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1.
通过对Eu2-xPbxRu2O7(x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0和1.8)系列样品的结构、电阻和磁化率的观测,结果发现,随着Pb替代浓度x值的增加,样品的电阻率逐渐减小,系统在x=0.8附近发生了金属-绝缘体(M-I)相变;Ru4+的局域磁矩及其自旋玻璃冻结温度TG也随之降低. 在该体系中,Pb2+对Eu3+的部分替代使样品中载流子浓度增加,Pb的6p能带与Ru 4d电子的T2g能带混合,能带得以拓宽,Ru 4d电子的巡游性增强,导致该体系物性的系列变化. 相似文献
2.
通过晶体结构、电学和磁学测量,我们系统地研究了Fe掺杂的烧绿石Bi_(2-x)Fe_xIr_2o_7(x=0.1,0.2,0.3,0.4)样品.X射线衍射证实了高结晶的Bi_(2-x)Fe_xIr_2o_7保持立方结构.样品体系显示出金属-绝缘体转变:当x=0.1,转变温度为63.870K.随着Fe含量的增加,转变温度呈上升趋势.掺杂样品显示出增强的反铁磁性,并随着Fe掺杂增加,反铁磁性增强.当掺杂量增加到0.3时,样品发生类自旋玻璃态转变. 相似文献
3.
拓扑电子材料因为具有非平庸的拓扑态,所以会展现出许多奇异的物理性质.本文通过第一性原理计算对应变调控下的烧绿石三元氧化物Tl2Ta2O7中的拓扑相变进行了研究.首先分析了原子轨道投影能带,发现体系费米能级附近O原子的(px+py)与pz轨道发生了能带反转,再构造了紧束缚模型计算得到体系的Z2拓扑不变量确定了其拓扑非平庸性,最后研究了表面态等拓扑性质.研究发现未施加应变的Tl2Ta2O7是一个在费米能级处具有二次能带交叉点的半金属,而平面内应变会破缺晶体对称性进而使体系发生拓扑相变.当对体系施加–1%的压缩应变时,它会转变为狄拉克半金属;当对体系施加1%的拉伸应变时,体系相变为拓扑绝缘体.本研究对于在三维材料中调控拓扑相变有着较重要的指导意义,并且为低能耗电子器件的设计提供了良好的材料平台. 相似文献
4.
通过对La0.3Ca0.7Mn1-xVxO3(x=0.05,0.10,0.134,0.20)体系的M-T曲线、ρ-T曲线、ESR谱的测量,研究了Mn位掺V对La0.3Ca0.7MnO3体系电荷序和自旋序的影响.结果表明,当0.05≤x≤0.134时, 体系存在电荷有序(CO)相,其自旋序随温度降低发生顺磁(PM)-电荷有序(CO)-反铁磁(AFM)变化.当x=0.20时,CO相逐步融化,在40 K发生自旋玻璃转变,表现出再入型的自旋玻璃行为,低温下的基态存在着多种复杂的磁相互作用之间的竞争机理.
关键词:
电荷有序
自旋序
相分离
再入型自旋玻璃行为 相似文献
5.
采用固相反应法制备了SrMn0.5Fe0.5O3陶瓷样品,并对样品的晶体结构,磁性和离子价态进行了系统的表征与分析. X射线衍射谱的Rietveld拟合表明样品属于理想的立方钙钛矿型结构,Mn离子和Fe离子随机占据B位的O八面体中心. X射线光电子能谱表明Mn离子为+3和+4的混合原子价态,Fe离子为+3价. 样品在大于230K的高温区域呈现Curie顺磁特性,在小于230 K的低温区域样品表现出自旋玻璃态行为,这种特性源于Mn离子和Fe离子之间的交换作用及自身价态和分布的不均匀性. 由于Fe3+离子占据O八面体的中心,对顺磁区的Mssbauer谱测量表现为四级分裂.
关键词:
晶体结构
价态
顺磁
自旋玻璃态 相似文献
6.
采用固相反应法制备了SrMn0.5Fe0.5O3陶瓷样品,并对样品的晶体结构,磁性和离子价态进行了系统的表征与分析. X射线衍射谱的Rietveld拟合表明样品属于理想的立方钙钛矿型结构,Mn离子和Fe离子随机占据B位的O八面体中心. X射线光电子能谱表明Mn离子为+3和+4的混合原子价态,Fe离子为+3价. 样品在大于230K的高温区域呈现Curie顺磁特性,在小于230 K的低温区域样品表现出自旋玻璃态行为,这种特性源于Mn离子和Fe离子之间的交换作用及自身价态和分布的不均匀性. 由于Fe3+离子占据O八面体的中心,对顺磁区的Mssbauer谱测量表现为四级分裂. 相似文献
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在采用固相反应法成功制备单相Na0.75Co1-xRuxO2(0≤x≤0.5)样品的基础上,对其结构、输运性质和磁性质进行了系统研究.结果表明, x≤0.5的样品仍保持单相,样品的晶格参数随着Ru替代浓度x值的增加逐渐增大,说明在该体系中,Ru能均匀地替代Co.对于x=0的样品,在整个测量温区内,其电阻率-温度关系呈现典型的金属行为; x=0.01样品在T=37K附近发生了金属-绝缘体相变;而x≥0.02的所有样品,整个测量温区内均为半导体.与x=0样品相比较,x=0.1样品在30K时的电阻率增大了5个数量级.我们认为该体系在x=0.01附近发生的金属-绝缘体(MI)相变,起源于CoO2层的无序导致的电子的Anderson局域化.对于所有样品,在2K以上均没有观测到长程磁有序,其磁化率在100 K以上均满足居里-外斯定律,同时对该体系的磁化率结果进行了详细讨论. 相似文献
10.
