电荷有序态La_(0.25)Ca_(0.75)MnO_3的红外光学特性分析

Infrared optical analysis of charge-ordered La_(0.25)Ca_(0.75)MnO_3

采用高温固相法制备了电荷有序态锰氧化物La0.25Ca0.75MnO3样品.从297?78K每隔10K测试了该样品的变温红外反射谱,发现在240K时红外反射谱有了显著的转变.这与该样品的磁化强度-温度关系曲线所呈现的相变温度点相一致.磁性测量表明该样品在240K发生了高温顺磁相到低温反铁磁相的转变.此外,红外光电导还揭示了该样品中在160K温度处有新的反常现象,可能是在此温度附近存在低能激发态.从反铁磁转变、电荷有序态和晶格畸变等方面对观察到的实验结果进行了分析和讨论.

The charge-ordered manganese oxide La0.25Ca0.75MnO3 is sintered by a solid-state method.The infrared reflectivity of this sample is studied over a broad range of temperatures 78？297 K with an interval of 10 K,and the obvious transition is found at 240 K.This transition temperature is in agreement with the phase transition temperature revealed with the magnetization measurements.Magnetism measurement indicates that the sample has a high temperature paramagnetic-low temperature antiferromagnetic transition at 240 K.In addition,the optical conductivity discloses that there is a new abnormal phenomenon appears at 160 K,around which there are low-energy excitation states.The analysis and discussion are elaborated on experimental results in terms of antiferromagnetic transition,charge-order and lattice distortion.