Magnetic Properties of Cobalt and Nickel Dichalcogenide Compounds with Pyrite Structure

Abstract

The magnetic properties of dichalcogenide compounds, CoS₂, CoSe₂, NiS₂, NiSe₂ and the system Co(S_xSe_1−x)₂, were studied by means of magnetic measurement, neutron diffraction and NMR. The exchange interaction J_sw of the ferromagnetic CoS₂ (T_c=124°K, θ_p=220°K, p_eff=1.76_μB, n=0.84_μB and H_i=52 kOe) was estimated to be 24 cm⁻¹ per Copair from the analysis of spin wave theory. While, CoSe₂ (T_N=90°K, θ_p=−160°K and p_eff=1.72_μB) showed an antiferromagnetic spin ordering with MnSe₂ type. NiS₂ (θ_p=−740°K and p_eff=2.48_μB) had no magnetic ordering even at 4.2°K. NiSe₂ exhibited weak constant paramagnetism with metallic conductivity. In Co(S_xSe_1−x)₂, (0≤x≤1), the magnetic properties and the magnetic phase diagram were determined, and this system showed to have “low spin state” with 1_μB per Co. Some discussions were given from the theoretical stand points.