Formation of completely miscible solid-solution Gd5(Si1−xGex)4 induced by ferromagnetic exchange interaction

The crystal structure and magnetic properties of Gd-5(Si1-xGex)(4) compounds (0 less than or equal to x less than or equal to 1.0) are investigated by means of temperature dependent X-ray powder diffraction and magnetic measurements. A crystallographic and magnetic phase diagram of the pseudobinary system Gd5Si4-Gd5Ge4 is constructed. An intriguing observation is that Gd-5(Si1-xGex)(4) alloys form a completely miscible solid-solution at low temperature (< T-C), crystallizing in the Gd5Si4-type structure as indicated by the well-defined linear dependence of lattice parameters on germanium concentration x, and decomposing into three partially miscible solid-solutions above the Curie temperature, i.e. Gd5Si4 based (x < 0.5), Gd5Ge4 based (x greater than or equal to 0.8) and Gd5Si2Ge2 based (0.5 less than or equal to x < 0.8) solid-solutions, This unusual feature can be understood by taking into account competing effects of ferromagnetic exchange interaction and lattice strain in the solid-solution. (C) 2001 Elsevier Science B.V. All rights reserved.