MAGNETIC-PROPERTIES OF THE COS2-XSEX COMPOUNDS .2. NEUTRON-DIFFRACTION AND NMR INVESTIGATION OF THE MAGNETISM AND THE METAMAGNETIC TRANSITION

For pt.I see ibid., vol.12, p.4269 (1979). From neutron diffraction and NMR experiments it is shown that the magnetism of chemically homogeneous CoS 2-xSex compounds is characterised by inhomogeneously distributed moments on the Co atoms. Some of the cobalt atoms carry the same moment, 0.9 mu B, as in pure CoS2 whereas others are non-magnetic. The concentration and field dependence of the magnetisation are almost entirely due to the corresponding variation in the number of magnetic atoms, while the moment carried by these atoms remains nearly constant. The temperature dependence of the magnetisation is also attributable, for the main part, to the same mechanism, whereas thermal variation of the moment carried by these atoms remains nearly constant. The temperature dependence of the magnetisation is also attributable, for the main part, to the same mechanism, whereas thermal variation of the moment is only responsible for a small part of the loss of magnetisation when T increases. Furthermore, the thermal variation is almost concentration-independent. It is suggested that the cobalt atoms in CoS2-xSex compounds have two magnetic states depending on the local environment, temperature and magnetic field: a non-magnetic and a magnetic state, which always has the same moment, 0.9 mu B. In this type of material field-induced transition results from cobalt atoms switching from the non-magnetic to the magnetic state; cooperative phenomena acting through the coupling between cobalt atoms can then explain the hysteresis observed for this transition.