Journal of Magnetism and Magnetic Materials 272–276 (2004) 848–849 On the determination of the phase composition of the Gd 5 Ge 2 Si 2 alloy S. Gama a, *, C.S. Alves b , A.A. Coelho a , C.A. Ribeiro a , A.I.C. Persiano c , Dailto Silva a a Instituto de F! ısica Gleb Wataghin, Universidade Estadual de Campinas – UNICAMP, Caixa Postal 6165, IFGW-DFA, Campinas SP 13083-970, Brazil b Centro de Tecnologia de Maring ! a, Universidade Estadual de Maring ! a – UEM, Maring ! a, PR, Brazil c Instituto de F! ısica – Centro de Ci # encias Exatas, Universidade Federal de Minas Gerais – UFMG, Belo Horizonte, MG, Brazil Abstract Samples of the compound Gd 5 Ge 2 Si 2 were prepared by arc-melting and heat-treated at high temperatures. They were characterized by metallographic analysis and magnetization measurements. The observed phases were characterized using energy dispersive spectroscopy and subsequently using wavelength dispersive spectroscopy. The results indicate an imbalance in the proportion of Si and Ge for both observed phases, and good magnetocaloric properties for the heat-treated samples. r 2004 Elsevier B.V. All rights reserved. PACS: 75.30.Sg; 81.05.Bx Keywords: Magnetocaloric effect; Gd 5 Ge 2 Si 2 ; Energy dispersive spectroscopy; Wavelength dispersive spectroscopy 1. Introduction Since the discovery of the giant magnetocaloric effect (GME) on the family Gd 5 ðSi 1x Ge x Þ 4 [1] several studies aimed to clarify the phase relations around the composition x ¼ 0:5 [2,3], which were first disclosed by Holtzberg et al. [4]. It is implicitly assumed that Ge substitutes for Si without restrictions, unless for a miscibility gap occurring at high Ge concentra- tions [3,4]. Here we discuss our results on the composi- tion determinations of the phases present in our samples, using both energy dispersive spectroscopy (EDS), and wavelength dispersive spectroscopy (WDS) coupled to an electron probe microscope analyzer (EPMA). 2. Experimental procedure The Gd 5 Ge 2 Si 2 alloys were arc melted using 99:9 wt% Gd and electronic grade Si and Ge. Mass loss in the melting were always less than 0.5%. Heat treatments were done at 1600  C in a RF furnace up to 48 h: The alloys were metallographically prepared together with pieces of Gd, Si and Ge as standards for the EDS and WDS measurements. Magnetic measurements were done in a Quantum Design SQUID magnetometer. Phase compositions were first determined using EDS in a Leo SEM, and then using WDS in a Jeol JXA 8900 RL EPMA. The WDS measurements of global compositions were done with a 100 mm electron spot probe. 3. Results and discussions The as-cast samples presented only one magnetic second-order transition at 299 K: After the heat treat- ment at 1600  C=48 h; the samples show two transitions, one at 299 K; and a second one at 269 K on heating and ARTICLE IN PRESS *Corresponding author. Tel.: +55-19-3788-5385; fax: +55- 19-3788-5376. E-mail address: gama@ifi.unicamp.br (S. Gama). 0304-8853/$-see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1260