Alexander G. Kolesnikov

Enhanced interfacial Dzyaloshinskii-Moriya interaction and isolated skyrmions in the inversion-symmetry-broken Ru/Co/W/Ru films

An enhancement of the spin-orbit effects arising on an interface between a ferromagnet (FM) and a heavy metal (HM) is possible through the strong breaking of the structural inversion symmetry in the layered films. Here, we show that an introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and simultaneously induce a large interfacial Dzyaloshinskii-Moriya interaction (iDMI). The study of the spin-wave propagation in the Damon-Eshbach geometry by Brillouin light scattering spectroscopy reveals the drastic increase in the iDMI value with the increase in W thickness (tW). The maximum iDMI of −3.1 erg/cm2 is observed for tW = 0.24 nm, which is 10 times larger than for the quasi-symmetrical Ru/Co/Ru films. We demonstrate the evidence of the spontaneous field-driven nucleation of isolated skyrmions supported by micromagnetic simulations. Magnetic force microscopy measurements reveal the existence of sub-100-nm skyrmions in the zero magnetic field. The ability to simultaneously control the strength of PMA and iDMI in quasi-symmetrical HM/FM/HM trilayer systems through the interface engineered inversion asymmetry at the nanoscale excites new fundamental and practical interest in ultrathin ferromagnets, which are a potential host for stable magnetic skyrmions.An enhancement of the spin-orbit effects arising on an interface between a ferromagnet (FM) and a heavy metal (HM) is possible through the strong breaking of the structural inversion symmetry in the layered films. Here, we show that an introduction of an ultrathin W interlayer between Co and Ru in Ru/Co/Ru films enables to preserve perpendicular magnetic anisotropy (PMA) and simultaneously induce a large interfacial Dzyaloshinskii-Moriya interaction (iDMI). The study of the spin-wave propagation in the Damon-Eshbach geometry by Brillouin light scattering spectroscopy reveals the drastic increase in the iDMI value with the increase in W thickness (tW). The maximum iDMI of −3.1 erg/cm2 is observed for tW = 0.24 nm, which is 10 times larger than for the quasi-symmetrical Ru/Co/Ru films. We demonstrate the evidence of the spontaneous field-driven nucleation of isolated skyrmions supported by micromagnetic simulations. Magnetic force microscopy measurements reveal the existence of sub-100-nm skyrmions in the z...

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.

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.

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 Bistability of the “Small Disk on Big Disk” Structure

On the basis of the micromagnetic simulations we reveal that in the small disk on big disk (d+D) nanostructure it is possible the sustained existence of a single-domain and vortex configurations of magnetization. The presence of the metastable state is possible due to the energy barrier, which is caused by magnetostatic interaction between disks. Switching between states can be performed by the external high frequency excitation. Magnetization switching of the small disk on big disk nanostructure is determined by the interaction of the vortex core in big disk with z-component of the magnetization of small disk.

Effect of the number of nanodisks in two-dimensional arrays on magnetization reversal processes

The magnetic properties of nanodisks packed into square arrays with various numbers of elements in the face have been studied. It has been shown that the vortex nucleation field oscillates with increasing number of nanodisks; the oscillation behavior depends on the nanodisk thickness. The synchronism of the vortex state formation varies with increasing number of nanodisks. The effect of the magnetostatic interaction of nanodisks on the critical fields of magnetization reversal has been estimated for the cases of vortex and single-domain states.