Phase control studies in Gd5Si2Ge2 giant magnetocaloric compound

• Published in: Journal of alloys and compounds Vol. 529; pp. 89 - 95
• Main Authors: Belo, J.H., Pereira, A.M., Ventura, J., Oliveira, G.N.P., Araújo, J.P., Tavares, P.B., Fernandes, L., Algarabel, P.A., Magen, C., Morellon, L., Ibarra, M.R.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15-07-2012; Elsevier
• Subjects: Alloys; Annealing; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Conversion; Crystallographic aspects of phase transitions; Crystallography; Diffraction; Exact sciences and technology; Formation and annealing; Liquids; Magnetic phase transitions; Magnetic properties and materials; Magnetic transitions; Magnetically ordered materials: other intrinsic properties; Magnetocaloric compounds; Magnetocaloric effect, magnetic cooling; Optimization; Physics; Magnetic phase transitions; 61.50.Ks; 75.30.Sg; Magnetocaloric compounds; Crystallographic aspects of phase transitions; 61.72.Cc; Formation and annealing; 75.30.Kz; Annealing; Magnetization; XRD; Magnetic transitions; Gadolinium Germanides; Magnetocaloric effects; Giant magnetocaloric effect; Gadolinium silicides
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2012.02.164

► Study of time dependence of O(I) to M phase. ► Determination of the optimal annealing time. ► New method for phase amount estimation (O(I) and M). ► Effect of annealing on the MCE. ► Analysis of the nature of the magnetic transition through the Arrot plot representation.
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=1473K) 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 80–120min at T=1473K followed by a rapid quenching to liquid N2. Furthermore, an increase up to ∼50% of the magnetocaloric effect was obtained for the sample annealed during 120min.