Ca缺位型稀土金属氧化物La_(0.65)Ca_xMnO_3的磁电特性分析

制备了 Ca缺位型稀土金属氧化物 L a0 .6 5Cax Mn O3,并对磁性及电输运特性进行了研究。发现随 Ca缺位的增加 ,材料的晶胞体积增大 ,但居里温度却减小 ,铁磁相互作用减弱。材料的金属 -半导体转换峰值温度 Ttran随 Ca缺位程度的增加相应减小而电阻峰值却增大 ,作者用极化子电阻模型拟合了金属 -半导体转换峰温度 Ttran以上的电阻温度依赖关系 ,发现 Ca缺位材料电阻的增大可能与局域波函数的衰减长度减小有关。还同时利用迪尼模型在 10 0 K～ 3 0 0 K温区内 ,分析计算了材料电阻随温度的变化关系 ,发现磁交换能和电 -声相互作用能对极化陷阱能的贡献在有 Ca缺位时比无缺位时均有所增大。极化陷阱能的增高减低了载流子的活动能力。同时还对 Ca含量、Mn+ 3/ Mn+ 4含量、氧缺位量存在的关系进行了讨论。

Analyses of Magnetic and Electric Behaviors in La_(0.65)Ca_xMnO_3 Rare Earth Oxides with Ca Vacancies

The rare earth oxide La_ 065Ca_ x MnO_3 with Ca vacancies were prepared, and the magnetic and electric transport behaviors were investigated. The experimental results show that with increasing Ca vacancies, the unit cell volume of La_ 065Ca _x MnO_3 increases, but the Curit temperature decreases and the ferromagnetic interaction is suppressed. The temperature of metal semiconductor transition, T _ tran, decreases, and the peak value of resistance increases with increasing Ca vacancies. The temperature dependence of the resistance above metal-semiconductor transition temperature is simulated based on the polaron-resistance model. The simulated results indicate that the increment of resistance for materials with Ca vacancies is associated with the decrement of decay length of local wave function. Meanwhile, the temperature dependence of resistance from 100 K to 300 K is calculated based on the Dionne model. The calculated data show that the polaron-trapping energy resulted from both the magnetic exchange interaction and the electron-phonon interaction enhance with increasing Ca vacancies, which reduces the active ability of the current carrier. The relationships among Ca content, amount of ions Mn 3+/Mn 4+ and oxygen vacancies in La_ 065Ca _x MnO_3 are also discussed in details.