Magnetic Phase Transitions
of Chiral Magnets under Magnetic Fields

Chiral magnets are expected to form unique magnetic structures due to their chiral crystal structures. In this work, we have performed heat capacity measurements for chiral magnets, [W(CN)8]4[Cu(pn)H2O]4[Cu(pn)]2•2.5H2O (S- and rac-pn =1,2-diaminopropane) around the anti-ferromagnetic phase transition by thermal relaxation method. We observed a first-order anomaly just below TN for the S-compound, when magnetic fields are applied parallel to the b-axis. For the racemic compound, we could not observe such behavior. The heat capacity peak is soon suppressed in the racemic conpound. These results mean that this anomaly is one of novel phenomena of the chiral structure of magnetic moments.

(by S. Fukuoka & T. Yamamoto)

	Fig. 1. Heat capacities of chiral magnets around antiferromagnetic phase transition. As for the S-compound, a shoulder is observed just below TN.
	Fig.2. Magnetic field dependence of heat capacities of the S-compound. The shoulder grows to a first-order anomaly under the magnetic field of 1 T.
	Fig.3. Temperature dependence of heat capacities under 1 T of the S-compound. The first-order transition disappears when the field direction has been changed to the perpendicular direction for the b-axis.