Phase control studies in Gd5Si2Ge2 giant magnetocaloric compound

A systematic set of annealings on arc-melted synthesized Gd5Si2Ge2 sample was performed. Through powder X-ray diffraction (XRD) and magnetometry measurements we monitored the effect of varying the annealing time with constant temperature (T = 1473 K) on the formation of the monoclinic (M) crystallographic phase fraction, which is the one responsible for the giant magnetocaloric effect (GMCE) in this compound. The conversion of the orthorhombic O(I) crystallographic phase into M was achieved, resulting in a significant increase of the M mass fraction. Such conversion led to a change in the magnetic transition nature, evolving from a second to a first order transition for the as-cast and annealed samples, respectively. An optimal annealing time range for the M phase conversion was identified to be within 80-120 min at T = 1473 K followed by a rapid quenching to liquid N-2. Furthermore, an increase up to similar to 50% of the magnetocaloric effect was obtained for the sample annealed during 120 min. (C) 2012 Elsevier B.V. All rights reserved.