On the Metamagnetic Behavior of Fe0.864Se Single Crystals

Magnetization measurements on Fe 0.864 Se (3 c type) single crystals have been carried out around the temperature of spin axis transition ( T s =150 K). Above T s , the material behaves as a usual ferrimagnet having the easy plane (c plane). Below T s where the c axis is the easy direction, the observed magnetization curves have some resemblance to those of metamagnets: A sudden increase of magnetization occurs at a certain value of the applied field (10 3 ∼10 4 Oe) depending upon the field direction and the temperature. The hysteresis loop takes a constricted form with very small remanence (<5% of the saturation value). The composition range where these anomalies are observed is extremely narrow. The process of magnetization below T s is described as a field-induced first-order magnetic transition of the system of antiferromagnetically coupled regions. The origin of such regions is also discussed.