Mo2NiB2-type {Gd, Tb, Dy)2Ni2.35Si0.65 and La2Ni3-type {Dy, Ho}2Ni2.5Si0.5 compounds: Crystal structure and magnetic properties

The crystal structure of new Mo2NiB2-type {Gd, Tb, Dy}(2)Ni2.35Si0.65 (Immm, No. 71, oI10) and La2Ni3-type {DY, Ho}(2)Ni2.5Si0.5 (Cmce No. 64, oC20) compounds has been established using powder X-ray diffraction studies. Magnetization measurements show that the Mo2NiB2-tYpe Gd2Ni2.35Si0.65 undergoes a ferromagnetic transition at similar to 66 K, whereas isostructural Tb2Ni2.35Si0.65 shows an antiferromagnetic transition at similar to 52 K and a field-induced metamagnetic transition at low temperatures. Neutron diffraction study shows that, in zero applied field, Tb2Ni2.35Si0.65 exhibits c-axis antiferromagnetic order with propagation vector K={1/2, 0, 1/2] below its magnetic ordering temperature and Tb magnetic moment reaches a value of 8.32(5) mu(B) at 2K. The La2Ni3-type Dy2Ni2.5Si0.5 exhibits ferromagnetic like transition at similar to 42 K with coexisting antiferromagnetic interactions and field induced metamagnetic transition below similar to 17 K. The magnetocaloric effect of Gd2Ni2.35Si0.65, Tb2Ni2.35Si0.65 and Dy2Ni2.5Si0.5 is calculated in terms of isothermal magnetic entropy change and it reaches a maximum value of -14.3 J/kg K. -5.3 J/kg K and -10.3 J/kg K for a field change of 50 kOe near 66 K, 52 K and 42 K, respectively. Low temperature magnetic ordering with enhanced anisotropic effects in Tb2Ni2.35Si0.65 and Dy2Ni2.35Si0.65 is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +12.8 J/kg K and similar to+9.9 J/kg K. respectively at 7 K for a field change of 50 kOe. (C) 2015 Elsevier Inc. All rights reserved.