Stability of single skyrmionic bits

Abstract

The switching between topologically distinct skyrmionic and ferromagnetic states has been proposed as a bit operation for information storage. While long lifetimes of the bits are required for data storage devices, the lifetimes of skyrmions have not been addressed so far. Here we show by means of atomistic Monte Carlo simulations that the field-dependent mean lifetimes of the skyrmionic and ferromagnetic states have a high asymmetry with respect to the critical magnetic field, at which these lifetimes are identical. According to our calculations, the main reason for the enhanced stability of skyrmions is a different field dependence of skyrmionic and ferromagnetic activation energies and a lower attempt frequency of skyrmions rather than the height of energy barriers. We use this knowledge to propose a procedure for the determination of effective material parameters and the quantification of the Monte Carlo timescale from the comparison of theoretical and experimental data.

Complex magnetic phase diagram and skyrmion lifetime in an ultrathin film from atomistic simulations

“…[56] was published, also concerning the finite lifetime of skyrmions in the Pd/Fe/Ir(111) system. This study focuses on the FP→SkL region of the phase diagram in Fig.…”

Path to collapse for an isolated Néel skyrmion

“…In the continuous micromagnetic description within a three-dimensional world, the topological transition is realized by the injection of a topological singularity called Bloch point, where the continuity of magnetism is broken 15 . For skyrmions, nucleation and annihilation have been observed in various simulations 3,12,[20][21][22]24 under thermal fluctuations or spin transfer torque excitations, but a detailed mechanism is still missing to evidence the role of topology in the stability. Whereas a Bloch point cannot, strictly speaking, exist in two-dimensional samples, an equivalent process has been mentioned 12,21 but it is not clear how it relates to the intermediate configuration at the energy barrier.…”

“…Of course, the higher the temperature, the shorter the mean life time τ . An activation energy is extracted 22,24 from the Arrhenius law τ = τ 0 exp(∆E/k B T ). In our case, although the agreement is not perfect, indicating that such a law may be oversimplified (for example, no temperature dependence of τ 0 is included), it sets the order of magnitude of the energy barrier to ∆E = 26±4 meV and τ 0 = 0.22±0.1 ns (Fig.…”

Formation and stability of metastable skyrmionic spin structures with various topologies in an ultrathin film

“…This energy barrier strongly depends on the magnetic field and system parameters [52,53]. In order to examine the relative stability of the skyrmionic structures, we performed finite-temperature spin dynamics simulations-for the method see, e.g., Ref.…”