We report an experimental study of the optical properties of a two-dimensional square lattice of triangle Co and CoFe nanoparticles with a vortex magnetization distribution. We demonstrate that the intensity of light scattered in the diffraction maxima depends on the vorticity of the particles' magnetization and can be manipulated by applying an external magnetic field. The experimental results can be understood in terms of simple phenomenological consideration.

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We present the results of systematic experimental investigations and micromagnetic simulations for the ferromagnetic resonance in rectangular permalloy microstripes. It is shown that the resonant magnetization oscillations have a complex spatial structure including a quasi-homogeneous precession, lateral spin-wave resonances and localized edge modes, which strongly depend on sample orientation in an external magnetic field.

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)

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Abstract:We present the results of magnetic force microscopy investigations of domain structures in multilayer [Co (0.5 nm)/Pt (1 nm)] 5 thin film structures (denoted hereafter as Co/Pt) modified by additional Co capping layers and by ion irradiation. It is demonstrated that a Co capping layer essentially changes the domain structure and decreases the threshold of magnetization reversal, due to the formation of noncollinear magnetization in Co/Pt. It is shown that local irradiation with a focused He + ion beam enables the formation of regions with decreased easy-axis anisotropy (magnetic bubbles) that have the inverse magnetization direction in the demagnetized state of Co/Pt. The experimental results demonstrate that the magnetic bubbles can be switched using a probe of a magnetic force microscope. The possible application of these effects for the development of magnetic logic and data storage systems is discussed.

We present a theoretical investigation of magnetostatic interaction effects in geometrically frustrated arrays of anisotropic multilayer ferromagnetic nanoparticles arranged in different spatially configured systems with triangular symmetry. We show that the interlayer magnetostatic interaction significantly expands the opportunities to create magnetically frustrated systems. The effects of the magnetostatic interaction in magnetization reversal processes and the possibility to control the ferromagnetic resonance spectrum in such systems are discussed.