THERMOSTATISTICAL INVESTIGATION OF MAGNETIC AND THERMAL PROPERTIES OF COBALT DICHALCOGENIDE COMPOUND CO(SXSE1-X)2 WITH PYRITE STRUCTURE

A statistical-mechanical calculation on the system of spins of quantum number one half which constitute a face-centred cubic lattice and couple not only with the nearest-neighbour spins but also with the second-neighbour spins due to the exchange interactions is carried out with the use of the inverse temperature expansion. By the application of this calculation, the magnetic and thermal properties of cobalt dichalcogenide compound Co(SxSe1-x)2of various values of the fraction x with pyrite structure is discussed, assuming that the antiferromagnetic exchange coupling between a pair of second-neighbour spins gets stronger with decreasing of the fraction x. The correspondence between the theory and experiment is quite well in all respects. The appearance of a certain metamagnetic transition is predicted in the compound of an intermediate x value which is not ferromagnetic although no ample measurement of the magnetization in variable magnetic field at various temperatures has been carried out yet enough to examine the existence of this kind of transition. The heat capacity is also discussed. © 1969, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.