Abstract

We have analyzed the resistance of La_1.2Sr_1.8Mn_2(1 – z)O₇ single crystal in magnetic fields from 0 to 90 kOe in the ferromagnetic temperature range. The observed magnetoresistance of La_1.2Sr_1.8Mn₂O₇ is described based on the spin-polaron conduction mechanism. The magnetoresistance is determined by the change in the sizes and magnetic moment directions of magnetic inhomogeneities (polarons). It is shown that the colossal magnetoresistance is ensured by an increase (along the magnetic field) of the polaron linear size. It is found using the method for separating the contributions of different conduction mechanisms to the magnetoresistance that the contribution to the magnetoresistance from the orientation mechanism at 80 K in low magnetic fields is close to 50%. With increasing magnetic field, this contribution decreases and becomes small in fields exceeding 30 kOe. The comparable contributions to the conductivity from the orientational and spin-polaron mechanisms unambiguously necessitate the inclusion of both conduction mechanisms in the magnetoresistance calculations. We have calculated the temperature variation of the polaron size (in relative units) in zero magnetic field and in a magnetic field of 90 kOe.

中文翻译：

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基于铁磁温度范围内自旋极化子传导机理的La 1.2 Sr 1.8 Mn 2 O 7的大磁阻描述

摘要

我们已经分析了La _1.2 Sr _1.8 Mn _{2（1-  z）} O ₇单晶在铁磁温度范围内的0至90 kOe磁场中的电阻。La _1.2 Sr _1.8 Mn ₂ O _7的磁致电阻基于自旋极化子传导机制来描述。磁阻由磁不均匀性（极化子）的大小和磁矩方向的变化确定。示出了通过增大（沿磁场）极化子线性尺寸来确保巨大的磁阻。使用分离不同的传导机制对磁阻的贡献的方法发现，在低磁场下，在80 K时，取向机制对磁阻的贡献接近于50％。随着磁场的增加，该贡献减小，并且在超过30 kOe的场中变小。定向和自旋极化子机制对电导率的可比贡献无疑需要在磁阻计算中包括两种传导机制。我们已经计算了零磁场和90 kOe磁场中极化子尺寸的温度变化（相对单位）。