Isotropic Γ6 Ground State in Caged Cubic Compound NdRu2Zn20

Abstract

The magnetic susceptibility χ, magnetization \(M\), and specific heat \(C\) were measured for the caged cubic compound NdRu2Zn20 at temperatures down to 0.5 K in magnetic fields \(H\) along the three principal crystallographic axes, [100], [110], and [111]. A ferromagnetic phase transition was observed at the Curie temperature \(T_{\text{C}}=1.9\) K in the temperature dependences of both χ(T) and \(C(T)\). Below \(T_{\text{C}}\), the magnetization curves \(M(H)\) show very weak magnetic anisotropy, and the \(C(T)\) curves in the fields along the three principal axes show no magnetic anisotropy both below and above \(T_{\text{C}}\). The easy direction of magnetization at 0.5 K changes from the [111] direction at 0 T to the [110] direction at 7 T. We analyzed these characteristic behaviors theoretically by taking into account the crystalline-electric-field energy, the magnetic exchange interaction, and the Zeeman energy. It was found that these features originate from the isotropic Γ6 ground state mixing with the magnetic Γ8(1) excited state. The temperature and magnetic field dependences of \(M(T,H)\) and \(C(T,H)\) are quantitatively in good agreement with this theoretical calculation.