Thermodynamic Properties of
Magnetic Phase Transition in Magnetic Organic Superconductor κ-(BETS)2FeCl4

Magnetic superconductor κ-(BETS)2FeCl4 consisting of organic donor molecules and inorganic anions with 3d spins has attracted much attention since it exhibits novel magnetic and conducting properties such as coexistence state of magnetic ordering and superconductivity and magnetic field induced superconductivity. In this study, we performed heat capacity measurements for κ-(BETS)2FeCl4 and mainly investigated the thermal properties of magnetic phase transition. We observed a large symmetric thermal anomaly at 0.47 K which is originated from localized d electrons. This anomaly is suppressed easily when magnetic field was applied parallel to the a-axis but is not suppressed so much when magnetic field was applied parallel to c-axis. These results indicate that the magnetic ordered state has two dimensional character and strong magnetic anisotropy.

(by S. Fukuoka & Y. Nakazawa)

Fig. 1. Cp vs T curve of κ-(BETS)2FeCl4. The large thermal anomaly corresponds to magnetic phase transition originated from localized 3d electrons.

Fig. 2. Temperature dependence of magnetic entropy of κ-(BETS)2FeCl4.

Fig. 3. Cp vs T curves of κ-(BETS)2FeCl4 under magnetic field. Magnetic fields are applied parallel to a-axis and c-axis.