Spin-glass behavior in a giant unit cell compound Tb₁₁₇Fe₅₂Ge₁₁₃.₈(₁).

In this paper we demonstrate evidence of a cluster spin glass in Tb₁₁₇Fe₅₂Ge₁₁₃.₈(₁) (a compound with a giant cubic unit cell) via ac and dc magnetic susceptibility, magnetization, magnetic relaxation and heat capacity measurements. The results clearly show that Tb₁₁₇Fe₅₂Ge₁₁₃.₈(₁)) undergoes a spin glass phase transition at the freezing temperature, ~38 K. The good fit of the frequency dependence of the freezing temperature to the critical slowing down model and Vogel-Fulcher law strongly suggest the formation of cluster glass in the Tb₁₁₇Fe₅₂Ge₁₁₃.₈(₁) system. The heat capacity data exhibit no evidence for long-range magnetic order, and yield a large value of Sommerfeld coefficient. The spin glass behavior of Tb₁₁₇Fe₅₂Ge₁₁₃.₈(₁) may be understood by assuming the presence of competing interactions among multiple non-equivalent Tb sites present in the highly complex unit cell.