Microscopic spin-wave theory for yttrium-iron garnet films

TL;DR

This paper develops a microscopic quantum approach to calculate spin-wave spectra in yttrium-iron garnet thin films, incorporating dipolar interactions and comparing results with analytic and phenomenological models.

Contribution

It introduces an efficient microscopic method using a bosonic representation and numerical diagonalization to accurately compute YIG spin-wave spectra, including long-range dipolar effects.

Findings

Numerical spectra match experimental parameters.

Comparison shows agreement with Landau-Lifshitz predictions.

Method efficiently incorporates dipolar interactions.

Abstract

Motivated by recent experiments on thin films of the ferromagnetic insulator yttrium-iron garnet (YIG), we have developed an efficient microscopic approach to calculate the spin-wave spectra of these systems. We model the experimentally relevant magnon band of YIG using an effective quantum Heisenberg model on a cubic lattice with ferromagnetic nearest neighbor exchange and long-range dipole-dipole interactions. After a bosonization of the spin degrees of freedom via a Holstein-Primakoff transformation and a truncation at quadratic order in the bosons, we obtain the spin-wave spectra for experimentally relevant parameters without further approximation by numerical diagonalization, using efficient Ewald summation techniques to carry out the dipolar sums. We compare our numerical results with two different analytic approximations and with predictions based on the phenomenological Landau-Lifshitz equation.