Victor L. Mironov

Magnetic nanostructures






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Magnetic-force microscopy

of ferromagnetic nanostructures


Here we present some our recent results of magnetic nanostructures investigations by magnetic force microscopy methods



1. V.L.Mironov, B.A.Gribkov, A.A.Fraerman, S.A.Gusev, S.N.Vdovichev, I.R.Karetnikova, I.M.Nefedov, I.A.Shereshevsky - MFM probe control of magnetic vortex chirality in elliptical Co nanoparticles // Journal of Magnetism and Magnetic Materials, 312, 153-157 (2007). <PDF>

Magnetic force microscopy (MFM) methods were applied to investigate the peculiarities of magnetization distribution in elliptical 400 × 600 × 27 nm Co particles. Reversible transitions between the uniform and vortex states under inhomogeneous magnetic field of MFM probe were observed. Possibility to control the chirality of a magnetic vortex in these particles by MFM probe manipulation was shown.



Fig.  Changing of vortex chirality within a Co particle (central particle). (a) Constant height MFM image of the initial state with VS+ in the central particle. (b) MFM image obtained by scanning with variable height. (c) The final VS- state in the central particle.



2. A.A.Fraerman, B.A.Gribkov, S.A.Gusev, A.Yu.Klimov, V.L.Mironov, D.S.Nikitushkin, V.V.Rogov, S.N.Vdovichev, B.Hjorvarsson, H.Zabel - Magnetic force microscopy of helical states in multilayer nanomagnets. // Journal of Applied Physics, 103, 073916 1-4, (2008). <PDF>


We have used magnetic force microscopy (MFM) to investigate noncollinear helical states in multilayer nanomagnets, consisting of a stack of single domain ferromagnetic disks separated by insulating nonmagnetic spacers. The nanomagnets were fabricated from a [Co/ Si]  3 multilayer thin film structure by electron beam lithography and ion beam etching. The structural parameters (Co layer and spacer thicknesses) were optimized to obtain a clear spiral signature in the MFM contrast, taking into account the magnetostatic interaction between the layers. MFM contrast corresponding to the helical states with different helicities was observed for the optimized structure with Co layer thicknesses of 16, 11, and 8 nm, and with 3 nm Si spacer thickness.



Fig. (a) Noncollinear helical magnetic state in the three-layer nanomagnets. (b) Model MFM contrast distribution for triple nanodisk. (b) The experimental MFM image from triple 16, 11, and 8 nm Co nanodisk.



3. V.L.Mironov, B.A.Gribkov, S.N.Vdovichev, S.A.Gusev, A.A.Fraerman, O.L.Ermolaeva, A.B.Shubin, A.M.Alexeev, P.A.Zhdan and C.Binns - Magnetic force microscope tip induced remagnetization of CoPt nanodiscs with perpendicular anisotropy // Journal of Applied Physics, 106, 053911 1-8 (2009). <PDF>


We report on the results of a magnetic force microscopy investigation of remagnetization processes in arrays of CoPt nanodisks with diameters of 35 and 200 nm and a thickness of 9.8 nm fabricated by e-beam lithography and ion etching. The controllable magnetization reversal of individual CoPt nanodisks by the magnetic force microscope (MFM) tip-induced magnetic field was demonstrated. We observed experimentally two essentially different processes of tip-induced remagnetization. Magnetization reversal of 200 nm disks was observed when the probe moved across the particle while in case of 35 nm nanodisks one-touch remagnetization was realized. Micromagnetic modeling based on the Landau-Lifshitz-Gilbert (LLG) equation demonstrated that the tip-induced magnetization reversal occurs through the essentially inhomogeneous states. Computer simulations confirmed that in case of 200 nm disks the mechanism of embryo nucleation with reversed magnetization and further dynamic propagation following the probe moving across the particle was realized. On the other hand one-touch remagnetization of 35 nm disks occurs through the inhomogeneous vortexlike state. Micromagnetic LLG simulations showed that magnetization reversal in an inhomogeneous MFM probe field has a lower energy barrier in comparison with the mechanism of coherent rotation, which takes place in a homogeneous external magnetic field.



Fig. Step-by-step MFM tip-induced bit writing in the ordered array of 35 nm CoPt nanoparticles with perpendicular anisotropy.



4. V.L. Mironov, O.L. Ermolaeva, S.A. Gusev, A.Yu. Klimov, V.V. Rogov, B.A. Gribkov, O.G. Udalov, A.A. Fraerman, R. Marsh, C. Checkley, R. Shaikhaidarov, and V.T. Petrashov - Antivortex state in crosslike nanomagnets // Physical Review B, 81, 094436 1-5 (2010). <PDF>


We report on results of computer micromodelling of antivortex states in asymmetrical crosslike ferromagnetic nanoparticles and their practical realization. The arrays of cobalt crosses with 1 μm branches, 100 nm widths of the branches and 40 nm thicknesses, were fabricated using e-beam lithography and ion etching. Each branch of the cross was tapered at one end and bulbous at the other. The stable formation of antivortex magnetic states in these nanostructures during magnetization reversal was demonstrated experimentally using magnetic force microscopy.



Fig. (a) is the antivortex state (simulation) in cross-like nanomagnets. (b) The model (b) and experimental (c) MFM contrast distribution corresponding to the antivortex state of magnetization .



5. V.L. Mironov, O.L. Ermolaeva, E.V. Skorohodov, and A.Yu. Klimov - Field-controlled domain wall pinning-depinning effects in ferromagnetic nanowire-nanoislands system // Physical Review B, 85, 144418 1-9 (2012). <PDF>

We present the results of micromagnetic modeling and experimental investigations of field-driven domain wall pinning-depinning effects in a planar system consisting of a ferromagnetic nanowire and two ferromagnetic single-domain nanoislands (NIs). It was demonstrated that the magnitude of the depinning field strongly depends on the spatial configuration of magnetic moments in the NI subsystem. An algorithm for the external magnetic field commutation and independent switching of the NI moments that permits the realization of logical operations is discussed.



Fig. (a) - Nanowire-nanoparticles system. (b) and (c) - MFM images of domain wall in nanowire. 




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