Magnetostatic Modes in Nanometer-sized Magnetic Wires, Anti-wires and Ringsn

Abstract

Motivated by recent experiments, a theoretical study of the magnetostatic modes in ferromagnetic and antiferromagnetic nanowires, anti-nanowires and nanor ings is presented. The external magnetic field is taken parallel to the cylindrical axis and the nanostructures have a large length-to-diameter aspect ratio. The surface and bulk magnetic excitations (or spin waves) are studied for cases where the dipole-dipole interactions are dominant in the spin dynamics. This situation can be realized at sufficiently small wavevectors by light scattering or magnetic resonance techniques. A macroscopic continuum theory is developed, us ing the magnetostatic form of Maxwell’s equations and electromagnetic boundary conditions. The characteristic equations (or dispersion relations) are deduced for the magnetostatic modes. Numerical calculations are presented for nanostructures of Ni and Ni80Fe20, which are ferromagnets, and MnF2 and GdAlO3, which are antiferromagnets. The radial amplitudes of the surface and bulk modes are also investigated.