On the theory of Bose-Einstein condensation of quasiparticles: on the possibility of condensation of magnons at high temperatures

TL;DR

This paper explores the possibility of Bose-Einstein condensation of magnons in ferromagnetic thin films at relatively high temperatures around 100 K, highlighting the influence of quasiparticle density, spectrum shape, and film thickness.

Contribution

It demonstrates that magnon Bose condensation can occur at higher temperatures than previously thought, with a focus on finite-size effects and experimental feasibility.

Findings

Condensation begins at T~100 K in ferromagnetic films.

Scaling phenomenon: main variable is N/T, not N.

Condensation possible at low magnon densities.

Abstract

Bose condensation of quasiparticles in physical systems of finite size iz considered for the case of ferromagnetic thin films. It is shown that in accordance with present-day experimental capabilities which permit one to achieve densities of long-wave spin excitation of 1018-1019 cm-3, in such films the formation of condensate of such quasiparticles begins at temperatures T~100 K (room one including). It is found that Bose condensation is accompanied by scaling phenomenon according to which the main thermodynamic variable is not the number N of particles but the ratio N/T. This indicates that condensation of magnons can be observed at relatively low magnon densities. The roles played by the shape of the spectrum and film thickness are analyzed.