Magnetic properties ofRFe2Zn20andRCo2Zn20(R=Y,Nd,Sm,Gd–Lu)

Abstract

Magnetization, resistivity, and specific heat measurements were performed on solution-grown single crystals of $R{\text{Fe}}_{2}{\text{Zn}}_{20}$ and $R{\text{Co}}_{2}{\text{Zn}}_{20}$ $(R=\text{Y},\text{Nd},\text{Sm},\text{Gd-Lu})$. Whereas ${\text{LuCo}}_{2}{\text{Zn}}_{20}$ and ${\text{YCo}}_{2}{\text{Zn}}_{20}$ manifest unremarkable metallic behavior, ${\text{LuFe}}_{2}{\text{Zn}}_{20}$ and ${\text{YFe}}_{2}{\text{Zn}}_{20}$ display behaviors such as characteristic of nearly ferromagnetic Fermi liquids. When the well-defined $4f$ local moments $({\text{Gd}}^{3+}{\text{-Tm}}^{3+})$ are embedded into this strongly polarizable host, they manifest enhanced ferromagnetic ordering and the values of ${T}_{\text{C}}$ for $R{\text{Fe}}_{2}{\text{Zn}}_{20}$ $(R=\text{Gd-Tm})$ scale with the de Gennes factor. In addition, data on the $R{\text{Fe}}_{2}{\text{Zn}}_{20}$ compounds indicate a small crystal electric field (CEF) effect compared with the interaction energy scale. On the other hand, the local moment bearing members of $R{\text{Co}}_{2}{\text{Zn}}_{20}$ $(R=\text{Nd},\text{Sm},\text{Gd-Tm})$ manifest weak magnetic interactions and the magnetic properties for $R=\text{Dy-Tm}$ 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 with its cubic point symmetry. 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 $R=\text{Tb-Ho}$, the CEF splitting scale is smaller than their ${T}_{\text{C}}$ values, whereas for ${\text{ErFe}}_{2}{\text{Zn}}_{20}$ and ${\text{TmFe}}_{2}{\text{Zn}}_{20}$ the $4f$ electrons lose part of their full Hund's rule ground state degeneracy above ${T}_{\text{C}}$. ${\text{YbFe}}_{2}{\text{Zn}}_{20}$ and ${\text{YbCo}}_{2}{\text{Zn}}_{20}$ manifest typical but distinct heavy fermion behaviors associated with different Kondo temperatures.