Electrical Resistivity and Thermal Expansion Anomalies of Ferromagnetic CoS₂

The resistivity of CoS 2 having the pyrite structure was measured between 4.2 K and 300 K under pressure up to 18 kbar and under magnetic field up to 45 kOe. The hump anomaly just below the Curie temperature ( T c ) was found to become sharper with decreasing T c by pressure and to become sluggish with increasing T c by field. The magnetization ( M ) dependence of both the hump anomaly below T c and a positive magnetoresistance above T c was empirically analyzed, which resulted in M 2 dependent effective mass. The spontaneous and induced volume-strictions were also measured near T c up to 45 kOe, the latter of which was found to vary as M 2 for small M . These anomalies can be qualitatively understood through the variations of M and T c in a unified way including the effect of impurity-doping.