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测量了LaCoO3单相多晶样品的纵波与横波超声声速和衰减随温度的变化关系, 在材料的自旋态转变温度附近(≈90K),纵波声速出现明显的软化并伴随一个尖锐的衰减峰,但是在横波的测量中却没有出现类似的超声异常,分析认为LaCoO3在90K附近的自旋态转变是由于Co3+离子是从低自旋态(LS,t62ge0g)转变到中等自旋态(IS,t52ge1g ),而不是高等自旋态(HS,t42ge2g).随着温度的升高,在200K附近纵波和横波测量上都观察到一个伴随着微小声速软化的宽大的衰减峰,这可能是随机分布的IS态Co3+离子的Jahn-Teller效应导致的局域晶格扭曲所造成的. 相似文献
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通过理论计算研究GaMnN铁磁共振隧穿二极管自旋电流输运特性.理论结果表明在电流特性曲线上出现两个明显的自旋分裂峰.该电流自旋分裂峰和相应的自旋极化随温度的升高而逐渐减小消失.当进一步考虑到GaN异质结界面极化电荷影响时,自旋向下的电流共振峰得到明显增强,同时电流的自旋极化也得到相应的提高.在一定的极化电荷条件下,可以获得较高的自旋极化电流.
关键词:
GaMnN
共振隧穿
自旋电流
极化电荷 相似文献
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在球形相对论平均场模型下, 采用NLSH相互作用全面研究了从Sn质子滴线核到Sn中子滴线核的自旋对称性和赝自旋对称性. 发现: 1) 随着核子数的增大, 中子和质子的赝自旋波函数劈裂基本上都是减小的, 并且质子的变化趋势更加明显. 中子高能级的自旋波函数劈裂随着核子数的增大也是减小的. 2) 对于特定的同位素, 当n=1时, 赝自旋波函数劈裂随着l的增大而增大. 当n=2时, 中子的自旋波函数劈裂随着l的增大而增大. 当l=2或l=3时, 中子的自旋波函数劈裂随着n的增大而增大. 3) 中子和质子的赝自旋劈裂之间的差别总是比自旋劈裂的差别更大一些. 相似文献
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测量了LaCoO3单相多晶样品的纵波与横波超声声速和衰减随温度的变化关系, 在材料的自 旋态转变温度附近(≈90K),纵波声速出现明显的软化并伴随一个尖锐的衰减峰,但是在 横波的测量中却没有出现类似的超声异常,分析认为LaCoO3在90K附近的自旋态 转变是由于Co3+离子是从低自旋态(LS,t62ge0 g)转变到中等自旋态(IS,t5 2ge1g ),而不是高等自旋态(HS,t42ge2g).随着温度的升高,在 200K附近纵波和横波测量上都观察到一个伴随着微小声速软化的宽大的衰减峰,这可能是随 机分布的IS态Co3+离子的Jahn-Teller效应导致的局域晶格扭曲所造成的.
关键词:
超声声速与衰减
自旋态转变
Jahn-Teller效应 相似文献
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通过求解具有Woods-Saxon径向标量势与矢量势的Dirac方程, 分别分析了原子核中赝自旋双重态能级劈裂和波函数下分量劈裂随着Woods-Saxon势参数的变化关系, 其中Wood-Saxon势中的参数a以及R对于赝自旋能级劈裂和波函数劈裂的影响最大, 而势阱深度V0只产生微小的影响. 随着平均场的变化, 赝自旋双重态会出现能级反转现象. 具有较大n或l的赝自旋双重态能级劈裂对于参数的变化更敏感. 赝自旋波函数下分量劈裂随着参数a和R的增大向核表面扩散, 并且在核表面附近达到最大. 赝自旋波函数劈裂随着参数a的增大而增大, 但是随着参数R或V0的增大它却在减小的. 由于在特定的同位素链中, 参数R和V0都与核子数有关系, 而参数a又是描述核的表面性质的, 所以以这些参数为变量对于赝自旋劈裂的研究是有意义的, 研究的结果至少在定性上可以应用到大部分原子核中. 相似文献
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作为寻找新型自旋电子学功能材料的尝试,文章详细研究了稀土化合物GdN的电子结构和磁学性质,通过第一性原理的理论计算,作者发现该材料的导电性质随体积增加有很大变化:从半金属态到准金属态,最后成为半导体.同时,施加压力能改变其载流子浓度和位于多数自旋态的电子和空穴的迁移率.对其磁交换参数随品格常数变化的进一步研究和蒙特卡罗模拟表明,这个铁磁体系的居里温度可以通过加压或掺杂得到进一步提高,从而成为很有实用价值的自旋电子材料. 相似文献
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The crystal structure, magnetic and electronic properties of SmFeO3 under hydrostatic pressure have been studied by first-principles calculations within the generalized gradient approximation plus Hubbard U (GGA + U). The iso-structural phase transition with spin, volume and band gap collapses can be induced by a large enough hydrostatic pressure. The high-spin (HS) state of Fe3+, with the magnetic moment of ~4 μB, is retained at low pressure. The spin crossover occurs at a transition pressure (~68 GPa) with the magnetic moment of Fe3+ decreasing to ~1 μB in low-spin (LS) state. Meanwhile, the reductions of cell volume (by ~?5.43%) and band gap (from >2 eV to ~1.6 eV) of SmFeO3 are obtained when the HS–LS transition happens. Finally, the critical pressure of HS–LS transition, magnetic and electronic properties are found to be Hubbard U dependent. 相似文献
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The possibilities to trap by flash cooling the high spin (HS) state of iron(II) in the [Fe(PM-BiA)2(NCS)2] complex have been investigated by X-ray diffraction. This study reveals that trapping the HS state is possible under some conditions depending on the final temperature. If the latter is lower than the T(LIESST) temperature, the HS→LS (low spin) relaxation is slow enough to determine the trapped HS crystal structure by X-ray diffraction. The crystal structure of this complex in the 30 K trapped HS state shows differences from either the room temperature (HS) or the 30 K (LS) crystal structures, as for example differences in the strength of the S?H-C hydrogen bond like intermolecular interaction or the π-π interactions, known to play a crucial role in this compound for the propagation of the change in spin at the spin crossover (SCO), i.e. the cooperativity. The differences in intermolecular interactions are directly linked to the differences between the crystallographic unit cell modifications induced by pure thermal effects and those induced by the SCO. 相似文献
