Magnetoelasticity of CoS2

The magnetization of an itinerant ferromagnet CoS2 has been measured in hig h magnetic fields under high pressures. The Curie temperature, T-C = 121 K at ambient pressure decreases with increasing pressure with the rate dT(C)/ dP = -5.1 K GPa(-1) The second-order type ferromagnetic transition at T-C c hanges into the first-order type for P greater than or equal to 0.4 GPa, wh ere a metamagnetic transition in magnetic field was observed just above T-C . From the analysis of the magnetization curve for 1.3 GPa, the Landau expa nsion coefficients of the magnetic free energy were determined. We found th at the second- and fourth-order coefficients tend to change the sign around T-C. From the thermal expansion measurements, the magnetovolume coupling c onstant is determined as n(dd) = (1-2) x 10(-3)mu(B)(-2) This value is cons istent with that estimated from the pressure effect on the magnetization at low temperatures.