Correlation between crystal structure and magnetic properties of Gd5(SixGe1-x)4 compounds

Abstract

Based upon the reported crystal structure data of Gd5(SixGe1-x)4 compounds, a possible correlation between the crystal structure and magnetic properties of the compounds is explored. An almost linear dependence of the ferromagnetic ordering temperature on a M-M (M = Si, Ge or a mixture of Si and Ge) bond length is derived within a first approximation. It is argued that the mechanism of the ferromagnetic coupling in the Gd5Si4-based (x>0.5) and Gd5Ge4-based (x0.2) solid solutions is the same as that in the intermediate phase Gd5(SixGe1-x)4 (0.24 x0.5), i.e. the ferromagnetic Gd-(Gd, M)-Gd blocks couple with each other via an M2 layer, regardless of their crystal structures at room temperature. The M-M bond length in the M2 layer is a crucial structural parameter governing the ferromagnetic ordering temperature of the compounds. The orthorhombic structure of the intermediate phase at low temperature is stabilized by the ferromagnetic exchange interaction.