COLLAPSE OF ITINERANT ELECTRON MAGNETIC MOMENT UNDER HIGH FIELDS

巡回电子磁性最重要的特征之一是磁矩的大小本质上是随温度、压力和磁场而变化的。在本研究项目中，我们首先研究了在亚铁磁场作用下，Er&lt；1-x&gt；Lu_xCO_2体系巡回电子磁矩崩塌的可能性。其次，我们研究了自旋涨落对Fe Laves相化合物的热性质和输运性质的影响，其中一些Fe磁矩由于受挫效应而消失。本项目取得的成果如下：1.本课题取得的成果如下。在Er&lt；1-x&gt；Lu_xCO_2中，Co矩是由Er矩产生的分子场引起的。由于化合物是亚铁磁性的，所以外场方向与分子场方向相反。这意味着外加磁场降低了作用在Co原子上的有效磁场，因此Co磁矩在强磁场下崩塌，这必须被观察到是一种超磁转变。我们在15T附近观察到x=0.25时的超磁转变，在磁致伸缩测量中也发现了异常体积收缩。这些结果清楚地表明，Co磁矩在强磁场下崩塌。由于拓扑受挫而导致的Fe矩的消失导致了Hf_&lt；1-x&gt；Ta_xFe_2和Sc_&lt；1-x&gt；Ti_xFe_2的巨大自旋涨落。在临界浓度附近，我们观察到电子比热系数γ和电阻率温度依赖关系的T^2系数都显著增加。A/Gamma^2=常量。在自旋涨落理论的基础上，讨论了这种关系的起源。

One of the most important characteristics of itinerant electron magenetism is that the magnitude of magnetic moment is essentially variable with temperature, pressure and magnetic field. In this research project, first, we have studied the possibility of the collapse of itinerant electron magnetic moment by applying magnetic field using ferrimagnetic the Er_<1-x>Lu_xCo_2, system. Second, we have investigated the effects of spin fluctuations on the thermal and transport properties on Fe Laves phase compounds, in which some Fe moments disappear due to the frustration effect. The results obtained in this project are as follows.1. In Er_<1-x>Lu_xCo_2, the Co moment is induced by the molecular field from Er moments. Since the compound is ferrimagnetic, the direction of applied field is antiparallel to that of the molecular field. This means that the applied field decreases the effective field acting upon the Co atoms, and hence the Co moment collapses under high magnetic fields, which must be observed as a metamagnetic transition. We observed a metamagmetic transition for x=0.25 at around 15T.Anomalous volume shrinkage was also detected in the magnetostriction measurements. These results clearly indicates that the Co moment collapses under high magnetic fileds.2. The disappearance of Fe moments due to topological frustration leads to giant spin fluctuations in Hf_<1-x>Ta_xFe_2 and Sc_<1-x>Ti_xFe_2. At around the critical concentration, we observed significant enhancement of both the electronic specific heat coefficient, gamma, and the T^2 coefficient in the temperature dependence of the electrical resistivity, A.It has been found that these compounds show the Kadowaki-Woods relation. A/gamma^2=constant. The origin of this relation is also discussed on the basis of spin fluctuation theory.