Interplay between size and stability of magnetic skyrmions

Abstract

The relationship between the size and stability of isolated skyrmions in a magnetic monolayer is analyzed based on minimum energy path calculations and atomistic spin Hamiltonian. It is demonstrated that the energy barrier protecting the skyrmion from collapse to the ferromagnetic state is not uniquely defined by the skyrmion size, although these two properties as functions of relevant material parameters follow similar trends. Stability of nanoscale skyrmions can be enhanced by a concerted adjustment of material parameters. The proposed parameter transformation conserves the skyrmion size, but does not conserve the skyrmion shape which changes from an arrow-like pattern to a profile that resembles magnetic bubbles. This transformation of the skyrmion shape is accompanied by an increase in the collapse energy barrier and thus enhancement of skyrmion stability.

Universality of annihilation barriers of large magnetic skyrmions in chiral and frustrated magnets

“…2. In agreement with the previous study by Varentsova et al 26 , we observe that the annihilation barrier becomes larger when the Dzyaloshinskii-Moriya interaction D/J is smaller. As J/D determines the radius of the skyrmion, this also implies that larger skyrmions are more stable.…”

“…In Fig. 1 we have shown that the skyrmion shrinks before it collapses as has been discussed in numerous previous studies 12,15,16,20,21,26,27 . The main reason for the collapse is that the destruction of a skyrmion necessarily involves a singular, vortex-like spin configuration.…”

“…The snapshots of the spin-configuration obtained along the path, Fig. 1a-f, show that the decay can be described as the shrinking of the skyrmion along a so-called collapse path 12,15,16,20,21,26,27 . Our goal will be to obtain an analytic understanding of the value of the energy at the saddle point configuration, shown in Fig.…”

“…Here it was found that, typically, skyrmions decay via shrinking to the size of a lattice constant 15 if they cannot escape via the edge of the system 20,21 or decay via quantum mechanical tunnelling 37 . Furthermore, two distinct concepts were identified that lead to higher energy barriers and, hence, more stable skyrmions: larger energy barriers were obtained for larger skyrmions 26,36 while the energy barrier of smaller skyrmions was found to be increased by frustrating next-nearest neighbor exchange interactions 22 . For a particular case of the latter scenario, in contrast to the symmetric shrinking path, an asymmetric decay path was reported 35 where the skyrmion annihilates via a singular defect at an off-center position.…”

Skyrmion lifetime in ultrathin films

“…(1) suggests that control over the energy barrier should be the key strategy for improving on thermal stability of skyrmions. Recent theoretical works have indeed focused on obtaining the energy barrier of skyrmion annihiliation [10][11][12][13][14][15][16][17][18][19][20]. For decades, tuning the energy barrier has been the main approach to the development of information storage bits based on magnetic materials.…”