Magnetic Direct-Write Skyrmion Nanolithography.

Magnetic skyrmions are stable spin textures with quasi-particle behavior and attract significant interest in fundamental and applied physics. The metastability of magnetic skyrmions at zero magnetic field is particularly important to enable, for instance, a skyrmion racetrack memory. Here, the results of the nucleation of stable skyrmions and formation of ordered skyrmion lattices by magnetic force microscopy in (Pt/CoFeSiB/W)n multilayers, exploiting the additive effect of the interfacial Dzyaloshinskii-Moriya interaction, are presented. The appropriate conditions under which skyrmion lattices are confined with a dense two-dimensional liquid phase are identified. A crucial parameter to control the skyrmion lattice characteristics and the number of scans resulting in the complete formation of a skyrmion lattice is the distance between two adjacent scanning lines of a magnetic force microscopy probe. The creation of skyrmion patterns with complex geometry is demonstrated, and the physical mechanism of direct magnetic writing of skyrmions is comprehended by micromagnetic simulations. This study shows a potential of a direct-write (maskless) skyrmion (topological) nanolithography with sub-100 nm resolution, where each skyrmion acts as a pixel in the final topological image.

Composite topological structure of domain walls in synthetic antiferromagnets.

We experimentally study the structure and dynamics of magnetic domains in synthetic antiferromagnets based on Co/Ru/Co films. Dramatic effects arise from the interaction among the topological defects comprising the dual domain walls in these structures. Under applied magnetic fields, the dual domain walls propagate following the dynamics of bi-meronic (bi-vortex/bi-antivortex) topological defects built in the walls. Application of an external field triggers a rich dynamical response: The propagation depends on mutual orientation and chirality of bi-vortices and bi-antivortices in the domain walls. For certain configurations, we observe sudden jumps of composite domain walls in increasing field, which are associated with the decay of composite skyrmions. These features allow for the enhanced control of domain-wall motion in synthetic antiferromagnets with the potential of employing them as information carriers in future logic and storage devices.

Vortex dynamics and frequency splitting in vertically coupled nanomagnets.

We explored the dynamic response of a vortex core in a circular nanomagnet by manipulating its dipole-dipole interaction with another vortex core confined locally on top of the nanomagnet. A clear frequency splitting is observed corresponding to the gyrofrequencies of the two vortex cores. The peak positions of the two resonance frequencies can be engineered by controlling the magnitude and direction of the external magnetic field. Both experimental and micromagnetic simulations show that the frequency spectra for the combined system is significantly dependent on the chirality of the circular nanomagnet and is asymmetric with respect to the external bias field. We attribute this result to the strong dynamic dipole-dipole interaction between the two vortex cores, which varies with the distance between them. The possibility of having multiple states in a single nanomagnet with vertical coupling could be of interest for magnetoresistive memories.

Self-organization and FORC-based magnetic characterization of ultra-high aspect ratio epitaxial Co nanostrips produced by oblique deposition on an ordered step-bunched silicon surface.

Further development of microelectronics requires novel or improved technological approaches for device nanofabrication and functional properties characterization. In this paper, we studied the crystal structure and magnetic properties of epitaxial Co nanostrips with the average width of 32.6, 45.3, and 62.6 nm grown on a step-bunched Si(111)5.55 × 5.55-Cu/Cu surface. Technological conditions, under which the ultra-high aspect ratio (∼104) structurally solid, straight nanostrips of hcp-Co with crystallographic axis [0001] oriented along their long side can be grown, were determined. The dependence of the coercive force on the width of the nanostrips was demonstrated. Magnetization reversal through the transverse domain-wall nucleation and propagation in a Co nanostrip was defined with an analytical approach based on the Stoner-Wohlfarth model. Using the first-order reversal curve method, we analyzed the effect of nanostrip uniformity degree on magnetic behavior and the influence of the magnetostatic interactions on the coercive force of individual nanostrips.