Theory of Antiferromagnetic Resonance

Abstract

The spin resonance condition $\frac{\ensuremath{\omega}}{\ensuremath{\gamma}}={H}_{0}\ifmmode\pm\else\textpm\fi{}{[{H}_{A}(2{H}_{E}+{H}_{A})]}^{\frac{1}{2}}$ previously given by Kittel for a disk-shaped single-domain uniaxial or cubic antiferromagnetic crystal at 0\ifmmode^\circ\else\textdegree\fi{}K with ${H}_{0}$ parallel to the domain axis is extended by classical calculations to cover finite temperature, ellipsoidal shape, orthorhombic symmetry, generalized two-lattice anisotropy, and arbitrary static field direction. The normal precessional modes are discussed. A quantum-mechanical derivation of the resonance equations is carried out by the method developed by Van Vleck for ferromagnetic resonance; no new features are introduced by the quantum-mechanical calculation. Several factors contributing to the line width are considered. Existing experimental data on antiferromagnetic resonance are reviewed; the data are scanty and taken in circumstances not closely related to the situation envisaged by the theory.