A simple model for the description of Bose-Einstein condensation of magnons at room temperature

A Bose-Einstein condensate of magnons (mBEC) is formed in magnetic films under parametric pumping at room temperature [1] or by rapid cooling of a thin film [2]. There is a necessity to develop a simple theoretical model describing the main qualitative features of this macroscopic quantum phenomenon, while taking into account the non-local character of the dipole-dipole interaction determining the properties of the magnon spectra. We developed such an approximate model, and demonstrated that mBEC can be described as a gas of weakly-interacting bosonic quasi-particles with anisotropic effective mass in an infinite potential well formed by the ferromagnetic film. The anisotropy of the effective mass results in the anisotropy of the mBEC dynamical properties: the speed of the Bogolyubov’s waves [2] in mBEC is strongly dependent on the direction of the wave propagation. The developed model allows one to make accurate predictions about the nonlinear properties and stability of mBEC in different experimental conditions, the properties of the mBEC fluctuations, and characteristics of magnon density waves in mBEC.

[1] S.O. Demokritov et al., Nature 443, 430 (2006).
[2] M. Schneider et al., Nature Nanotechnology 15, 457(2020).
[3] D.A. Bozhko et al. , Nat. Commun. 10, 2460 (2019).