用内耗技术研究La0.7Pb0.3MnO3巨磁电阻材料

用低频扭摆法在多功能内耗仪上测量了巨磁电阻材料La_0.7Pb_O.3MnO₃(LPMO)的温度内耗谱和弹性模量.结果表明,内耗峰位与测量频率无关,并且峰高与频率成反比,弹性模量在对应的内耗峰处有明显的转折,内耗峰表现为相变峰的特征.结合电阻和磁化率的测试,解释了内耗和电阻-温度曲线的双峰现象,高温内耗峰和高温电阻峰与居里温度有很好的对应,来源于顺磁半导体向铁磁金属的转变,低温内耗峰和磁化率的单调下降来源于铁磁相分离过程,而较大的低温电阻峰部分来源于相分离过程.

Properties of La0.7Pb0.3MnO3 Colossal Magnetoresistance Material Studied by the Internal Friction Technology

The internal frictions and elastic moduli of colossal magnetoresistance material La_0.7Pb_0.3MnO₃ were measured on multi-function internal friction apparatus with the low frequency torsion pendulum. The inverse proportionality of the peak height against the measurement frequency and the invariance of the peak position by changing frequencies are typical features of phase transition. The corresponding elastic modulus with a local minimum at internal friction peaks also characterizes the nature of phase transition. The relationships between double peaks of internal friction and the double peaks of electric resistance versus temperature were explaned by studying the colossal magnetoresistance effect and the susceptibility. The internal friction peak and resistance peak at higher temperatures correspond well with Curie temperature, ascribed to a transition from PMI to FMM. The internal friction peak at lower temperatures and the monotony descending of susceptibility may be interpreted as the phase separation originated from an inhomogeneous distributing of electric and magnetic phase, whereas the high resistance peak at lower temperatures may be partly from the phase separation.