Lifetime, collapse and escape paths for hopfions in bulk magnets with competing exchange interactions

TL;DR

This study calculates the lifetimes and collapse pathways of magnetic hopfions in bulk magnets with competing exchange interactions, revealing their temperature-dependent stability and the significance of lattice effects on their collapse energies.

Contribution

It introduces a detailed analysis of hopfion lifetimes, collapse mechanisms, and escape paths considering lattice effects and different parameter sets within a discrete model.

Findings

Activation energies vary significantly with parameters.

Hopfions are stable only at very low temperatures.

Escape through boundaries requires no activation energy.

Abstract

The lifetimes of magnetic hopfions on a discrete lattice with competing exchange interactions are calculated within the framework of the transition state theory for magnetic degrees of freedom. Three sets of discrete model parameters corresponding to the same continuous micromagnetic model are considered. Minimal energy paths for hopfion collapses were found on the multidimensional energy surface of the system. The activation energies of the collapse processes have been calculated. It turned out that the activation energy differs significantly for the three considered values of the parameters, which indicates the importance of lattice effects, when the hopfion radius equals several lattice constants. Along with the collapse, the hopfion escape process through the sample boundary is studied. It is shown that this process does not require an activation energy. The lifetimes of hopfions are found and it is shown that they can exist only at temperatures of a few kelvins and practically cannot be generated due to thermal fluctuations.