COLLAPSE OF ITINERANT ELECTRON MAGNETIC MOMENT UNDER HIGH FIELDS

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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.