Annihilation mechanisms and lifetime of racetrack skyrmions

The skyrmion racetrack is a promising concept for future information technology. There, binary bits are carried by nanoscale spin swirls -- skyrmions -- driven along magnetic strips. Stability of the skyrmions is a critical issue for the realization of this technology. Here we evaluate the lifetime of skyrmions in a racetrack as a function of temperature and magnetic field using a combination of harmonic transition state theory, extended to include Goldstone modes, and an atomistic spin Hamiltonian parametrized from density functional theory calculations. We demonstrate that two mechanisms of skyrmion annihilation in a racetrack contribute to the skyrmion stability: At low external magnetic field, escape through the system boundary prevails, but a crossover field exists, above which the collapse in the interior becomes dominant. The calculated lifetime in a Pd/Fe bilayer on an Ir(111) substrate is found to be consistent with reported experimental measurements. Our results open the door for predictive simulations, free from empirical parameters, to aid the design of skyrmion-based information technology.