New Type Metamagnetism in Co(S_<i>x</i>Se_1-<i>x</i>)₂: Exchange-Compensated Paramagnetism

Abstract

The magnetic phase diagram of Co(S x Se 1- x ) 2 , the solid solution between ferromagnetic CoS 2 and antiferromagnetic CoSe 2 , has been given by neutron diffraction experiment, where the paramagnetism at absolute zero was found in the range 0.5< x <0.88. This paramagnetic state is named “exchange-compensated paramagnetism”. A new type metamagnetism has been found in this paramagnetic state at x =0.86. This behavior had been already predicted theoretically by M. Hattori, K. Adachi and H. Nakano in J. Phys. Soc. Japan 26 (1969) 642. The metamagnetic properties have been measured under a strong magnetic field up to 75 kOe and in the temperature range 4.2°K to 800°K. The metamagnetism shows the hysteresis without remanence below 34°K and the saturation moment agrees with that of CoS 2 . The obtained results have been analyzed from the thermostatistical standpoint with an analogy of the condensation of imperfect gas and the critical indices have been determined. The origin of the exchange-compensated paramagnetism and the mechanism of the metamagnetism have been discussed.