DEMAGNETIZING EFFECTS ON ANTI-FERROMAGNETIC RESONANCE IN CSNIF3

Antiferromagnetic resonance in CsNiF3 has been investigated at 35, 24 and 9 GHz bands between r=1.3 K and the Néel temperature (TN=2.61 K). The resonance frequencies are seriously dependent on sample shape. The results can be understood by a molecular field theory including both the surface demagnetization and the Lorentz fields. The critical field of the phase transition from the spin-flop to the paramagnetic phase has been obtained. The data at T= 1.4 K allow a determination of the parameters: antiferromagnetic interchain exchange field HE=990±50 Oe, in-plane anisotropy field HA1 =210±20 Oe and sublattice magnetization M=96±5 emu/cm3. The in-plane anisotropy due to the dipolar interaction is estimated to be 245 Oe in reasonable agreement with the observation. From the zero-field gap frequency a large negative anisotropy along the c-axis is dtermined to be HA2=60±3 kOe or D/k=9.2±0.5 K. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.