Novel Spin Excitations in the Field-Induced Phase of the Haldane Magnet Ni(C_5H_<14>N_2)_2N_3(PF_6)(Condensed matter : electronic structure and electrical, magnetic, and optical properties)

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We have performed electron spin resonance measurements on single crystals of the S=1 one-dimensional Heisenberg antiferromagnet Ni(C_5H_<14>N_2)_2N_3(PF_6) in magnetic fields up to about 55 T and at frequencies up to about 2 THz. For both H ‖ chain and H ⊥ chain, we have found that one of the two or three excitation modes that are observed in magnetic fields between the critical field (H_c) and about 15 T survives in the high-field region. This mode approaches a paramangetic resonance line at high-fields and fits well with the conventional antiferromagnetic resonance mode with easy-plane anisotropy. This result suggests that the spin-excitation modes above H_c change from modes affected by quantum fluctuations to those expected for a conventional antiferromagnet.
社団法人日本物理学会の論文
2007-10-15