Maxim E. Stebliy

3-D Architectural Approach for Manipulation of the Micromagnetic Configuration in Nanodisks

We report on novel method of manipulation of the micromagnetic configuration realized in 3-D nanostructures “small disk on the big disk”. Our method allows to control vortex chirality in a submicrometer magnetic disk without use of its deformation or defects of shape. Manipulation is performed by means of the fabrication on the top of disk a smaller disk with a diameter 200 nm. This paper shows that it is possible to explicitly set the magnetization direction of the small disk. Thus, the proposed system has four stable magnetic configurations that are uniquely specified by the direction of an external magnetic field.

Vortex manipulation and chirality control in asymmetric bilayer nanomagnets

This paper presents a method of controlling the chirality of magnetic vortex in a permalloy nanodisk having a cobalt nanostripe at the top. Features of magnetization reversal of the disk + stripe nanostructure are investigated using the magneto-optical Kerr effect magnetometer and magnetic force microscope. Micromagnetic simulations reveal peculiarities in the vortex nucleation process and in trajectory of the vortex core under the impact of external magnetic fields.

Magnetic Behavior of Single Ni Nanowires and its Arrays Embedded in Highly Ordered Nanoporous Alumina Templates

We report on magnetization reversal and geometry dependent magnetic anisotropy of Ni nanowire arrays electrodeposited in nanoporous alumina templates. Using micromagnetic simulation we have found that magnetization reversal mechanism in arrays with different nanowire diameters is curling. This magnetic behavior appears with propagation of the domain wall along a nanowire. The calculations have been proven by the analysis of hysteresis curves. To explain magnetic properties of closely-spaced nanowire arrays we have taken into consideration the magnetostatic interaction between adjacent nanowires and their structural defects, like as boundary grains. The investigated magnetic domain pattern of individual bended nanowires confirms rather complicated magnetization reversal mechanism than either coherent rotation of magnetization or its curling. Competition between the shape and magnetoelastic anisotropies can induce an unusual zigzag-like domain pattern in a single nanowire.

Magnetoresistive properties of the “small disk on a big disk” nanostructure

Magnetotransport properties of three-dimensional (3D) nano-sized structure with “small disk on a big disk” architecture are represented in this paper. We demonstrate an approach to analyze the spin configuration formed in the disks using magnetoresistance measurement. The behavior of magnetoresistance depends on the orientation of the applied magnetic field with respect to an axis connecting the centers of disks. This is explained by field dependent magnetic vortex nucleation and movement processes in the big disk. The experimental results are confirmed by the micromagnetic simulation of magnetoresistance loops.

Experimental evidence of skyrmion-like configurations in bilayer nanodisks with perpendicular magnetic anisotropy

Formation and existence of magnetic skyrmion-like configurations in bilayer nanodisks {Ta(3 nm)/[Co(0.37 nm)/Ni(0.58 nm)]10}2 with perpendicular magnetic anisotropy are shown experimentally at room temperature. Magnetization reversal through the skyrmion state is studied using magnetic hysteresis measurements. An evolution of skyrmion configurations in the nanodisk structure is analyzed. Experimental methods and micromagnetic simulations help to understand the magnetization reversal processes occurring through the stable skyrmion-like configurations. Formation of the intermediate C-states during magnetization reversal is demonstrated. The skyrmion number for all possible spin configurations is calculated.

Manipulation of magnetic vortex parameters in disk-on-disk nanostructures with various geometry

Summary Magnetic nanostructures in the form of a sandwich consisting of two permalloy (Py) disks with diameters of 600 and 200 nm separated by a nonmagnetic interlayer are studied. Magnetization reversal of the disk-on-disk nanostructures depends on the distance between centers of the small and big disks and on orientation of an external magnetic field applied during measurements. It is found that manipulation of the magnetic vortex chirality and the trajectory of the vortex core in the big disk is only possible in asymmetric nanostructures. Experimentally studied peculiarities of a motion path of the vortex core and vortex parameters by the magneto-optical Kerr effect (MOKE) magnetometer are supported by the magnetic force microscopy imaging and micromagnetic simulations.

An influence of mechanical deformations on crystal structure and spin configuration in magnetic nanowires

The influence of strain induced into individual fine-grain Ni nanowires on crystalline and magnetic structures is discussed in this paper. Using transmission electron microscopy, we have found that the crystal twinning occurs in the strained parts of the nanowires. Changes in crystalline structure due to the mechanical deformations induce a magnetic anisotropy, which leads to a transverse magnetic structure.

Indirect exchange coupling driven magnetization switching of CoNi/Cu/CoPt pseudo spin-valves with perpendicular magnetic anisot-ropy

Magnetic nanostructures with perpendicular magnetic anisotropy (PMA), as compared with the spin valves with in-plane anisotropy, have a lower level of thermal magnetization noise due to the high value of PMA, as well as a lower critical current density required for magnetization reversal nanostructures [1, 2].

Magnetic properties of laser welded coatings from Sm and Fe powders with and without magnetic field on Al based substrate

Two step laser’s welding of Sm and Fe powders on duralumin substrate in the argon gas flow has been firstly tested. It was established that oxidation of Sm atoms with formation of Sm2O3 and SmO during laser welding of duralumin substrate is the main reason of not forming of the SmFex compound, which can be appeared on the second step of Fe laser welding. The next reason is a strong interaction between Al and Sm atoms at the interface with a substrate with formation of Al2Sm compound, consisting from paramagnetic atoms. So, an additional protection from oxidation needs during laser welding. Magnetic properties of coatings formed by layer-by-layer laser welding from Sm and Fe powders on duralumin AMg-3 substrate welded with and without external magnetic field have been studied by methods of field and temperature magnetization measurements and study by vibromagnetometer method at room temperature (300 K). A strong paramagnetic contribution of AMg-3 substrate has been proved. Al2Sm grains without substrate have shown soft ferromagnetic properties at 300 K independently from using an external magnetic field. An interesting phenomenon has been found at cooling coatings down to 4 K: magnetic ordering of Al2Sm domains with Curie temperature about 70 K.

An influence of formation methods of laser layer’s welding on their phase composition and magnetic properties

Comparative study of laser welding method has been carried out at four different methods of welding in Sm-Co system on two types of substrates: stainless steel and duralumin and at two types of argon gas flow in the place of melting. The comparison of compositions and magnetic properties of welded coatings has been done for all formed samples. It was established that SmCo8.5 compound conserves only after laser welding of SmCo8.5 tablets with additional contribution of oxides that results to strongly decrease of saturation magnetization and coercivity as compared with SmCo8.5 films. In the case of the standard argon gas flow and using of Sm and Co powders the quick melting of the stainless steel substrate surface occurs that results to strong diffusion of transition metals to the welded layer and formation of Sm-based, noncrystalline alloy with only two crystalline phases (Co0.72Fe0.28 and Co), which demonstrate soft ferromagnetic properties. The formation of Sm-Co chemical compound is blocked when the Co welding carried out after Sm welding due to formation of Sm oxides on the welding surface. In the conditions of a stable argon atmosphere around the sample the pure Co and Sm crystals have been formed with weak ferromagnetic properties.