Magnetic phase diagram of the organic antiferromagnet F4BImNN

Abstract We present a combination of heat capacity and ac susceptibility measurements as a function of temperature and field, of a single crystal of the radical 2-(4,5,6,7-tetrafluorobenzimidazol-2-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl. Our results confirm a zero-field Neel temperature at T N (0) = 0.73 K and allow the determination of the critical field parameters H c (||) = 170 Oe and H c (⊥) = 306 Oe. Assuming the previously determined 1-D intrachain ferromagnetic exchange interaction of J intra /k  = +22 K between radicals, the interchain antiferromagnetic interaction is calculated as z J inter /k  ∼ −0.03 K.