On the Ferrimagnetism of Iron Selenides

The thermomagnetic properties of iron selenides FeSe x with various selenium contents x were measured as functions of temperature. The thermomagnetic curves obtained belong to the ordinary Weiss type. It was also found that the magnetization at the boiling temperature of liquid nitrogen increases with the selenium content, reaches its maximum value. 35 gauss, at x =1.23, and then decreases again with further increase of x . The Néel temperature was approximately 150°C in the range of x from 1 to 1.26 whereas it decreases gradually with further increase of x and approaches to its lowest value 30°C at x =1.35. The origin of the magnetization of this substance was discussed based on the theory of ferrimagnetism.