Correlation between crystal structure and magnetic properties of Gd-5(SixGe1-x)(4) compounds

Based upon the reported crystal structure data of Gd-5(SixGe(1-x))(4) compo unds, a possible correlation between the crystal structure and magnetic pro perties of the compounds is explored. An almost linear dependence of the fe rromagnetic ordering temperature on a M-M (M = Si, Ge or a mixture of Si an d Ge) bond length is derived within a first approximation. It is argued tha t the mechanism of the ferromagnetic coupling in the Gd5Si4-based (x > 0.5) and Gd5Ge4-based (x less than or equal to 0.2) solid solutions is the same as that in the intermediate phase Gd-5(SixGe(1-x))(4) (0.24 less than or e qual to x less than or equal to 0.5), i.e. the ferromagnetic Gd-(Gd, M)-Gd blocks couple with each other via an M-2 layer, regardless of their crystal structures at room temperature. The M-M bond length in the M-2 layer is a crucial structural parameter governing the ferromagnetic ordering temperatu re of the compounds. The orthorhombic structure of the intermediate phase a t low temperature is stabilized by the ferromagnetic exchange interaction.