关系的一条曲线。它是由英国经济学家菲利普斯根据1861—1957年英国的失业率和货币工资变动率的经验统计资料提出来的，故称之为菲利普斯曲线。因为西方经济学家认为，货币工资率的提高是引起通货膨胀的原因，即货币工资率的增加超过劳动生产率的增加，引起物价上涨，从而导致通货膨胀。所以，菲利普斯曲线又成为当代经济学家用以表示失业率和通货膨胀之间此消彼长、相互交替关系的曲线。