Magnetic Study of NiS₂ Single Crystals

Abstract

Magnetic measurements were made, in the weak ferromagnetic temperature region (≤30 K) and in fields to 55 kOe, on two single crystal samples without and with Co impurities, respectively. The magnetization along α direction is well expressed by M(α)=M₀(α)+χ_w(α)H at higher fields to 55 kOe without any anomaly like a spin flip. The ratio of M₀[001] : M₀[110] : M₀[111] is equal to almost 1 : 1⁄\sqrt2 : 1⁄\sqrt3. χ_w(α) was found to be almost temperature independent, and to be weakly anisotropic. The transition at T_c is of the first order and T_c increased in magnetic fields (dT_c⁄dH=+(2.7±0.5)×10⁻³ K/kOe). The entropy change was estimated as 0.7±0.2 (J/K·mol). Co impurities were found to strongly affect some of magnetic properties. Discussions are given on origins of weak ferromagnetism together with other properties. The origin proposed by Yoshimori et al. seems to work in NiS₂.