Interfacial Dzyaloshinskii-Moriya interaction (DMI) is experimentally investigated in Pt/Co/Pt multilayer films under strain. A strong variation (from 0.1 to 0.8 mJ/m 2 ) of the DMI constant is demonstrated at ±0.1% in-plane uniaxial deformation of the films. The anisotropic strain induces strong DMI anisotropy. The DMI constant perpendicular to the strain direction changes sign while the constant along the strain direction does not. Estimates are made showing that DMI manipulation with an electric field can be realized in hybrid ferroelectric/ferromagnetic systems. So, the observed effect opens the way to manipulate the DMI and eventually skyrmions with a voltage via a strainmediated magneto-electric coupling.

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.

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We report the experimental observation of magnetic skyrmion-like states in patterned ferromagnetic nanostructures consisting of perpendicular magnetized Co/Pt multilayer film exchange coupled with Co nanodisks in vortex state. The magnetic force microscopy and micromagnetic simulations show that depending on the magnitude of Co/Pt perpendicular anisotropy in these systems two different modes of skyrmion formation are realized.Magnetic skyrmion is a localized spin configuration demonstrating unusual topological and transport properties [1]. This state was predicted theoretically as the effect of Dzjaloshinskii-Moriya interaction in crystals without an inversion center [2][3][4]. Experimentally the skyrmion lattices were observed in some crystals (MnSi, FeGe and other) at low temperatures [5][6][7]. Now one of actual problem is to expand the class of magnetic materials suitable for realization of skyrmions stable at room temperature. Recently the formation of skyrmion-like states induced by magnetic vortex in artificial ferromagnetic nanostructures was considered theoretically in Ref. [8].In current letter we present the experimental realization of skyrmion-like states in Co/Pt multilayer films exchange coupled with Co nanodisks (Co/Pt-Co disk nanostructures).The initial thin film structures [Co (0.5 nm) / Pt (1 nm)] 5 (denoted further as Co/Pt) and [Co (0.5 nm) / Pt (1 nm)] 5 / Co (denoted further as Co/Pt-Co) was grown by DC magnetron sputtering on Si substrate with Ta (10 nm) / Pt (10 nm) buffer layer. The magnetic properties of Co/Pt and Co/Pt-Co thin film structures were investigated by magneto-optical Kerr effect (MOKE) and ferromagnetic resonance (FMR) methods. In experiments we used two Co/Pt structures differing by coercivity. First structure (structure I) had the coercive field H cI = 130 Oe and saturation field H sI = 210 Oe, while the second one (structure II) had coercive field H cII = 180 Oe and saturation field H sII = 300 Oe. The corresponding hysteresis curves are presented in Fig. 1a.Covering Co/Pt structures by Co layer with thickness Co t < 1.5 nm led to narrowing hysteresis loop and for Co t > 1.5 nm we registered the anhysteretic magnetization curves. For example, normalized MOKE remagnetization loop for the structure I covered by 20 nm Co layer is presented in Fig. 1b. The FMR measurements showed that Co/Pt-Co thin film structures consist of two coupled effective oscillators Co/Pt (easy axis anisotropy) and Co (easy plane anisotropy) with surface energy of exchange interaction J = 1.9 × 10 -3 J/m 2 and we believe that anhysteretic behavior of these structures with Co t >1.5 nm shows that easy plane anisotropy is dominant.Removing Co coating layer by ion etching with ion energy 200 eV does not destroy Co/Pt multilayer structure. The hysteresis loop for Co/Pt multilayer film after 20 nm Co coating removal is presented in Fig. 1c. The magnetic states and the magnetization reversal effects in these nanostructures were studied using a vacuum multimode magnetic force microscope (MFM)