Spin waves in permalloy nanowires: The importance of easy-plane anisotropy

Abstract

Brillouin light scattering has been employed to study the magnetic-field dependence of the discrete spin waves in permalloy ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ nanowires. When a small magnetic field is applied transverse to the nanowire, the results reveal a low-frequency mode, which is absent in the longitudinal case. A Hamiltonian-based microscopic theory for nanowires with inhomogeneous magnetization shows that the appearance of this mode, along with its higher-field behavior, is a significant consequence of a small easy-plane single-ion anisotropy at the nanowire surface. The calculations provide a good description of experimental data for both the transverse and longitudinal cases.