Magnetic properties of the itinerant metamagnetic systemCo(S1−xSex)2under high magnetic fields and high pressure

Abstract

The magnetization of the $\mathrm{Co}({\mathrm{S}}_{1-x}{\mathrm{Se}}_x{)}_2$ system with $0<~x<~0.2$ has been measured under high magnetic fields and high pressure. Ferromagnetic ${\mathrm{CoS}}_2$ exhibits a second-order transition at $T_c=122\mathrm{}\mathrm{K}.$ Substitution of 10% Se for S in ${\mathrm{CoS}}_2$ reduces the Curie temperature to $T_c=27\mathrm{}\mathrm{K}$ and the transition to first order. $\mathrm{Co}({\mathrm{S}}_{1-x}{\mathrm{Se}}_x{)}_2$ with $0.12<~x$ becomes an exchange-enhanced Pauli paramagnet. The itinerant metamagnetic transition has been observed in the paramagnet. ${\mathrm{C}\mathrm{o}(\mathrm{S}}_{0.9}{\mathrm{Se}}_{0.1}{)}_2$ also shows a transition just above $T_c.$ Using the experimental data, the magnetic phase diagram of $\mathrm{Co}({\mathrm{S}}_{1-x}{\mathrm{Se}}_x{)}_2$ is determined. With increasing pressure, the Curie temperature of ${\mathrm{CoS}}_2$ decreases and the ferromagnetic transition changes to first order at $P\approx 0.4\mathrm{GPa}.$ In the pressure regime of the first-order transition $P>\mathrm{}0.4\mathrm{}\mathrm{GPa},$ the metamagnetic transition is observed just above $T_c.$ In ${\mathrm{C}\mathrm{o}(\mathrm{S}}_{0.9}{\mathrm{Se}}_{0.1}{)}_2,$ the ferromagnetism disappears at 0.25 GPa and paramagnetism appears. The observed magnetic properties and the magnetic phase diagram of $\mathrm{Co}({\mathrm{S}}_{1-x}{\mathrm{Se}}_x{)}_2$ can be qualitatively described with a theory of the itinerant electron metamagnetism at finite temperatures.