摘要
通过电阻率、磁化曲线和电子自旋共振谱 (ESR)的测量 ,对超大磁阻材料La2 /3Ca1 /3MnO3的绝缘体 金属 (I M)转变过程进行了研究。在磁场作用下 ,高温顺磁相的电阻率与绝热小极化子跃迁模式 [ρ～BTexp(Ea/kT) ]相吻合 ,低温铁磁相的电阻率与单磁振子散射模式 ( ρ～ρ0 +AT2 )相吻合 ,这意味着在I M转变期间 ,小极化子和巡游载流子是共存的。基于磁有序过程引发小极化子退局域这一认识 ,用两相模型定量描述I M转变期间的输运行为 ,在不同磁场下电阻率的计算结果与实验数据非常接近 ,有力证明了I
The insulator metal transition in colossal magnetoresistance material La 2/3 Ca 1/3 MnO 3 was studied by electrical transport, magnetization and electron spin resonance (ESR) measurements. The resistivity in different applied magnetic fields can be well fitted by adiabatic small polaron hopping model ( ρ～BT exp( E a/ kT )) in high temperature paramagnetic phase, and by single magnon scattering process ( ρ～ρ 0+ AT 2) in low temperature ferromagnetic phase. Around the insulator metal transition, the ESR signal shows a crossover from paramagnetic resonance line to ferromagnetic resonance line, which implies a coexistence of localized small polarons and itinerant carriers during the insulator metal transition. Based on the concept of “small polaron collapse”, i. e., the violent delocalization of small polarons triggered by the occurrence of ferromagnetic order, a two phase model was proposed to quantitatively describe the electrical transport behavior across the insulator metal transition. The calculations of resistivity in different applied magnetic fields have close trends with the experimental data, which strongly proves that the insulator metal transition results from the collapse of small polarons and two distinctive transport processes coexist during the transition.
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2004年第4期613-616,共4页
Chinese Journal of Rare Metals
基金
国家自然科学基金重点项目 ( 1993 40 0 3 )
国家重点基础研究发展规划项目 ( 0 0 1CB610 60 4)
关键词
凝聚态物理
绝缘体
金属转变
极化子
退局域
稀土
coherence physics
insulator-metal transition
small polaron
collapse
rare earths
