November 07, 2022
Minneapolis, United States
Effect of nonuniform perpendicular anisotropy in ferromagnetic resonance spectra in magnetic nanorings and nanodisks
A study of the effect of a nonuniform perpendicular magnetic anisotropy on the magnetic configurations and on the ferromagnetic resonance (FMR) spectra in two systems
was performed by micromagnetic simulations, by applying a short magnetic pulse 1-3.
First system corresponds to magnetic nanorings of different widening with radial distribution of the perpendicular magnetic anisotropy (RPMA) 1. Both the resonant frequencies and the
number of peaks depend on the lower energy magnetization configuration 4 (figure 1) which in turn is a function of anisotropy gradient. Also, we compare the diagram between nanorings
with and without RPMA showing that the effects of the RPMA are relevant even for the narrowest ring of 10 nm wide 1.
The second system corresponds to nanodisks with radial distribution but with the center of the distributed anisotropy displaced from the center of the nanodisk (figure 2). This break on the
symmetry of the RPMA with respect to the disk center, allows several new magnetic configurations such as skyrmionium-like magnetic states and therefore the resonance spectra of FMR
have several new modes and peaks compared to non-breaking symmetry of RPMA.
The results show that by controlling the RPMA strength K of the anisotropy gradient, and its symmetry, several new resonance modes and magnetic configurations can be obtained for
instance, vortex, meron and knot states in nanorings and skyrmionum in nanodisks.
Authors acknowledge DICYT Grant 042131EM, PAI77190042, Fondecyt 1201491 and Basal AFB 180001.
1 Saavedra, E. et al. Effect of nonuniform perpendicular anisotropy in ferromagnetic resonance spectra in magnetic nanorings. Sci. Rep. 11, 14230 (2021).
2 McMichael, R.D. and Stiles, M.D. Magnetic normal modes of nanoelements. J. Appl. Phys. 97, 10J901 (2005).
3 Baker, A. et al. Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations. J. Magn. Magn. Mater. 421, 428 (2017).
4 Castro, M.A. et al. New magnetic states in nanorings created by anisotropy gradients. J. Magn. Magn. Mater. 484, 55–60 (2019).
Figure 1: a) Minimal energy configurations as a function of the RPMA strength K: I, II, and III correspond to vortex, knot and meron states respectively. b) Imaginary component of the dynamic susceptibility for R1 = 50 nm c) Spatial distribution of the amplitude for vortex (K =300 kJ/m3), knot (K = 350 kJ/m3) and meron (K = 450 kJ/m3), respectively.