La0.7Ca0.3Mn1-xCrxO3 (0.01≤x≤0.60)的低温热导

测量了锰位掺Cr系列巨磁阻多晶样品La0 .7Ca0 .3Mn1-xCrxO3(0 .0 1≤x≤ 0 .6 0 )的热导 ,实验温区 77～ 30 0K .随着Cr掺杂浓度x的增加 ,热导率κ(T)在所测温区内受到的压制变大 ,但当x =0 .6 0时 ,热导值却有较大的回升 ,显示了Cr掺入对晶格结构局部涨落的影响 .随温度降低 ,低掺杂样品在MI(金属 绝缘体 )转变点附近热导率κ(T)由dκ/dT >0变成dκ/dT<0 ,而高掺杂样品无MI转变 ,热导率随温度降低而减小 ,即dκ/dT >0 ,我们认为这是由载流子处于局域或巡游状态时与晶格的相互作用不同而导致的 .     

La1-xCaxMnO3材料的热导与电导

实验研究了两个典型掺杂的La1-xCaxMnO3(x=0.3和x=0.6)样品的热导率与电导率随温度的变化关系,测量温区为77－300K。样品的热导率与电导率的温度曲率之间有着很大的相似性：在高温部分,两个样品的电导率均随温度降低而下降,热导率也呈现类似的温度关系;在低温部分,两个样品的电导率呈现相反的温度关系,热导率的变化也截然不同。而且,在La1-xCaxMnO3多晶材料中,电导率很小,使得电子直接贡献的热导部分微乎其微。分析指出,La1-xCaxMnO3巨磁阻材料中由Jahn-Teller效应引起的晶格畸变,受到电子状态的直接影响和制约,从而对热导产生不同的作用。     

Spin Glass Behaviour and Spin-Dependent Scattering in La0.7Ca0.3Mn0.9Cr0.1O3 Perovskites

The magnetic, electrical and thermal transport properties of the perovskite La0.7Ca0.3Mn0.9 Cr0.1O3 have been investigated by measuring dc magnetization, ac susceptibility, the magnetoresistance and thermal conductivity in the temperature range of 5-300 K. The spin glass behaviour with a spin freezing temperature of 70 K has been well confirmed for this compound, which demonstrates the coexistence and competition between ferromagnetic and antiferromagnetic clusters by the introduction of Cr. Colossal magnetoresistance has been observed over the temperature range investigated. The introduction of Cr causes the ““double-bump““ feature in electrical resistivity ρ(T). Anomalies on the susceptibility and the thermal conductivity associated with the double-bumps in ρ(T)are observed simultaneously. The imaginary part of ac susceptibility shows a sharp peak at the temperature of insulating-metallic transition where the first resistivity bump was observed, but it is a deep-set valley near the temperature where the second bump in ρ(T) emerges. The thermal conductivity shows an increase below the temperature of the insulating-metallic transition, but the phonon scattering is enhanced accompanying the appearance of the second peak of double-bumps in ρ(T). We relate those observed in magnetic and transport properties of La0.7Ca0.3Mn0.9Cr0.1O3 to the spin-dependent scattering. The results reveal that the spin-phonon interaction may be of more significance than the electron (charge)-phonon interaction in the mixed perovskite system.