The S = 1 quasi-one-dimensional Heisenberg antiferromagnet [Ni(C5H14N2)2N3](PF6), abbreviated as NDMAP, has been studied by electron spin resonance in a magnetic field above the critical field (Hc). We studied angular and frequency dependences of spin excitations. The angular dependence of the spin excitations in the vicinity of Hc is explained well by a phenomenological field theory, but the agreement between the experiment and the calculation is not satisfactory above 10 T. In high magnetic fields above 15 T, we obtained some characteristic spin excitations which are well explained by conventional antiferromagnetic resonance modes. These results suggest that the spin excitations change from a quantum state to a classical one due to the suppression of quantum fluctuations by high magnetic fields.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics