High temperature ferromagnetism in GdFe2Zn20: large, local moments embedded in the nearly ferromagnetic Fermi liquid compound YFe2Zn20

The RFe$_2$Zn$_{20}$ series manifests strongly correlated electron behavior for the non-magnetic R = Y member and remarkably high temperature, ferromagnetic ordering ($T_C$ = 86 K) for the local moment bearing R = Gd member (a compound that is less than 5% atomic Gd). In contrast, the isostructural RCo$_2$Zn$_{20}$ series manifests a more typical ordering temperature ($T_N$ = 5.7 K for GdCo$_2$Zn$_{20}$) and YCo$_2$Zn$_{20}$ does not show signs of correlated electron behavior. Studies of R(Fe$_x$Co$_{1-x}$)$_2$Zn$_{20}$ (R = Gd, Y), combined with bandstructure calculations for the end members, reveal that YFe$_2$Zn$_{20}$ is a nearly ferromagnetic Fermi liquid and that the remarkably high $T_C$ associated with GdFe$_2$Zn$_{20}$ is the result of submerging a large local moment into such a highly polarizable matrix. These results indicate that the RFe$_2$Zn$_{20}$ series, and more broadly the RT$_2$Zn$_{20}$ (T = Fe, Co, Ni, Mn, Ru, Rh, Os, Ir, Pt) isostructural family of compounds, offer an exceptionally promising phase space for the study of the interaction between local moment and correlated electron effects near the dilute R limit.