Microstructure and magnetocaloric effect in Gd5Si2(Ge1−xGax)2 alloys

Crystal structure of the phases, microstructure and magnetocaloric effect were investigated in Gd5Si2(Ge1−xGax)2 alloys with x = 0, 0.01, 0.02 and 0.03. The phase identification and compositional analysis were carried out by a combination of X-ray diffraction, scanning electron microscopy and electron probe micro-analysis. The Gd5Si2Ge2-type matrix phase having an orthorhombic structure co-exists with Gd5Ge3-type and GdGe-rich phases. Ga was found to have preferentially partitioned to the orthorhombic Gd5Si2Ge2-type matrix phase. Magneto-structural transition temperatures determined from differential scanning calorimetry and thermo-magnetic techniques revealed that Ga substituted alloys exhibit only magnetic transition unlike parent Gd5Si2Ge2 alloy which displays both structural and magnetic transitions. A maximum magnetic entropy change (ΔS)M of 7.0 J/kg K was obtained in x = 0 alloy for a magnetic field change of 2 T and its magnitude was lower in the Ga substituted alloys.