Magnetic Phase Transition of Organic Free Radical p-Cl-BDPA

Abstract

The heat capacity of polycrystalline organic free radical, p -Cl-BDPA, has been measured between 1.5 and 20 K. The broad maximum near 5 K in the magnetic heat capacity corresponds the short range magnetic ordering of the unpaired electron. At 3.25 K a sharp peak was observed, which indicates paramagnetic-antiferromagnetic phase transition. The magnetic entropy of this transition yields 101.5% of the expected Rln2. Below T N the magnetic heat capacity was in good agreement with the three-dimensional spin wave theory of antiferromagnet.