Nanomagnetismus a spintronika
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- ItemZero-field spin wave turns(AIP Publishing, 2024-03-11) Klíma, Jan; Wojewoda, Ondřej; Roučka, Václav; Molnár, Tomáš; Holobrádek, Jakub; Urbánek, MichalSpin-wave computing, a potential successor to CMOS-based technologies, relies on the efficient manipulation of spin waves for information processing. While basic logic devices such as magnon transistors, gates, and adders have been experimentally demonstrated, the challenge for complex magnonic circuits lies in steering spin waves through sharp turns. In this study, we demonstrate with micromagnetic simulations and Brillouin light scattering microscopy experiments, that dipolar spin waves can propagate through 90 degrees turns without distortion. The key lies in carefully designed in-plane magnetization landscapes, addressing challenges posed by anisotropic dispersion. The experimental realization of the required magnetization landscape is enabled by spatial manipulation of the uniaxial anisotropy using corrugated magnonic waveguides. The findings presented in this work should be considered in any magnonic circuit design dealing with anisotropic dispersion and spin wave turns.
- ItemPreserving Metamagnetism in Self-Assembled FeRh Nanomagnets(AMER CHEMICAL SOC, 2023-02-15) Motyčková, Lucie; Arregi Uribeetxebarria, Jon Ander; Staňo, Michal; Průša, Stanislav; Částková, Klára; Uhlíř, VojtěchPreparing and exploiting phase-change materials in the nanoscale form is an ongoing challenge for advanced material research. A common lasting obstacle is preserving the desired functionality present in the bulk form. Here, we present self-assembly routes of metamagnetic FeRh nanoislands with tunable sizes and shapes. While the phase transition between antiferro-magnetic and ferromagnetic orders is largely suppressed in nanoislands formed on oxide substrates via thermodynamic nucleation, we find that nanomagnet arrays formed through solid-state dewetting keep their metamagnetic character. This behavior is strongly dependent on the resulting crystal faceting of the nanoislands, which is characteristic of each assembly route. Comparing the calculated surface energies for each magnetic phase of the nanoislands reveals that metamagnetism can be suppressed or allowed by specific geometrical configurations of the facets. Furthermore, we find that spatial confinement leads to very pronounced supercooling and the absence of phase separation in the nanoislands. Finally, the supported nanomagnets are chemically etched away from the substrates to inspect the phase transition properties of self-standing nanoparticles. We demonstrate that solid-state dewetting is a feasible and scalable way to obtain supported and free-standing FeRh nanomagnets with preserved metamagnetism.
- ItemControl of domain structure and magnetization reversal in thick Co/Pt multilayers(American Physical Society, 2019-01-25) Fallarino, Lorenzo; Oelschlägel, Antje; Arregi Uribeetxebarria, Jon Ander; Bashkatov, Aleksander; Samad, Fabian; Böhm, B.; Chesnel, Karine; Hellwig, OlavWe present a study of the magnetic properties of [Co(3.0 nm)/Pt(0.6nm)]N multilayers as a function of Co/Pt bilayer repetitions N. Magnetometry investigation reveals that samples with N 15 exhibit two characteristic magnetization reversal mechanisms, giving rise to two different morphologies of the remanent domain pattern. For applied magnetic field angles near the in-plane field orientation, the magnetization reversal proceeds via a spontaneous instability of the uniform magnetic state resulting in perpendicular stripe domains. Conversely, for field angles close to the out-of-plane orientation, the reversal occurs via domain nucleation and propagation leading to a mazelike domain pattern at remanence. Our measurements further enable the characterization of the N-dependent energy balance between the magnetic anisotropy and magnetostatic energy contributions, revealing a gradual disappearance of the domain nucleation process during magnetization reversal for N < 14. This leads to the exclusive occurrence of an instability reversal mechanism for all field orientations as well as alignedlike stripe domains at remanence. Furthermore, a detailed study of the influence of the magnetic history allows the determination of a range of material properties and magnetic field strengths, where a lattice of bubble domains with remarkably high density is stabilized. These modulations of the ferromagnetic order parameter are found to strongly depend on N, in terms of center-to-center bubble distance as well as of bubble diameter. Moreover, such Co/Pt multilayers could be utilized to engineer field reconfigurable bubble domain lattices, which resemble magnonic crystals.
- ItemDimensional crossover of microscopic magnetic metasurfaces for magnetic field amplification(AIP Publishing, 2024-07-01) Lejeune, Nicolas; Fourneau, Emile; Barrera, Aleix; Morris, Oliver; Leonard, Oscar; Arregi Uribeetxebarria, Jon Ander; Navau, Carles; Uhlíř, Vojtěch; Bending, Simon; Palau, Anna; Silhanek, Alejandro VladimiroTransformation optics applied to low frequency magnetic systems have been recently implemented to design magnetic field concentrators and cloaks with superior performance. Although this achievement has been amply demonstrated theoretically and experimentally in bulk 3D macrostructures, the performance of these devices at low dimensions remains an open question. In this work, we numerically investigate the non-monotonic evolution of the gain of a magnetic metamaterial field concentrator as the axial dimension is progressively shrunk. In particular, we show that in planar structures, the role played by the diamagnetic components becomes negligible, whereas the paramagnetic elements increase their magnetic field channeling efficiency. This is further demonstrated experimentally by tracking the gain of superconductor-ferromagnet concentrators through the superconducting transition. Interestingly, for thicknesses where the diamagnetic petals play an important role in the concentration gain, they also help to reduce the stray field of the concentrator, thus limiting the perturbation of the external field (invisibility). Our findings establish a roadmap and set clear geometrical limits for designing low dimensional magnetic field concentrators.
- ItemResearch Update: Focused ion beam direct writing of magnetic patterns with controlled structural and magnetic properties(AIP Publishing, 2018-06-01) Urbánek, Michal; Flajšman, Lukáš; Křižáková, Viola; Gloss, Jonáš; Horký, Michal; Schmid, Michael; Varga, PeterFocused ion beam irradiation of metastable Fe78Ni22 thin films grown on Cu(100) substrates is used to create ferromagnetic, body-centered cubic patterns embedded into paramagnetic, face-centered-cubic surrounding. The structural and magnetic phase transformation can be controlled by varying parameters of the transforming gallium ion beam. The focused ion beam parameters such as the ion dose, number of scans, and scanning direction can be used not only to control a degree of transformation but also to change the otherwise four-fold in-plane magnetic anisotropy into the uniaxial anisotropy along a specific crystallographic direction. This change is associated with a preferred growth of specific crystallographic domains. The possibility to create magnetic patterns with continuous magnetization transitions and at the same time to create patterns with periodical changes in magnetic anisotropy makes this system an ideal candidate for rapid prototyping of a large variety of nanostructured samples. Namely, spin-wave waveguides and magnonic crystals can be easily combined into complex devices in a single fabrication step