Skyrmion lifetime in ultrathin films

Malottki, Stephan von; Bessarab, Pavel F.; Haldar, Soumyajyoti; Delin, Anna; Heinze, Stefan

doi:10.1103/physrevb.99.060409

Cited by 56 publications

(69 citation statements)

References 37 publications

(57 reference statements)

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“…Typically, the lifetime is dominated by the energy barrier due to the exponential term. Recently, it has been reported that due to entropy the prefactor can vary drastically with external parameters, e.g., the magnetic field 52 , 53 . For bulk magnetic materials a change by 30 orders of magnitude 52 and for ultrathin films a variation of up to seven orders of magnitude have been found 53 .…”

Section: Discussionmentioning

confidence: 99%

Role of higher-order exchange interactions for skyrmion stability

et al. 2020

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Transition-metal interfaces and multilayers are a promising class of systems to realize nanometer-sized, stable magnetic skyrmions for future spintronic devices. For room temperature applications, it is crucial to understand the interactions which control the stability of isolated skyrmions. Typically, skyrmion properties are explained by the interplay of pair-wise exchange interactions, the Dzyaloshinskii-Moriya interaction and the magnetocrystalline anisotropy energy. Here, we demonstrate that higher-order exchange interactions – which have so far been neglected – can play a key role for the stability of skyrmions. We use an atomistic spin model parametrized from first-principles and compare three different ultrathin film systems. We consider all fourth-order exchange interactions and show that, in particular, the four-site four spin interaction has a large effect on the energy barrier preventing skyrmion and antiskyrmion collapse into the ferromagnetic state. Our work opens perspectives to stabilize topological spin structures even in the absence of Dzyaloshinskii-Moriya interaction.

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Section: Discussionmentioning

confidence: 99%

Role of higher-order exchange interactions for skyrmion stability

et al. 2020

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“…Fig. 10 shows the results for an external field varied between 3.5 T and 5 T and temperature between 2 K and 5 K. HTST as well as Langers theory, 60 which is closely related, have recently both been used to calculate skyrmion lifetimes, [61][62][63] showing that energy barriers are in general not enough to estimate the stability of metastable magnetic states.…”

Section: E Harmonic Transition-state Theorymentioning

confidence: 99%

Spirit : Multifunctional framework for atomistic spin simulations

et al. 2019

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The Spirit framework is designed for atomic scale spin simulations of magnetic systems of arbitrary geometry and magnetic structure, providing a graphical user interface with powerful visualizations and an easy to use scripting interface. An extended Heisenberg type spin-lattice Hamiltonian including competing exchange interactions between neighbors at arbitrary distance, higher-order exchange, Dzyaloshinskii-Moriya and dipole-dipole interactions is used to describe the energetics of a system of classical spins localised at atom positions. A variety of common simulations methods are implemented including Monte Carlo and various time evolution algorithms based on the Landau-Lifshitz-Gilbert equation of motion, which can be used to determine static ground state and metastable spin configurations, sample equilibrium and finite temperature thermodynamical properties of magnetic materials and nanostructures or calculate dynamical trajectories including spin torques induced by stochastic temperature or electric current. Methods for finding the mechanism and rate of thermally assisted transitions include the geodesic nudged elastic band method, which can be applied when both initial and final states are specified, and the minimum mode following method when only the initial state is given. The lifetime of magnetic states and rate of transitions can be evaluated within the harmonic approximation of transition-state theory. The framework offers performant CPU and GPU parallelizations. All methods are verified and applications to several systems, such as vortices, domain walls, skyrmions and bobbers are described.

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“…Nevertheless, in this context, the direct use of transition state theory to compile an overall reliable lifetime for any given structure seems ill-advised, as it is difficult to account for all possible mechanisms. As for the low activation energies and not particularly low attempt frequencies, we can once more relate them to the skyrmions being very small, and possessing only a few internal modes [26,37].…”

Section: B Conclusionmentioning

confidence: 99%

Paths to annihilation of first- and second-order (anti)skyrmions via (anti)meron nucleation on the frustrated square lattice

2019

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We study annihilation mechanisms of small first-and second-order skyrmions and antiskyrmions on the frustrated J 1 − J 2 − J 3 square lattice with broken inversion symmetry (DMI). We find that annihilation happens via the injection of the opposite topological charge in the form of meron or antimeron nucleation. Overall, the exchange frustration generates a complex energy landscape with not only many (meta)stable and unstable local energy solutions, but also many possible paths connecting them. Whenever possible, we compute the activation energy and attempt frequency for the annihilation of isolated topological defects. In particular, we compare the average lifetime of the antiskyrmion calculated with transition state theory with direct Langevin simulations, where an excellent agreement is obtained.

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Skyrmion lifetime in ultrathin films

Cited by 56 publications

References 37 publications

Role of higher-order exchange interactions for skyrmion stability

Role of higher-order exchange interactions for skyrmion stability

Spirit : Multifunctional framework for atomistic spin simulations

Paths to annihilation of first- and second-order (anti)skyrmions via (anti)meron nucleation on the frustrated square lattice

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