Structure, magnetic and magnetocaloric properties of RE 11 Ge 8 In 2 (RE ¼ GdeTm) Yan Yin Janice Cheung, Volodymyr Svitlyk, Yurij Mozharivskyj * Department of Chemistry and Chemical Biology, McMaster University, ABB 423, 1280 Main Street West, Hamilton, Ontario, L8S 4M1 Canada article info Article history: Received 23 August 2010 Received in revised form 28 September 2010 Accepted 6 October 2010 Available online 11 November 2010 Keywords: A. Rare-earth intermetallics B. Crystal chemistry of intermetallics B. Magnetic properties F. Diffraction abstract A new tetragonal Gd 11 Ge 8 In 2 phase has been obtained by arc-melting and annealing at 800  C. The structure has been determined and refined from single crystal X-ray diffraction data in the I4/mmm space group with a ¼ 11.2091(6) and c ¼ 16.3994(9) Å. Phases with the RE 11 Ge 8 In 2 (RE ¼ GdeTm) composition were subsequently synthesized and their structures were refined using X-ray powder diffraction methods. Magnetic measurements carried out on RE 11 Ge 8 In 2 (RE ¼ GdeTm) indicated a ferromagnetic ordering in all phases. The magnetocaloric effect in terms of the magnetic entropy change, DS mag , was evaluated for the Gd-, Tb- and Tm-containing samples, and the largest |DS mag | value of 10.6 J/kg K was obtained for Tm 11 Ge 8 In 2 . Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction As energy conservation becomes an important issue, scientists are exploring various ways to replace fossil fuels with clean, renewable energy sources and to increase energy efficiency. There are countless benefits for this approach, from environment to economic ones and to the overall quality of life. Refrigeration is one of the processes where the efficiency can be greatly improved. The efficiency of the conventional vapor-based refrigeration is only around 40% of the Carnot efficiency and it consumes 15% of the total energy generated worldwide [1]. In addition, it requires the usage of refrigerants that may contribute to the greenhouse effect. Alternatively, magnetic refrigeration, which is based on the magnetocaloric effect (MCE), is more efficient and also environmentally benign. This technique can have a wide range of applications, from sub-Kelvin cooling and gas liquefaction, to near-room temperature household and commercial refrigeration, freezing and air-conditioning. In the state-of-the-art magnetocaloric Gd 5 Si 2 Ge 2 material, a giant MCE results from coupling between the cleavage/reforma- tion of the interslab TeT dimers (here, T is a mixture of Si and Ge) and the magnetic phase transition [2]. The size effect and the valence electron count (VEC) have been found to be robust factors in determining the stability of the TeT dimers in the RE 5 T 4 phases (RE e rare-earth, T e p-element) [3e7]. In some of the studied systems, e.g. Gd 5 Si 4x Bi x [5] and Gd 5 Si 4x Sb x [6], the two effects were combined in a cooperative way to break the TeT dimers. By substituting indium into Gd 5 Ge 4 , the size and VEC effects are expected to oppose each other, which may result in interesting structural phenomena. Indium has three valence electrons, i.e. one less than germanium, so by decreasing the VEC, the interslab dimers in Gd 5 Ge 4x In x can be expected to reform. However, the atomic size of In is greater than that of Ge (r cov (In) ¼ 1.46 Å vs. r cov (Ge) ¼ 1.22 Å) [8], and thus In substitution will tend to stretch the interslab dimers. The atomic size has been shown to exert a smaller effect on the interslab TeT dimers in the RE 5 T 4 phases than the VEC. Therefore, one can expect to obtain structures with some or all of the interslab dimers reformed, provided the RE 5 T 4 - type structures form in the GdeGe-In system. Here we report structural studies of the Gd 5 Ge 4x In x samples and magnetic and magnetocaloric properties of the new RE 11 Ge 8 In 2 (RE ¼ GdeTm) phases. 2. Experimental 2.1. Synthesis and X-ray analysis The starting materials were pieces of GdeTm (99.9 wt.%, CERAC Inc.), Ge (99.9999 wt.%, Alfa Aesar) and In (99.99 wt.%, Alfa Aesar). Samples with the Gd 5 Ge 4x In x (0.25  x  2.5) compositions were arc-melted under Ar atmosphere four times to achieve homoge- neity. Cast samples were then sealed in evacuated silica tubes, annealed at 800  C for two weeks and quenched in cold water. Powder X-ray phase analysis was done on a PANalytical diffrac- tometer with the CoK a radiation to avoid fluorescence associated * Corresponding author. Tel.: þ1 905 525 9140x27796; fax: 1 905 521 2773. E-mail address: mozhar@mcmaster.ca (Y. Mozharivskyj). Contents lists available at ScienceDirect Intermetallics journal homepage: www.elsevier.com/locate/intermet 0966-9795/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2010.10.004 Intermetallics 19 (2011) 276e281