Magnetic ordering of YPd2Si-type HoNi2Si and ErNi2Si compounds

Abstract Magnetic properties of YPd2Si-type HoNi2Si and ErNi2Si were investigated via neutron diffraction and magnetisation measurements. HoNi2Si and ErNi2Si show ferromagnetic-like ordering at TC of 9 K and 7 K, respectively. The paramagnetic Weiss temperatures are 9 K and 11 K and the effective magnetic moments are 10.76 μB/fu and 9.79 μB/fu for HoNi2Si and ErNi2Si compounds, respectively. The HoNi2Si and ErNi2Si are soft ferromagnets with saturation magnetization of 8.1 μB/fu and 7.5 μB/fu, respectively at 2 K and in field of 140 kOe. The isothermal magnetic entropy change, ΔSm, has a maximum value of −15.6 J/kg·K at 10 K for HoNi2Si and −13.9 J/kg·K at 6 K for ErNi2Si for a field change of 50 kOe. Neutron diffraction study in zero applied field shows mixed ferromagnetic-antiferromagnetic ordering of HoNi2Si at ~9 K and its magnetic structure is a sum of a-axis ferromagnetic Fa, b-axis antiferromagnetic AFb and c-axis antiferrromagnetic AFc components of Pn′a21′={1, mx′/[1/2, 1/2, 1/2], 2y′/[0, 1/2, 0], mz/[1/2, 0, 1/2]} magnetic space group and propagation vector K0=[0, 0, 0]. The holmium magnetic moment reaches a value of 9.23(9) μB at 1.5 K and the unit cell of HoNi2Si undergoes isotropic contraction around the temperature of magnetic transition.