Magnetic properties of RFe$_2$Zn$_{20}$ and RCo$_2$Zn$_{20}$(R = Y, Nd, Sm, Gd - Lu)

TL;DR

This study investigates the magnetic, electronic, and specific heat properties of RFe2Zn20 and RCo2Zn20 compounds, revealing nearly ferromagnetic behavior in Fe-based series, magnetic ordering influenced by local moments, and heavy Fermion behavior in Yb-based compounds.

Contribution

It provides a comprehensive analysis of magnetic interactions, crystal electric field effects, and heavy Fermion behavior across RFe2Zn20 and RCo2Zn20 series, highlighting similarities and differences between Fe and Co compounds.

Findings

Fe-based compounds show nearly ferromagnetic behavior.

Gd-Tm RFe2Zn20 compounds exhibit ferromagnetic ordering scaling with de Gennes factor.

Yb compounds display heavy Fermion behavior with distinct Kondo temperatures.

Abstract

Magnetization, resistivity and specific heat measurements were performed on single crystals of RFe$_2$Zn$_{20}$ and RCo$_2$Zn$_{20}$(R = Y, Nd, Sm, Gd - Lu). Whereas LuCo$_2$Zn$_{20}$ and YCo$_2$Zn$_{20}$ manifest unremarkable, metallic behavior, LuFe$_2$Zn$_{20}$ and YFe$_2$Zn$_{20}$ manifest behaviors characteristic of nearly ferromagnetic Fermi liquids. When the well defined $4f$ local moments (Gd$^{3+}$ - Tm$^{3+}$) were embedded into this strongly polarizable host, they all manifest enhanced, ferromagnetic ordering and the values of $T_{\mathrm{C}}$ for RFe$_2$Zn$_{20}$ (R = Gd - Tm) scale with the de Gennes factor. In addition, the data on the RFe$_2$Zn$_{20}$ 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 RCo$_2$Zn$_{20}$ (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 $T_{\mathrm{C}}$ values, whereas for ErFe$_2$Zn$_{20}$ and TmFe$_2$Zn$_{20}$ the $4f$ electron loses part of its full Hund's rule ground state degeneracy above $T_{\mathrm{C}}$. YbFe$_2$Zn$_{20}$ and YbCo$_2$Zn$_{20}$ manifest typical, but distinct heavy Fermion behaviors associated with different Kondo temperatures.