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A new type III of 3,5-lutidine spin crossover coordination compound with formula Fe(3,5-lutidine)2Ni(CN)4·2[(H2O)(3,5-lutidine)] 2c has been obtained. The ratio of the high spin state (HS) iron (II) changing to the low spin state (LS) iron (II) in 2c is higher than that of type I and type II 3,5-lutidine coordination polymer 2a and 2b previously reported. 57Fe Mössbauer spectra of 2c show two different doublets which correspond to HS1 (inner doublet lines) and HS2 (outer doublet lines). The intensity of the HS1 doublet decreases on cooling to 80 K while the intensity of another component, the LS singlet, increases. The 90 % of the HS1 doublet change to the LS singlet is probably due to suitable environments of octahedral iron (II) ions coordinated by four nitrogen atoms of cyano groups and two nitrogen atoms of 3,5-lutidine ligands. We also prepared the Hofmann-like 3,5-dichloropyridine coordination compound Fe(3,5-dichloropyridine)2Ni(CN)4 ·2[(3,5-dichloropyridine)(H2O)] 2d to compare it with 2c. 57Fe Mössbauer spectra of 2d show that 2d is not a spin crossover coordination compound. 相似文献
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M. L. Savchenko Z. D. Kvon S. Candussio N. N. Mikhailov S. A. Dvoretskii S. D. Ganichev 《JETP Letters》2018,107(4):247-253
The magnetic properties of the α-Fe2O3 hematite at a high hydrostatic pressure have been studied by synchrotron Mössbauer spectroscopy (nuclear forward scattering (NFS)) on iron nuclei. Time-domain NFS spectra of hematite have been measured in a diamond anvil cell in the pressure range of 0–72 GPa and the temperature range of 36–300 K in order to study the magnetic properties at a phase transition near a critical pressure of ~50 GPa. In addition, Raman spectra at room temperature have been studied in the pressure range of 0–77 GPa. Neon has been used as a pressure-transmitting medium. The appearance of an intermediate electronic state has been revealed at a pressure of ~48 GPa. This state is probably related to the spin crossover in Fe3+ ions at their transition from the high-spin state (HS, S = 5/2) to a low-spin one (LS, S = 1/2). It has been found that the transient pressure range of the HS–LS crossover is extended from 48 to 55 GPa and is almost independent of the temperature. This surprising result differs fundamentally from other cases of the spin crossover in Fe3+ ions observed in other crystals based on iron oxides. The transition region of spin crossover appears because of thermal fluctuations between HS and LS states in the critical pressure range and is significantly narrowed at cooling because of the suppression of thermal excitations. The magnetic P–T phase diagram of α-Fe2O3 at high pressures and low temperatures in the spin crossover region has been constructed according to the results of measurements. 相似文献
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The thermal- and photon-induced phase transitions of [Fe(2-pic) 3 ]Cl 2 EtOH from a high-spin (HS) state ( S = 2) to a low-spin (LS) state ( S = 0) were observed by X-ray Emission Spectroscopy (XES) and X-ray Absorption Spectroscopy (XAS). The spin state was observed with Fe 3p-1s XES from the HS and photon-induced (PI) phase took S = 2 and LS state took S = 0. Each spectrum of the decay process from the PI phase to the LS state could be described with the superposition of those of the HS and LS states. In XAS, a different spectrum was also observed in the HS and LS states, and likewise by XES; the difference in the pre-edge structure between the HS and LS states was explained based on the difference of Fe unoccupied 3d partial density of state calculated by the DV-X f method. 相似文献
