Search

In this paper, calculation has been carried out for the localized modes of spin waves around a magnetic impurity atom in a ferromagnetic of the simple cubic structure. There are three symmetry types, i.e., the s-type, the p-type and the dr-type mode. The wave functions and the curves of the energy levels against the parameter J'S'/JS of these modes are obtained. Next, the types of localized modes which may possibly exist in ferromagnetics of the bcc or the fcc structure are discussed. It is pointed out that probably the s-type mode is the only one to be expected in actual specimens. With the criterion that the Curie point of the specimen should increase with the concentration of impurity, several alloys are suggested for the experimental observation of the localized modes of spin waves. Finally, a general analysis of the spin quantum number of the spin wave states leads to the conclusion that it is impossible to excite the scattered modes with k0≠0 as well as the localized modes by the electromagnetic radiation.

In ferromagnets and antiferromagnets, the coupling between phonons and magnons cannot be overlooked, because of the exchange interaction changing with the distance between the magnetic ions. In this article, the possible effect of this coupling on the infrared absorption in magnetic insulators has been considered. The transition involved consists of the excitation of an optical phonon by the interaction with radiation field and simultaneously that of two magnons and a phonon due to the perturbation of the phonon-magnon coupling. It produces an absorption band with frequencies higher than the edge of the lattice absorption. Since the total spin component S z must be conserved, this effect should not be found in ferromagnetic insulators. If the Neel temperature of an antiferromagnet is high enough and the distribution of spin wave states vs. energy has a sharp maximum the predicted absorption band becomes observable. Our treatment is aimed at the 0.24 eV absorption band of NiO. Its peak energy and absorption constant are calculated. The results appear in fair agreement with the experimental findings. Finally, it is pointed out that the transition process adopted by Mizuno and Koide for explaining the same phenomenon can only offer a secondly effect in comparison with ours.