Magnetic properties of RFe2Zn20 and RCo2Zn20(R = Y, Nd, Sm, Gd - Lu)
Abstract
Magnetization, resistivity and specific heat measurements were performed on single crystals of RFe2Zn20 and RCo2Zn20(R = Y, Nd, Sm, Gd - Lu). Whereas LuCo2Zn20 and YCo2Zn20 manifest unremarkable, metallic behavior, LuFe2Zn20 and YFe2Zn20 manifest behaviors characteristic of nearly ferromagnetic Fermi liquids. When the well defined 4f local moments (Gd3+ - Tm3+) were embedded into this strongly polarizable host, they all manifest enhanced, ferromagnetic ordering and the values of TC for RFe2Zn20 (R = Gd - Tm) scale with the de Gennes factor. In addition, the data on the RFe2Zn20 compounds indicate a small crystal electronic field (CEF) effect, compare with the interaction energy scale. On the other hand, the local moment bearing members of RCo2Zn20 (R = Nd, Sm, Gd - Tm) manifest weak magnetic interactions and the magnetic properties for R = Dy - Tm members are strongly influenced by the CEF effect on the R ions. The magnetic anisotropy and specific heat data for the Co series were used to determine the CEF coefficient of R ion in the cubic coordination. These CEF coefficients, determined for the Co series, are consistent with the magnetic anisotropy and specific heat data for the Fe series, which indicates similar CEF effects for the Fe and Co series. Such analysis, combined with specific heat and resistivity data, indicates that for R = Tb - Ho, the CEF splitting scale is smaller than their TC values, whereas for ErFe2Zn20 and TmFe2Zn20 the 4f electron loses part of its full Hund's rule ground state degeneracy above TC. YbFe2Zn20 and YbCo2Zn20 manifest typical, but distinct heavy Fermion behaviors associated with different Kondo temperatures.
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