在采用固相反应法成功制备单相Na0.75Co1-xRuxO2(0≤x≤0.5)样品的基础上,对其结构、输运性质和磁性质进行了系统研究.结果表明,x≤0.5的样品仍保持单相。样品的晶格参数随着Ru替代浓度x值的增加逐渐增大,说明在该体系中,Ru能均匀地替代Co.对于x=0的样品,在整个测量温区内,其电阻率-温度关系呈现典型的金属行为;x=0.01样品在T=37K附近发生了金属-绝缘体相变;而x≥0.02的所有样品,整个测量温区内均为半导体.与x=0样品相比较.x=0.1样品在30K时的电阻率增大了5个数量级.我们认为该体系在x=0.01附近发生的金属-绝缘体(MI)相变,起源于CoO2层的无序导致的电子的Anderson局域化.对于所有样品,在2K以上均没有观测到长程磁有序。其磁化率在100K以上均满足居里-外斯定律,同时对该体系的磁化率结果进行了详细讨论. 相似文献
11.
Abstract Luminescence spectra from Eu3 + ion in B-type (monoclinic) 2O3 powder have been recorded at room temperature as a function of pressure using a diamond anvil cell. Changes in the spectral pattern of the Eu3 + ion emission at about 4 GPa indicated that a phase transition to the A-type (hexagonal) structure had taken place. Upon release of the applied pressure, the B-type structure was regained with hysteresis. The spectral shifts with pressure have been used to study the effect of pressure on the spin-orbit interaction of the 4f electrons in the Ed + ion. The relationship between the relative changes in the spin-orbit coupling constant, ζ4f, and the volume accompanying the phase transition is also discussed. 相似文献
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13.
Abstract X-ray powder diffraction measurements for YBa2Cu3O7-y and NdBa2Cu3O7-y were made at the intense synchrotron radiation source under high pressure up to 5 GPa. These samples were wrapped tightly in platinum foil to avoid deoxidizing atmosphere. The orthorhombic to tetragonal transition temperature increases with pressure in both samples. These results are discussed on the basis of the disordering of the oxygen atoms on the chain sites. 相似文献
14.
针对NiS2-xSex系统在x=1.00附近发生的反铁磁量子相变,制备了一系列NiS2-xSex(x=0.96, 0.98, 1.00, 1.05, 1.10和1.20)多晶样品,对其结构、磁性质和电阻率进行了系统的观测.结果发现:样品磁化率-温度关系呈现典型的强关联电子系统特征;与铜氧化物超导体相类似,它们的电阻率-温度关系在很宽的温
关键词:
量子相变
反铁磁自旋涨落
2-xSex体系')" href="#">NiS2-xSex体系 相似文献
15.
Previous work on Ba2TiGe2O8 crystals has shown an unusual low-temperature (~ 223 K on cooling, ~ 273 K on heating) phase transition. Precession x-ray photographs on Ba2TiGe2O8 single crystals show an incommensurate modulation along b*, and, for the first time, also along a*. Single crystal intensity data confirm the average structure in space group Cmm2. There is positional disorder in the pyrogermanate groups, and this is the probable cause for the modulated structure. The low-temperature phase transition is proposed to be a lock-in transition, with the modulation along a* locking in at a value of 1/3. Several properties, as well as other unusual features of the low-temperature phase transition, are discussed in light of the proposed lock-in transition. Domain studies show that the ferroelastic domains are unstable in the low-temperature phase. 相似文献
16.
Abstract Luminescence spectra from Eu3+ ion in C-type Eu2O3 under high pressures have been obtained. The spectral shifts can be used to study the effect of pressure on the spin-orbit and the Coulomb interactions of the 4f electrons, which are correlated with expansion of the 4f-electron wave functions. This expansion with the application of pressure results in both the variation of the electronegativity and radius of the Eu3+ ion and, ultimately, the phase transformation from C-to B-type Eu2O3. Therefore, core 4f-electrons can thus be thought of as quasivalence electrons. 相似文献
17.
Abstract With increasing X on Ca1-xSrxF2 mixed crystals doped with Eu2+ (4f65d) ions, the absorption peak shifted linearly to that of SrF2:Eu, while the luminescence one moved parabolically with a minimum at around x=0.5. The linewidth broadened nearly twice as large as that of CaF2 in the vicinity of x=0.5 and subsequently renarrowed for x > 0.5. The temperature dependences of the luminescence intensity and life time revealed that the nonradiative activation energy has a minimum of 0.40 eV around x=0.5. From the calculated result of the lineshape, these non-linear behaviors against x were explained by adjusting the electron-phonon coupling strength. 相似文献
18.
Hydrostatic pressure has negligible effect on the resistivity anomaly and thec
H
/a
H
ratio of Ti2O3. The results are consistent with the band-crossing mechanism wherein the a
T
and e
T
bands cross as thec
H
/a
H
ratio increases. 相似文献