Magnetic properties of the itinerant metamagnetic system Co(S1-xSex)(2) under high magnetic fields and high pressure

The magnetization of the Co(S1-xSex)(2) system with 0 less than or equal to x less than or equal to 0.2 has been measured under high magnetic fields and high pressure. Ferromagnetic CoS2 exhibits a second-order transition at T-c = 122 K. Substitution of 10% Se for S in CoS2 reduces the Curie temperature to T-c = 27 K and the transition to first order. Co(S1-xSex)(2) with 0.12 less than or equal to x becomes an exchange-enhanced Pauli paramagnet. The itinerant metamagnetic transition has been observed in the paramagnet. Co(S0.9Se0.1)(2) also shows a transition just above T-c. Using the experimental data, the magnetic phase diagram of Co(S1-xSex)(2) is determined. With increasing pressure, the Curie temperature of CoS2 decreases and the ferromagnetic transition changes to first order at P approximate to 0.4 GPa. In the pressure regime of the first-order transition P > 0.4 GPa, the metamagnetic transition is observed just above T-c. In Co(S0.9Se0.1)(2), the ferromagnetism disappears at 0.25 GPa and paramagnetism appears. The observed magnetic properties and the magnetic phase diagram of Co(S1-xSex)(2) can be qualitatively described with a theory of the itinerant electron metamagnetism at finite temperatures.