Specific Heat Study of Magnetic Ordering and Band Structure of 3d Transition Metal Disulfides Having the Pyrite Structure

Specific heats of FeS 2 -CoS 2 -NiS 2 Solid solutions and of Ni 0.95 Cu 0.05 S 2 have been measured from 10 K to 350 K. Debye temperatures, coefficients of electronic contribution γ, magnetic ordering temperatures, and magnetic entropies have been determined. The magnetic entropy of ferromagnetic Fe 1- x Co x S 2 is proportional to cobalt concentration and is 40% of that expected for a localized spin 1/2 per Co atom, suggesting an itinerant character of e g electrons. The magnetic entropy of NiS 2 is smaller than that of a localized spin 1 and is in good agreement with that expected for the magnetic moment observed by neutron diffraction. The magnetic entropy of antiferromagnetic Co 1- x Ni x S 2 Suggests that only Ni atoms have magnetic moment in Ni-rich phase. The density-of-states curve of e g band for NiS 2 has been constructed from γ values assuming a rigid band. The band width of lower half of e g band is 0.6 eV. The Debye temperature decreases monotonously from 605 K of FeS 2 to 455 K of NiS 2 .