Magnetization distribution in COS2;: is it a half metallic ferromagnet?

Polarized neutron diffraction has been used to determine the spatial distribution of the magnetization in CoS2 and its temperature dependence. Although the previously reported ground state moment 0.84 mu(B) is non-integral, the compound has sometimes been classified as a half metallic ferromagnet. The present results show that the ferromagnetic phase cannot have half metallic properties. The magnetization distribution around the Co2+ ions in the ferromagnetic phase at 1.8 K is nearly spherical, indicating that, contrary to electronic structure calculations, electrons both of e(g) and t(2g) character contribute to the observed magnetic moment. The orbital contribution to the moment is found to be small, a factor of two less than that determined from magnetic circular dichroism measurements. A small moment, approximately 2% of that on the cobalt ions, resides on the sulfur atoms at 1.8 K. The magnetization distribution induced in the paramagnetic phase by a field of 9.6 T at 150 K is significantly different from that in the ferromagnetic state and has the asphericity characteristic of e(g) electrons. On heating to 300 K and then to 400 K the t(2g) character of the magnetization increases continuously and becomes predominant above the anomaly in the susceptibility at 350 K.