Influence of a hot magnon gas on a bullet mode lifetime via incoherent interaction

The process of the rapid cooling of a nanometer thick magnetic film has been shown to lead to the transition of the hot magnon gas to Bose-Einstein condensate of magnons [1]. In the same film, a nonlinear bullet mode, having frequency below the minimum of the magnon spectrum, can be formed under continuous influence of external spin transfer torque. Although the bullet mode is quite unstable due to its nonlinear nature [3], the bullet mode lifetime (BML) might be much longer at the presence of a hot magnon gas [3] when compared to the BML in the state of thermodynamical equilibrium [2]. We developed a simple model of interaction of a nonlinear bullet mode with a hot magnon gas in the process of a rapid cooling. We demonstrated that the increase of the hot magnon gas temperature leads to the increase of the BML. A significant increase of the BML, which agrees with the experimental results [2], has been observed at the hot magnon gas temperature exceeding a certain critical value. The model developed demonstrates stabilization of the nonlinear bullet mode by incoherent interactions with a non-equilibrium magnon gas.

[1] M. Schneider et al., Nat. Nanotechnol. 15, 457 (2020).

[2] M. Schneider et al., arXiv:2106.14710 (2021).

[3] V. E. Demidov et al., Sci. Rep. 6, 32781 (2016).