From microwave cavity transmission measurements at 23-110 GHz on λ-(BEDT-TSF)2FeCl4, we have observed an antiferromagnetic resonance (AFMR) in the antiferromagnetic insulating state below the metalto-insulator transition temperature of TMI=8.3 K. The frequency-field dependence is fundamentally reproduced with a two-sublattice model for a biaxial anisotropy. The easy axis is confirmed to be the direction tilted by 30° from c to b*, and the hard axis is found to be close to a*. The spin-flop field is identified to be 1.3 T through the frequency-field dependence for the easy axis. The AFMR is interpreted to be caused by spin waves excited on the π spins, exclusively due to the large π-π exchange interaction estimated by theoretical calculations. The exchange field and anisotropy fields for π spin systems at 1.2 K are evaluated to be HE ∼330 T, HA1∼ 1.5×10-3 T for the intermediate axis and HA2∼5.0×10-3 T for the hard axis, respectively.
|ジャーナル||Physical Review B - Condensed Matter and Materials Physics|
|出版ステータス||Published - 2003 1月 1|
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