The S=1 quasi-one dimensional Heisenberg antiferromagnet Ni(C 5H14N2)2N3(PF6), abbreviated as NDMAP, has been studied by electron spin resonance (ESR) in a magnetic field exceeding the critical field (Hc) above which this compound shows a long range order (LRO) at sufficiently low temperatures. Our recently developed ESR apparatus with a dilution refrigerator is utilized to study the spin excitations of NDMAP above Hc for Hc, because this compound exhibits the LRO below about 1 K. The spin excitation modes above Hc observed below 1 K do not show any difference from those at 1.5 K and the lowest excitation mode observed at 30 mK in the inelastic neutron experiments above Hc was not observed at about 200 mK in this study. Accordingly, the result suggests that the lowest excitation mode is very sensitive to temperature.
ASJC Scopus subject areas
- Physics and Astronomy(all)