Microstructural changes in Fe-doped Gd5Si2Ge2

Gd5Si2Ge2-based alloys can exhibit a giant magnetocaloric effect (GMCE); this gives them the potential for use in cooling technologies. It has also been reported that a small addition of iron reduces the hysteresis losses in Gd5Si2Ge2-based alloys, thus increasing the net refrigerating capacity. In this investigation, we have been the first to look at the effect on the microstructure and magnetic properties of Gd5Si2Ge2 resulting from a wide range of substitutions of Si by Fe. The macrostructures of the arc-melted buttons revealed some very unusual surface morphologies, and the analytical results revealed a gradual substitution of the Gd5(Si,Ge,Fe)4-type phase by a Gd5(Si,Ge,Fe)3-type phase and the presence of three grain-boundary phases, two of which contain substantial amounts of iron. The magnetic measurements indicated that larger amounts of iron reduced the hysteresis losses, but at the same time reduced the Curie temperatures to below lower values that would make the material useful in practice.