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采用平面波赝势方法对菱铁矿FeCO3高压下的晶体结构, 电子构型和电子结构进行了第一性原理计算研究. 研究过程中考虑了菱铁矿FeCO3真实的反铁磁(AFM) 自旋有序态, 模拟静水压环境, 从零压逐步加压到500 GPa. 在40---50 GPa压力范围内, FeCO3发生了从高自旋(HS) AFM态到低自旋(LS) 非磁性(NM) 态的磁性相变, 伴随着晶胞体积坍塌10.5%. FeCO3在相变前后均是绝缘体, 但是相变后的LS-NM态的Fe2+ 离子的3d电子局域化程度更强, 能隙随着压力的进一步增大而逐步增大, 离化程度更高, 直到500 GPa没有发生金属绝缘体相变. 相似文献
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Iron in the major lower mantle (LM) minerals undergoes a high spin (HS) to low spin (LS) transition at relevant pressures (23-135 GPa). Previous failures of standard first principles approaches to describe this phenomenon have hindered its investigation and the clarification of important consequences. Using a rotationally invariant formulation of LDA + U we report a successful study of this transition in low solute concentration magnesiowüstite, (Mg(1-x)Fe(x)(O), (x < 0.2) the second most abundant LM phase. We show that the HS-LS transition goes through an insulating (semiconducting) intermediate mixed spins (MS) state without discontinuous changes in properties, as seen experimentally. We show that the HS state crosses over smoothly to the LS state passing through an insulating MS state where properties change continuously, as seen experimentally. 相似文献
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Takafumi Kitazawa Madoka Sekiya Takeshi Kawasaki Masashi Takahashi 《Hyperfine Interactions》2016,237(1):29
57Fe Mössbauer spectroscopic results on the alternatively prepared spin crossover coordination polymer Fe(3-Clpy)2Pd(CN)4 sample I agree with those of SQUID data. Mössbauer specrum at RT shows two diffrent doublets which correspond to the HS1(inner doublet) and HS2(outer doublet). The intensity of the HS1 doublet decreases on cooling to 78 K at the expense of a new one featuring the LS singlet. Almost 100 % of HS1 change to LS singlet due to iron(II) ions coordinated by four N atoms of cyano groups and two N atoms of 3-Clpy ligand in the sample I. The SQUID data of the sample I prepared by a new direct contact method are different from those of the already reported Fe(3-Clpy)2Pd(CN)4 sample. The differences of the SQUID data are associated with particle size effects in molecule spin crossover samples. 相似文献
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Ksenofontov V. Spiering H. Reiman S. Garcia Y. Gaspar A. B. Real J. A. Gütlich P. 《Hyperfine Interactions》2002,141(1-4):47-52
So far there has been no direct method to determine the spin state of molecules in dinuclear iron(II) compounds. The molecular fractions of high spin (HS) and low spin (LS) species have been deduced from magnetic susceptibility and zero field Mössbauer spectroscopy data irrespective of whether they belong to LS-LS, LS-HS and HS-HS pairs. However, the distinction of pairs becomes possible if Mössbauer measurements are carried out in an external magnetic field. The proposed method opens new possibilities in the study of spin crossover phenomena in dinuclear compounds.
相似文献20.
Alexander I. Nesterov Sergey G. Ovchinnikov Grigorii A. Iaroshenko 《Central European Journal of Physics》2013,11(7):894-903
In this paper we have analytically and numerically studied the dynamics of spin crossover induced by time-dependent pressure. We show that quasi static pressure, with a slow dependence on time, yields a spin crossover leading to transition from the high spin (HS) quantum system state to the low spin (LS) state. However, quench dynamics under shockwave load are more complicated. The final state of the system depends on the amplitude and pulse velocity, resulting in the mixture of the HS and LS states. 相似文献