Heat Capacity and Magnetic Phase Transition of the Molecule-Based Magnet
DOT• + · GaIII Cl4−

Heat capacities of 2,2′:6′,2″-dioxytriphenylamine radical cation DOT• + (S = 1/2) and non-magnetic GaIII Cl4− salt DOT• + · GaIII Cl4− were measured by relaxation method under magnetic fields. A heat capacity peak was observed at 2.97 K. This peak is due to antiferromagnetic phase transition from the magnetic field dependence of the peak temperature. The estimated magnetic entropy 5.80 J K−1 mol−1 is close to Rln2 (= 5.76 J K−1 mol−1) for S = 1/2 spin systems. The zero-field magnetic heat capacity above the magnetic phase transition temperature is expressed well by the theoretical heat capacity curve for the high-temperature expansion of an S = 1/2 one-dimensional antiferromagnetic Heisenberg model with the intrachain magnetic interaction J/kB = −4.1 K. From the mean-field approximation by use of the derived intrachain magnetic interaction and the magnetic phase transition temperature, the interchain magnetic interaction was estimated to be |zJ′/kB| ≈ 8.7 K.

(by X.-Z. Lan & Y. Miyazaki)

	Fig. 1. Molecular structure of DOT• +.
	Fig. 2. Heat capacities of DOT• + · Ga Cl4− under magnetic fields. Solid curve indicates the lattice heat capacity. For the sake of clarity, the heat capacities except for the zero-field heat capacity are shifted upwards.
	Fig. 3. Magnetic heat capacities of DOT• + · Ga Cl4− under magnetic fields. For the sake of clarity, the magnetic heat capacities except for the zero-field magnetic heat capacity are shifted upwards. Solid curve indicates the theoretical heat capacity for high-temperature expansion of S = 1/2 one-dimensional antiferromagnetic Heisenberg model with J/kB = −4.1 K.