The spin resonance condition w/7 = i7o±[#A(2#j?+#A)]* previously given by Kittel for a disk-shaped single-domain uniaxial or cubic antiferromagnetic crystal at 0°K with Ho 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 quantummechanical 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.

No abstract

No abstract

No abstract

A study is made of the nature of the anisotropic superexchange interaction of the form D;ySiXS; recently proposed by Moriya. This interaction is permitted in jSMnS, with symmetry requiring that D»y be normal to the plane defined by i, j, and the single intervening anion. It is conjectured that this interaction leads to a screw spin arrangement, with a 90° screw angle; in crystals considered heretofore the Moriya energy produces only a slight canting. The observed powder neutron diffraction pattern has been interpreted as indicating ordering of the third kind with spins normal to the ordering axis; this arrangement, however, does not have minimum dipolar energy. The present proposed arrangement leads to the same diffraction pattern, and the Moriya energy probably overbalances the dipolar.