Skyrmion collapse and nucleation in synthetic antiferromagnet islands with pinned boundaries

Magnetic skyrmions in synthetic antiferromagnets are promising nanoscale bits, but their usefulness depends on how reliably a written pair survives and can be created. Using a reduced lattice model, we compute minimum energy paths for collapse of an antiferromagnetically bound skyrmion pair and for reverse nucleation from a pinned antiferromagnetic reference state. With antiferromagnetically pinned boundaries, the main saddle energy changes only weakly with pinned-island size, whereas the skyrmion-pair minimum carries a strong size-dependent boundary penalty. For large pinned islands, collapse is layer-sequential and can pass through a single-layer skyrmion intermediate whenever this state satisfies the relaxation criterion. The much larger reverse barrier for nucleation shows a strong asymmetry with collapse in the same pinned-boundary model and is consistent with assisted layer-sequential writing.

1. Wiesendanger R. Nanoscale magnetic skyrmions in metallic films and multilayers: a new twist for spintronics. Nat. Rev. Mater., 2016, 1, P. 16044.

2. Finocchio G., Bu¨ttner F., Tomasello R., Carpentieri M., Kla¨ui M. Magnetic skyrmions: from fundamental to applications. J. Phys. D: Appl. Phys., 2016, 49, P. 423001.

3. Fert A., Reyren N., Cros V. Magnetic skyrmions: advances in physics and potential applications. Nat. Rev. Mater., 2017, 2, P. 17031.

4. Bu¨ttner F., Lemesh I., Beach G.S.D. Theory of isolated magnetic skyrmions: from fundamentals to room temperature applications. Sci. Rep., 2018, 8, P. 4464.

5. Caretta L., Mann M., Bu¨ttner F., Ueda K., Pfau B., Gu¨nther C.M., Hessing P., Churikova A., Klose C., Schneider M., Engel D., Marcus C., Bono D., Bagschik K., Eisebitt S., Beach G.S.D. Fast current-driven domain walls and small skyrmions in a compensated ferrimagnet. Nat. Nanotechnol., 2018, 13, P. 1154.

6. Potkina M.N., Lobanov I.S., Jo´nsson H., Uzdin V.M. Skyrmions in antiferromagnets: thermal stability and the effect of external field and impurities. J. Appl. Phys., 2020, 127, P. 213906.

7. Duine R.A., Lee K.-J., Parkin S.S.P., Stiles M.D. Synthetic antiferromagnetic spintronics. Nat. Phys., 2018, 14, P. 217.

8. Zhang X., Ezawa M., Zhou Y. Thermally stable magnetic skyrmions in multilayer synthetic antiferromagnetic racetracks. Phys. Rev. B, 2016, 94, P. 064406.

9. Koshibae W., Nagaosa N. Theory of skyrmions in bilayer systems. Sci. Rep., 2017, 7, P. 42645.

10. Li Y., Feng Q., Li S., Huang K., Ma M., Gan W., Zhou H., Jin X., Wang X.R., Lu Y., Lew W.S. An artificial skyrmion platform with robust tunability in synthetic antiferromagnetic multilayers. Adv. Funct. Mater., 2020, 30, P. 1907140.

11. Dohi T., DuttaGupta S., Fukami S., Ohno H. Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles. Nat. Commun., 2019, 10, P. 5153.

12. Legrand W., Maccariello D., Ajejas F., Collin S., Vecchiola A., Bouzehouane K., Reyren N., Cros V., Fert A. Room-temperature stabilization of antiferromagnetic skyrmions in synthetic antiferromagnets. Nat. Mater., 2020, 19, P. 34.

13. Chen R., Gao Y., Zhang X., Zhang R., Yin S., Chen X., Zhou X., Zhou Y., Xia J., Zhou Y., Wang S. Realization of isolated and high-density skyrmions at room temperature in uncompensated synthetic antiferromagnets. Nano Lett., 2020, 20, P. 3299.

14. Jia H., Zimmermann B., Hoffmann M., Sallermann M., Bihlmayer G., Blu¨gel S. Material systems for FM-/AFM-coupled skyrmions in Co/Pt-based multilayers. Phys. Rev. Mater., 2020, 4, P. 094407.

