MAGNETIC-FIELD VERSUS TEMPERATURE PHASE-DIAGRAM OF A QUASI-ONE-DIMENSIONAL S=1 HEISENBERG-ANTIFERROMAGNET

From a heat capacity (C-p) measurement on a single crystal sample of t he S = 1 quasi-one-dimensional(Q1D) Heisenbeg antiferromagnet (HAF) Ni (C5H14N2)(2)N-3(PF6) in applied magnetic fields, we found an anomaly w hich is indicative of a magnetic long-range ordering. We were able to follow how the position of the anomaly in C-p changes with temperature (T) and magnetic field (H). An experimental H-T phase diagram of an S = 1 Q1D HAF is obtained and compared with that of the corresponding c lassical system. [S0031-9007(98)07105-1].