COLLAPSE OF ITINERANT ELECTRON MAGNETIC MOMENT UNDER HIGH FIELDS

巡游电子磁性的一个重要特征是磁矩的大小随温度、压力和磁场的变化而变化。在本研究计划中，我们首先研究了在亚铁磁Er_ Lu_xCo_2系统中施加磁场时，巡游电子磁矩坍缩的可能<1-x>性。其次，我们研究了自旋涨落对铁Laves相化合物的热性质和输运性质的影响，其中一些铁矩由于阻挫效应而消失。本项目取得的主要成果如下：1.在Er_ Lu_xCo_2中<1-x>，Co矩是由Er矩的分子场诱导的。由于化合物是亚铁磁性的，所施加的场的方向与分子场的方向反平行。这意味着施加的场降低了作用在Co原子上的有效场，因此Co磁矩在高磁场下塌陷，这必须被观察为变磁跃迁。在15 T附近观察到了x=0.25的亚磁性转变，在磁致伸缩测量中也发现了异常的体积收缩。这些结果清楚地表明Co磁矩在高磁场下发生了坍缩.在Hf_ Ta_xFe_2和Sc_ Ti_xFe_2中，由于拓扑阻挫导致Fe磁矩的消失，导致了自旋的巨大涨落<1-x><1-x>.在临界浓度附近，我们观察到电子比热系数γ和电阻率A的温度依赖性中的T^2系数显著增强。已经发现，这些化合物显示出Kadowaki-Woods关系。A/gamma^2=常数。本文还从自旋涨落理论出发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.