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

Abstract

The crystal structure of new Mo2NiB2-type {Gd, Tb, Dy}2Ni2.35Si0.65 (Immm, No. 71, oI10) and La2Ni3-type {Dy, Ho}2Ni2.5Si0.5 (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 ~66K, whereas isostructural Tb2Ni2.35Si0.65 shows an antiferromagnetic transition at ~52K 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)μB at 2K.The La2Ni3-type Dy2Ni2.5Si0.5 exhibits ferromagnetic like transition at ~42K with coexisting antiferromagnetic interactions and field induced metamagnetic transition below ~17K.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 −14.3J/kgK, −5.3J/kgK and −10.3J/kgK for a field change of 50kOe near 66K, 52K and 42K, 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 +12.8J/kgK and ~+9.9J/kgK, respectively at 7K for a field change of 50kOe.