Low Temperature Heat Capacity Measurements of an Organic Conductor Based on BETS Molecule

κ–(BETS)2FeBr4 is the first organic conductor in which superconductivity coexists with antiferromagnetic ordering.We have performed a heat capacity measurement under 4 K in order to study magnetic properties of anion layers by the ac technique. A distinct thermal anomaly corresponding to an antiferromagnetic transition was observed at 2.2 K under 0 T. The peak temperature has been shifted to the lower temperature by applying magnetic fields. The tendency is the largest when the magnetic field was applied parallel to the a-axis.

(by S. Fukuoka & T. Yamamoto)

	Fig. 1. Molecular structures of BETS and FeBr4-
	Fig. 2. Temperature dependence of heat capacity of κ-(BETS)2FeBr4 under magnetic fields. Magnetic fields are applied in three directions. The suppression of TN is the largest when magnetic field is applied parallel to the a axis.
	Fig.3. Magnetic fields dependence of the heat capacity of κ-(BETS)2FeBr4. Magnetic fields are applied to the intermediate direction between the a and c axes. The antiferromagnetic transition temperature is shifted to lower temperature side with the increase of magnetic field.