FERROMAGNETISM AND ANTIFERROMAGNETISM IN AN ORGANIC RADICAL CRYSTAL

Recently, the transition to ferromagnetic order has been found in crystals of genuine organic compounds consisting only of light elements such as carbon, nitrogen and oxygen. The first example of an organic ferromagnet was the orthorhombic beta-phase crystal of p-nitrophenyl nitronyl nitroxide (C13H16N4O3) Its ferromagnetism (T-c = 0.6 K) has been established by various experiments such as susceptibility, magnetization, heat capacity, zero-held muon spin rotation and ferromagnetic resonance. Details of these measurements are reviewed in this article. On the other hand, the triclinic gamma-phase crystal of this compound becomes an antiferromagnet at T-N = 0.65 K. Its magnetic properties are also described briefly.