New ternary Yb5Sb3-type R5T1-x{Sb, Bi}2+x phases (R = Y, Dy, Ho, T = Co, Ru, Rh, Pd) and their magnetic properties

Several novel R5T1-x{Sb,Bi}(2+x) phases having the Yb5Sb3-type structure (space group Pnma) have been synthesized. The cell parameters are: a = 1.20668(9), b = 0.88396(7), c = 0.78745(7) nm for Y5CoSb2; a = 1.19939(7), b = 0.88364(5), c = 0.78283(5) nm for Dy5CoSb2; a = 1.19633(8), b = 0.89231(6), c = 0.78450(6) nm for Ho5RhSb2; a = 1.18650(6), b = 0.90455(4), c = 0.79260(4) nm for Ho5PdSb2; a = 1.2215(3), b = 0.8948(2), c = 0.7977(2) nm for Y5CoBi2; a = 1.1781(8), b = 0.9071(7), c = 0.7936(6) nm for Tm5Co0.5Bi2.5; a = 1.1972(1), b = 0.92096(9), c = 0.80048(9) nm for Ho5RuBi2; a = 1.2082(1), b = 0.90346(9), c = 0.79413(8) nm for Ho5RhBi2 and a = 1.20374(5), b = 0.91076(4), c = 0.80135(4) nm for Ho5PdBi2, respectively. Magnetization measurements indicate ferromagnetic transitions for Dy5CoBi2, Ho5RhSb2, Ho5RhBi2, Ho5PdSb2 and Ho5PdBi2 at T-C = 34, 38, 28, 42 and 38 K. respectively. The Ho5RhSb2 and Ho5PdBi2 compounds show additional magnetic transitions at about 18 K, probably associated with a spin reorientation. The magnetocaloric effect of Dy5CoBi2 in terms of the isothermal entropy change, Delta 5(m), is -6.2 J/(kg/K) at 38 K and in terms of the adiabatic temperature change. Delta T-ad, is 2.2 K for a 5 T field change. (C) 2010 Elsevier Ltd. All rights reserved.