Thermodynamics of the ferromagnetic phase transition in nearly half metallic CoS2 at high pressures

•Specific volume of CoS2 at the ferromagnetic phase transition was measured by X-ray.•Heat capacity of CoS2 at the ferromagnetic phase transition was studied by AC method.•Volume change increases strongly along the transition line at high pressures.•Nearly half metallicity of CoS2 is confirmed by the heat capacity measurements.

The volume change and heat capacity at the ferromagnetic phase transition in CoS2 were measured at high pressures using X-rays generated by the Argonne synchrotron light source and by ac-calorimetry, respectively. The transition entropy, calculated on the basis of these experimental data, drops along the transition line due to quantum degradation, as required by Nernst's law. The volume change increases strongly along the transition line, which is explained by specifics of the compressibility difference of coexisting phases that results from nearly half metallic nature of the ferromagnetic phase of CoS2.