arXiv subjects

A. Kákay

Publications and source records attributed to A. Kákay.

3 recordsLinked to original sources

arXiv2025

Nonreciprocal spin-wave dispersion in magnetic bilayers

Nonreciprocal spin-wave propagation in bilayer ferromagnetic systems has attracted significant attention due to its potential to precisely quantify material parameters as well as for applications in magnonic logic and information processing. In this study we investigate the nonreciprocity of spin-wave dispersions in heterostructures consisting of two distinct ferromagnetic materials, focusing on the influence of saturation magnetization and thickness of the magnetic layers. We exploit Brillouin light scattering to confirm numerical calculations which are conducted with the finite element software TETRAX. An extensive numerical analysis reveals that the nonreciprocal behavior is strongly influenced by the changing material parameters, with asymmetry in the spin-wave propagation direction reaching several GHz under optimized conditions. Our findings demonstrate that tailoring the bilayer composition enables precise control over nonreciprocity, providing a pathway for engineering efficient unidirectional spin-wave devices. These results offer a deeper understanding of hybrid ferromagnetic systems and open avenues for designing advanced magnonic circuits.

cond-mat.mes-hall↗

arXiv2021

Self-stabilizing exchange-mediated spin transport

Long-range spin transport in magnetic systems can be achieved by means of exchange-mediated spin textures with robust topological winding -- a phenomenon referred to as spin superfluidity. Its experimental signatures have been discussed in antiferromagnets which are nearly free of dipolar interaction. However, in ferromagnets, which possess non-negligible dipole fields, realization of such spin transport has remained a challenge. Using micromagnetic simulations, we investigate coherent exchange-mediated spin transport in extended thin ferromagnetic films. We uncover a two-fluid state, in which the long-range spin transport by spin textures co-exists with spin waves, as well as a soliton-screened spin transport regime at high spin injection biases. Both states are associated with distinct spin texture reconstructions near the spin injection region and sustain spin transport over large distances.

cond-mat.other↗

arXiv2017

The complete micromagnetic characterization of asymmetrically sandwiched ferromagnetic films

The magnetic properties of ferromagnetic thin films down to the nanoscale are ruled by the exchange stiffness, anisotropies and the effects of magnetic fields. As surfaces break inversion symmetry, an additional effective chiral exchange is omnipresent in any magnetic nanostructure. These so-called Dzyaloshinskii-Moriya interactions (DMI) affect all inhomogeneous magnetic states either subtly or spectacularly. E.g., DMIs cause a chirality selection of the rotation sense and can fix the local rotation axis for the magnetization in domain walls (DW). But, they can stabilize also entirely different twisted magnetic structures. The chiral skyrmions a two-dimensional particle-like topological soliton is the ultimately smallest of these objects, which currently is targetted as a possible information carrier in novel spintronic devices. Observation and quantification of the chiral exchange effects provide for the salient point in understanding magnetic properties in ultrathin films and other nanostructures. An easy and reliable method to determine the DMI constant as materials parameter of asymmetric thin films is the crucial problem. Here, we put forth an experimental approach for the determination of the complete set of the micromagnetic parameters. Quasi-static Kerr microcopy observations of DW creep motion and equilibrium sizes of circular magnetic objects in combination with standard magnetometry are used to derive a consistent set of these materials parameters in polycrystalline ultrathin film systems, namely CrOx/Co/Pt stacks. The quantified micromagnetic model for these films identifies the circular magnetic objects, as seen by the optical microscopy, as ordinary bubble domains with homochiral walls. From micromagnetic calculations, the chiral skyrmions stabilized by the DMI in these films are shown to have diameters in the range 40-200nm, too small to be observed by optical microscopy.

cond-mat.mtrl-sci↗