稀磁合金中“电阻极大”现象的双杂质散射理论

本文基于s-d相互作用,考虑杂质之间存在RKKY相互作用,提出了一种新的双杂质散射模型。按照这个模型,当一个杂质作自旋翻转散射时,由于杂质之间存在着RKKY关联,它的自旋作为内部自由度会受到限制。由于这种关联,抑制了杂质的自旋翻转散射,结合Kondo的logT项,能形成电阻极大。本文计算了所有可能的“DIS”图(双杂质自能图),在Kondo电阻公式中加入了A/(T₀²—T²)这样的项。其中A是一个正常数。T₀是一个临界温度。当T≤T₀时,这个公式不再有意义。这个理论和已有的分子场理论在本质上是不同的.因为它并不依赖于合金中的磁有序.因此当T≥T_c时(T_c是磁有序转变温度),这种机制仍起作用,但分子场理论则不行.这是一种顺磁效应.我们和Cd-Mn(杂质浓度从0.01到0.1at./0)的实验曲线进行了比较,发现符合得很好.最后,我们认为即使在极低浓度下这种机制也是消除Kondo logT发散的主要原因. 关键词：

THE DOUBLE IMPURITIES SCATTERING THEORY FOR "THE RESISTANCE MAXIMUM" PHENOMENA IN THE DILUTE MAGNETIC ALLOYS

Based on s-d interaction, we consider RKKY interaction existing between two magnetic impurities, and propose a new double impurities scattering model. According to this model, when an impurity spin makes spin flip scattering, its spin as an inner free degree will be confined by other impurities' spin, where the RKKY correlation exists between them. Because of this correlation, it will suppress its spin flip scattering. This suppression, coupled with the Kondo logT term, causes a local maximum. In this paper we have calculated all possible "DIS" diagrams (the double impurities self-energy diagrams) and found a term A/(T₀²-T²) contribute to the Kondo resistance, where A is a positive constant, T₀ is some critical temperature. When T≤T₀, this formula is meaningless. This theory is essentially different from the previous molecular field theory. Because it does not depend on the magnetic order in alloys, so, when T≥T_c (T_c is magnetic phase transion temperature), this mechanism still works but the molecular field theory does not. This mechanism is a paramagnetic effect. We have compared this theory with experimental curves of Cd-Mn (its impurity density is 0.1～0.01 at.%). We find that the agreement with experiments is good. Finally, we consider that this mechanism is the main reason to quench the Kondo log T divergence even for very dilute magnetic alloys in low temperature.