Magnetic and electrical transport properties of Dy xGd 5−xSi 2Ge 2 ( x=0.0, 1.5, 2.5, 3.0, 3.5, 4.5 and 5.0) compounds

Abstract

Effect of Dy substitution at the Gd-site on the magnetic and electrical transport properties of the giant magnetocaloric effect material, Gd 5Si 2Ge 2, has been explored. At room temperature, Dy x Gd 5− x Si 2Ge 2 ( x⩽3.5) compounds have the monoclinic Gd 5Si 2Ge 2-type crystal structure (Space group P2 1/a), while those with x>3.5, have orthorhombic Sm 5Ge 4-type structure (Space group Pnma). The Dy substitution contracts the unit cell and also reduces the monoclinic distortion. The compound Gd 5Si 2Ge 2 orders ferromagnetically at 276 K; with increasing Dy substitution, the magnetic transition temperature decreases ( T N=56 K for Dy 5Si 2Ge 2) and the nature of magnetic coupling becomes antiferromagnetic in Dy-rich end. The electrical resistivity shows a marked drop near T C/ T N. The thermoelectric power undergoes a slope change in the vicinity of magnetic transition and the signature of phonon and magnon drag effects is observed at low temperatures. Thus progressive Dy substitution in Gd 5Si 2Ge 2 leads to a class of materials with interesting magnetic ground states, with magnetic ordering temperatures spanning from 56 to 276 K.