Heavy Fermions in 3d Electron Systems

点击翻译按钮获取中文摘要

Recently, A heavy fermion, characterized by a huge electronic specific heat coefficient, gamma, has been found in 4f and 5f electron systems. Similar enhancement of gamma can be expected for 3d electron systems, when they show giant spin fluctuations. We have investigated the low temperature specific heat of several alloys and Laves phase compounds. The results are as follows.1. The nearly antiferromagnetic Y_<1-X> Sc_XMn_2 compounds show a giant gamma-value of 150mJ/K^2mol due to spin fluctuations. The enhancement factor, defined as gamma/gamma_b, where gamma_b is the theoretical gamma-value expected from the band calculation is about 15. This enhancement is comparable to that of a typical 5f heavy fermion UPt_3, 20.2. The nearly ferromagnetic Laves phase compounds, such as NbFe_2 and Y(Co_<1-X>Al_X)_2 also show an enhancement of gamma. The enhancement factor is at most 5, which is smaller than that of Y_<1-X>Sc_XMn_2.3. betaMn has no magnetic order down to 1.4 K. This metal is known to have a large gamma-value of 70mJ/K^2mol and is considered as a candidate for 3d heavy fermions. By substitution Al for Mn, we have found that the local moment character develops. This suggests that an electronic state in betaMn is on the verge for the onset of local moment, similarly to 4f and 5f heavy fermions. From these results, we conclude that antiferromagnetic spin fluctuations in a frustrative structure significantly enhances gamma-value in 3d electron systems.