Mössbauer study ofNi0.01Fe0.99S

The effects of nickel ions on crystallographic and spin-flip transitions in FeS have been studied using the Mössbauer effect. It is found that only 1% impurity of ${\mathrm{Ni}}^{2+}$ in FeS causes hysteresis of such large temperature widths as 13 K in the crystallographic α transition and 20 K in the spin-flip transition, whereas no appreciable hysteresis is found in $M_{0.025}$ ${\mathrm{Fe}}_{0.975}$S (M=Sc, Ti, Cr, Mn, Co, Cu). The above Ni impurity also causes a hysteresis in the temperature of coexistence of two crystallographic phases.