Analysis of stability and transition dynamics of skyrmions and skyrmioniums in ferromagnetic nanodisks: A micromagnetic study at finite temperature

Understanding the stability of skyrmions and skyrmioniums is crucial for potential applications, as thermal fluctuations can cause them to transform into other magnetic structures. In this study, we used micromagnetic simulations to examine the regions of stable existence for skyrmion and skyrmionium structures in Co/Pt ferromagnetic nanodisks at 300 K and beyond. We identified stability regions for different values of anisotropy energy (${K}_{z}$) and interfacial Dzyaloshinskii-Moriya interaction (DMI). Interestingly, these structures share a mutual region of stability. Depending on the thermal energy system, transitions can occur from skyrmionium to skyrmion. We further compute the corresponding thermal activation energy barrier for this transition as $\mathrm{\ensuremath{\Delta}}E/{k}_{B}=(15\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}{10}^{2} \mathrm{K}$, with an average lifetime of ${\ensuremath{\tau}}_{0}$ = 0.9 $\ifmmode\pm\else\textpm\fi{}$ 0.4 ns. This transition can also be triggered by a magnetic field applied along the $z$-axis.