Antiferromagnetic Resonance in Systems with Dzyaloshinsky-Moriya Coupling; Orientation Dependence inαFe2O3

Resonance conditions for an antiferromagnet whose sublattice magnetization vectors are canted by the Dzyaloshinsky-Moriya interaction are generalized to include an arbitrary angle $\theta$ between the applied magnetic field and the hard direction of magnetization, and the resulting normal modes are discussed. A correction term to the low-frequency resonance expressions derived by Pincus may be appreciable at higher magnetic fields and small $\theta$. For suitable parameters, this term permits the measurement of all pertinent effective fields by resonance experiments. It is furthermore shown that demagnetization effects are negligible. Microwave resonance experiments as a function of field (to 60 kG), angle, and frequency (12 to 35 Gc/sec) on synthetic single crystals of $\alpha {\mathrm{Fe}}_2{\mathrm{O}}_3$ failed to reveal a departure from the Pincus relation, thus leading to the conclusion that $\frac{H_A}{H_E}<{10}^{-2\mathrm{}}$.