Magnetic Resonance Force Microscopy









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MFM study of magnetic skyrmion lattice


Co/Pt multilayers with perpendicular magnetic anisotropy are irradiated by focused He ion beam to locally reduce the anisotropy value. The irradiated spots with a diameter of 100 nm are arranged in a square lattice with 200 nm period. The formation of the nonuniform periodic magnetic structure is observed without changes in the film topography. The spatial symmetry of the magnetic force microscopy signal and the specific shape of magnetization curves indicate the formation of the magnetic bubbles or magnetic vortices within the irradiated spot depending on the irradiation dose. The experimental data are in a good agreement with micromagnetic simulations of the system.



Fig. The MFM image of the samples at large (A and B) and small (C and D) radiation doses, respectively, in residual (A and C) and demagnetized (B and D) states. The scan area is 2 × 2 μm2.


M. V. Sapozhnikov, S. N. Vdovichev, O. L. Ermolaeva, N. S. Gusev, A. A. Fraerman, S. A. Gusev, and Yu. V. Petrov -Artificial dense lattice ofmagnetic bubbles, Applied Physics Letters, 109, 042406 (2016)   <pdf>


Ferromagnetic resonance in CoPt/Co system


We report a study of interlayer exchange interaction in multilayer [Co/Pt]n/Pt/Co structures. The structures consist of a periodic [Co/Pt]n multilayer film with a perpendicular anisotropy and a thick Co layer with an in-plane anisotropy. The subsystems are separated by a Pt spacer with variable thickness. The magnetooptical Kerr effect and the ferromagnetic resonance measurements show the essentially non-collinear state of magnetic moments of the layers and strong exchange coupling between the [Co/Pt]n and the Co subsystems. A simple model based on the Landau-Lifshitz-Gilbert equation shows that the exchange coupling is ferromagnetic. The exchange constant is estimated in this simple model. The estimated value is = 2 erg/cm2.



Fig. Hysteresis loops and angle dependences of the resonant fields of the CoPt/Co system.


E. S. Demidov, N. S. Gusev, L. I. Budarin, E. A. Karashtin, V. L. Mironov and A. A. Fraerman - Interlayer interaction in multilayer [Co/Pt]n/Pt/Co structures, Journal of Applied Physics, 120, 173901 1-4 (2016).   <pdf>


Ferromagnetic resonance in locally modified CoPt films


We study the dynamical properties of a magnetic film with spatially modulated perpendicular anisotropy by numerical simulations. Both topologically charged states (magnetic skyrmions) and uncharged uniform and nonuniform states are considered. The dependences of the ferromagnetic resonance (FMR) spectra on the geometry and material parameters of the system are analyzed. It is found that the spectra contain resonances of the localized and delocalized modes of the magnetization oscillations. In the case of nonuniform states the localized modes have the form of rotating magnetization distributions. The direction of the rotation depends on the local density of the toroidal moment of the state. The magnetic states with different FMR spectra can be easily switched by a temporary applying of a uniform external magnetic field that can be used in the tunable microwave devices.




Fig. Oscillation modes of CoPt modified regions.


M. V. Sapozhnikov, R. V. Gorev, E. A. Karashtin and V. L. Mironov  Spin-wave resonances of ferromagnetic films with spatially modulated anisotropy, Journal of Magnetism and Magnetic Materials, 466, 1-6 (2018).   <pdf>


Ferromagnetic resonance in interacting magnetic microstripes


The results of the micromagnetic simulation of forced oscillations of the magnetization in a system of two interacting microstrips located at an angle to each other have been presented. The ferromagnetic resonance spectra and the mode composition of resonant oscillations of the system have been investigated under the conditions of magnetostatic and exchange interactions between the microstrips. It has been shown that the magnetostatic interaction leads to the possibility of the excitation of in-phase and out-of-phase coupled oscillations of the magnetization of the microstrips. In the systems of exchange-coupled microstrips, there are intense resonances due to oscillations of the domain walls. The transformation of the ferromagnetic resonance spectrum and the change in the mode composition of resonant oscillations in different equilibrium configurations of the magnetization of the system have been discussed, as well as the conditions for the excitation of oscillations of different types depending on the direction of the microwave magnetic field.



Fig. Resonance oscillations of NiFe system of NiFe interacting microstripes with domain wall.


R.V. Gorev, E.V. Skorokhodov and V.L. Mironov – Ferromagnetic resonance in interacting magnetic microstripes, Physics of the Solid State, Vol. 58, No. 11, pp. 2212-2217 (2016).   <pdf>


Ferromagnetic resonance of a magnetostatically stabilized domain wall in a nanowire-nanoparticle planar system


The results of micromagnetic simulation of induced high-frequency magnetization oscillations in a planar ferromagnetic system composed of a magnetostatically coupled nanowire and nanoparticle are reported. The possibility of transformation of the spectrum of this system by introducing a domain wall stabilized with the magnetic field of the nanoparticle into the nanowire is discussed. The dependences of the frequency and amplitude of resonant oscillations of the domain wall on the geometric parameters of the system are analyzed.




Fig. FMR of transverse and vortex domain walls in nanowire.


R.V. Gorev, V.L. Mironov – Ferromagnetic resonance of a magnetostatically stabilized domain wall in a nanowire-nanoparticle planar system, Technical Physics Letters, Vol. 43, No. 3, pp. 254-257 (2017). <pdf>


Ferromagnetic resonance force microscopy of individual domain wall


We report on ferromagnetic resonance force microscopy (FMRFM) based investigations of the ferromagnetic resonance of a single domain wall (DW) in a V-shaped planar permalloy nanowire (NW) which is bent by 60[1]. A pronounced resonance associated with the DW is observed at 1.6 GHz. FMRFM imaging at the resonance frequency confirms the localization of the resonant mode in the DW area. The measured spectra and spatial distribution of the resonant signal are in good agreement with the results of micromagnetic modeling. Published by AIP Publishing.




A. Volodin, C. Van Haesendock, E. V. Skprpkhodov, R. V. Gorev, V. L. Mironov – Ferromagnetic resonance force microscopy of individual domain wall, Applied Physics Letters, 113, 122407, 1-4 (2018).   <pdf>


MRFM of dense array


The ferromagnetic resonance in an array of permalloy microstrips 3000 × 500 × 30 nm in size ordered on a rectangular grid 3.5 × 6 μm in size has been investigated by magnetic resonance force microscopy. The dependences of magnetic resonance force microscopy spectra of a sample on the probe–sample distance are analyzed. The possibility of detection of a ferromagnetic resonance spectrum of a single microstrip is demonstrated.



E.V. Skorokhodov, M.V. Sapozhnikov and V.L. Mironov – Magnetic Resonance Force Microscopy of a Permalloy Microstrip Array, Technical Physics Letters, Vol. 44, No. 3, pp. 203-206 (2018).   <pdf>



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