Rannsóknir á staðbundnu segulástandi með tölvureikningum - verkefni lokið
Fréttatilkynning verkefnisstjóra
The aim of the project was to study the stability of magnetic chiral structures with respect to thermal fluctuations in the framework of the harmonic transition state theory for magnetic degrees of freedom.
Magnetic skyrmions are promising candidates as a basis for ultradense and fast memory devices due to their small size and high mobility. In such devices, it is important to be able to assess the stability of structures against thermal fluctuations and random external influences. One of the tasks of the project was to study skyrmions in
antiferromagnets (AFM). A different character of the dependence of the transition rate and radii of AFM and ferromagnetic (FM) skyrmions on the magnetic field is revealed. It was shown that a non-magnetic impurity or defect is less likely to trap a skyrmion in an AFM than in FM material. An explanation was obtained for the different values of the lifetimes in the two types of materials. We also calculated the lifetime of antiskyrmions experimentally observed at room temperature, and it was concluded that the high stability in this system is a consequence of the high activation energy.
In this project we studied the stability of the skyrmion as a function of the material parameters – Dzyaloshinskii-Moriya interaction and the anisotropy constant. A transformation of these parameters was found under which the lifetime of the skyrmion increases, and its size is constant. This result yields guiding principle for the realization of nanoscale, roomtemperature stable skyrmions for the future memory devices. For a skyrmion in the racetrack memory device, it is necessary to take into account the influence of boundaries on its stability. The task was to study the stability of skyrmions under conditions of constricted geometry, as well as under the influence of a magnetic field. The rates of transitions for the collapse of the skyrmion inside the track and escape through its boundary in various magnetic fields were calculated. Another issue for skyrmion application in racetrack devices is inevitable presence of defects. We investigated processes of attachment and detachment of skyrmions from defects, collapse and nucleation of skyrmions pinned to a nonmagnetic impurity on a track of finite width. Analysis of joint effect of track boundary and defects on skyrmion allowed us to determine the smallest track width and largest impurity size permissible in future racetrack memory devices.
The results of the project provide a deeper understanding of the stability of chiral magnetic
structures against thermal fluctuations and are the next step towards creating a new
generation of spintronic devices.
A list of the project’s outputs
List of publications:
M.N. Potkina, I.S. Lobanov, H. Jónsson, V. M. Uzdin, Skyrmions in antiferromagnets:
Thermal stability and the effect of external field and impurities, Journal of Applied Physics,
127, 213906 (2020)
M. N. Potkina, I.S. Lobanov, O. A. Tretiakov, H. Jónsson, V. M. Uzdin, Stability of Long-lived
Antiskyrmions in Mn-Pt-Sn Material, Physical Review B, 102, 134430 (2020)
Anastasiia S. Varentcova, Stephan von Malottki, Maria N. Potkina, Grzegorz Kwiatkowski,
Stefan Heinze, Pavel F. Bessarab, Towards room temperature nanoscale skyrmions in
ultrathin films, npj Comput Mater, 6, 193 (2020)
V. M. Uzdin, M.N. Potkina, I.S. Lobanov, P.F. Bessarab, H. Jónsson, The effect of
confinement and defects on the thermal stability of skyrmions, Physica B, 549, 6-9 (2018)
V. M. Uzdin, M.N. Potkina, I.S. Lobanov, P.F. Bessarab, H. Jónsson, Energy surface and
lifetime of magnetic skyrmions, J. Magn. Magn. Mat., 459-, 236-240 (2018)
M. N. Potkina, I. S. Lobanov, V. M. Uzdin, Nonmagnetic impurities in skyrmion racetrack
memory, Nanosystems: Physics, Chemistry, Mathematics. 11 (6), 628–635 (2020)
K. S. Denisov, I. V. Rozhansky, M. N. Potkina, I. S. Lobanov, E. Lähderanta, and V. M. Uzdin,
Topological Hall effect for electron scattering on nanoscale skyrmions in external magnetic
field, Physical Review B 98, 214407 (2018)
S. M. Vlasov, P.F. Bessarab, I.S. Lobanov, M.N. Potkina, V. M. Uzdin, H. Jónsson, Magnetic
skyrmion annihilation by quantum mechanical tunneling, New Journal of Physics, 22, 083013
(2020)
Heiti verkefnis: Rannsóknir
á staðbundnu segulástandi með tölvureikningum/Simulation studies of local
magnetic structures in antiferromagnets
Verkefnisstjóri: Maria Potkina, Raunvísindastofnun
Tegund styrks: Doktorsnemastyrkur
Styrktímabil: 2018-2020
Fjárhæð styrks: 19,8 millj. kr. alls
Tilvísunarnúmer Rannís: 185409
