arXiv subjects

M. N. Potkina

Publications and source records attributed to M. N. Potkina.

4 recordsLinked to original sources

arXiv2026

Skyrmions in Synthetic Antiferromagnets: Collapse and Nucleation

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.

cond-mat.mtrl-sci↗

arXiv2021

Lifetime of skyrmions in discrete systems with infinitesimal lattice constant

Topological protection of chiral magnetic structures is investigated by taking a two-dimensional magnetic skyrmion as an example. The skyrmion lifetime is calculated based on harmonic transition state theory for a discrete lattice model using various values of the ratio of the lattice constant and the skyrmion size. Parameters of the system corresponding to exchange, anisotropy and Dzyaloshinsky-Moriya interaction are chosen in such a way as to keep the energy and size of the skyrmion unchanged for small values of the lattice constant, using scaling relations derived from continuous micromagnetic description. The number of magnetic moments included in the calculations reaches more than a million. The results indicate that in the limit of infinitesimal lattice constant, the energy barrier for skyrmion collapse approaches the Belavin-Polyakov lower bound of the energy of a topological soliton in the $σ$-model, the entropy contribution to the pre-exponential factor in the Arrhenius rate expression for collapse approaches a constant and the skyrmion lifetime can, for large enough number of spins, correspond to thermally stable skyrmion at room temperature even without magnetic dipole-dipole interaction.

cond-mat.mtrl-sci↗

arXiv2020

Stability of Long-lived Antiskyrmions in Mn-Pt-Sn Material

The lifetime of antiskyrmions at room temperature in a Mn-Pt-Sn tetragonal Heusler material has been calculated using an atomic scale representation including nearly a million spins. The evaluation of the pre-exponential factor in the Arrhenius rate expression for this large system is made possible by an implementation of harmonic transition state theory that avoids evaluation of the eigenvalues of the Hessian matrix.The parameter values in the extended Heisenberg Hamiltonian, including anisotropic Dzyaloshinskii-Moriya interaction, are chosen to reproduce experimental observations [A. K. Nayak $\it{et\,al.}$, Nature $\textbf{548}$, 561 (2017)], in particular the 150 nm diameter. The calculated results are consistent with the long lifetime observed in the laboratory and this exceptional stability of the antiskyrmions is found to result from large activation energy for collapse due to strong exchange coupling while the pre-exponential factor in the Arrhenius expression for the lifetime is found to have a typical magnitude of 10$^{-12}$ s, despite the large number of spins. The long lifetime is, therefore, found to result from energetic effects rather than entropic effects in this system.

cond-mat.mes-hall↗

arXiv2018

Topological Hall effect for electron scattering on skyrmions in external magnetic field

We consider topological Hall effect (THE) in thin ferromagnetic films due to electron scattering on magnetic skyrmions in the presence of the relatively strong external magnetic field. We account for the effect of the magnetic field on a skyrmion structure and describe the hallmarks of THE differentiating it from ordinary and anomalous Hall effects. We have found that, although in typical ferromagnets the variation of magnetic field in the range 1-5 T substantially affects the skyrmion size, THE changes rather weakly remaining quite robust. Therefore, the magnitude of THE is primarily determined by the skyrmions sheet density $n_{sk}$, being comparable to the magnitude of the ordinary Hall effect (OHE) at $n_{sk}=10^{11}$ cm$^{-2}$. The sign of THE is opposite to that of OHE for skyrmions with positive vorticity, while for antiskyrmions the signs are the same.

cond-mat.mes-hall↗