15. Juge R., Sisodia N., Urrestarazu-Larran˜aga J., Zhang Q., Pham V. T., Rana K. G., Sarpi B., Mille N., Stanescu S., Belkhou R., Mawass M.-A., Novakovic-Marinkovic N., Kronast F., Weigand M., Gra¨fe J., Wintz S., Finizio S., Raabe J., Aballe L., Foerster M., Belmeguenai M., Buda-Prejbeanu L.D., Shaw J.M., Nembach H.T., Ranno L., Gaudin G., Boulle O. Skyrmions in synthetic antiferromagnets and their nucleation via electrical current and ultra-fast laser illumination. Nat. Commun., 2022, 13, P. 4807.

16. Pham V.T., Sisodia N., Di Manici I., Urrestarazu-Larran˜aga J., Bairagi K., Pelloux-Prayer J., Guedas R., Buda-Prejbeanu L.D., Auffret S., Locatelli A., Mentes T.O., Pizzini S., Kumar P., Finco A., Jacques V., Gaudin G., Boulle O. Fast current-induced skyrmion motion in synthetic antiferromagnets. Science, 2024, 384, P. 307.

17. Qiu S., Liu J., Chen Y., Qi X., Fang L. Writing skyrmion at a specific position in synthetic antiferromagnetic racetrack by voltage. J. Magn. Magn. Mater., 2022, 554, P. 169144.

18. Chen R., Cui Q., Han L., Xue X., Liang J., Bai H., Zhou Y., Pan F., Yang H., Song C. Controllable generation of antiferromagnetic skyrmions in synthetic antiferromagnets with thermal effect. Adv. Funct. Mater., 2022, 32, P. 2111906.

19. Potkina M.N., Lobanov I.S., Uzdin V.M. Nonmagnetic impurities in skyrmion racetrack memory. Nanosyst. Phys. Chem. Math., 2020, 11, P. 628– 635.

20. Potkina M.N., Lobanov I.S. Nucleation of magnetic skyrmions at a notch. Nanosyst. Phys. Chem. Math., 2024, 15, P. 192–200.

21. Potkina M.N., Lobanov I.S. Optimality of linear vacancy defect for skyrmion nucleation. Nanosyst. Phys. Chem. Math., 2025, 16, P. 317–324.

22. Deng P., Zhuo F., Li H., Cheng Z. Mirroring skyrmions in synthetic antiferromagnets via modular design. Nanomaterials, 2023, 13, P. 859.

23. Lobanov I.S., Potkina M.N., Uzdin V.M. Stability and lifetimes of magnetic states of nanoand microstructures (brief review). JETP Lett., 2021, 113, P. 801.

24. Lobanov I.S., Uzdin V.M. The lifetime of micron scale topological chiral magnetic states with atomic resolution. Comput. Phys. Commun., 2021, 269, P. 108136.

25. Varentsova A.S., Potkina M.N., von Malottki S., Heinze S., Bessarab P.F. Interplay between size and stability of magnetic skyrmions. Nanosyst. Phys. Chem. Math., 2018, 9, P. 356–363.

26. Potkina M.N., Lobanov I.S., Uzdin V.M. Nucleation and collapse of magnetic topological solitons in external magnetic field. Nanosyst. Phys. Chem. Math., 2023, 14, P. 216–222.

27. Schrautzer H., von Malottki S., Bessarab P.F., Heinze S. Effects of interlayer exchange on collapse mechanisms and stability of magnetic skyrmions. Phys. Rev. B, 2022, 105, P. 014414.

28. Voronin K.V., Lobanov I.S., Uzdin V.M. Activation energy and mechanisms for skyrmion collapse in synthetic antiferromagnets. JETP Lett., 2022, 116, P. 240–245.

29. Correia M.V., Pina Velasquez J.C., de Souza Silva C.C. Stability and dynamics of synthetic antiferromagnetic skyrmions in asymmetric multilayers. Phys. Rev. B, 2024 110, P. 094430.

30. Bessarab P.F., Uzdin V.M., Jo´nsson H. Method for finding mechanism and activation energy of magnetic transitions, applied to skyrmion and antivortex annihilation. Comput. Phys. Commun., 2015 196, P. 335–347.

31. Lobanov I.S., Potkina M.N., Jo´nsson H., Uzdin V.M. Truncated minimum energy path method for finding first order saddle points. Nanosyst. Phys. Chem. Math., 2017, 8, P. 586–595.