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Register a new userCreation of a Chiral Bobber Lattice in Helimagnet-Multilayer Heterostructures
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A chiral bobber is a localized three-dimensional magnetization configuration, terminated by a singularity. Chiral bobbers coexist with magnetic skyrmions in chiral magnets, lending themselves to new types of skyrmion-complementary bits of information. However, the on-demand creation of bobbers, as well as their direct observation remained elusive. Here, we introduce a new mechanism for creating a stable chiral bobber lattice state via the proximity of two skyrmion species with comparable size. This effect is experimentally demonstrated in a Cu$_2$OSeO$_3$/[Ta/CoFeB/MgO]$_4$ heterostructure in which an exotic bobber lattice state emerges in the phase diagram of Cu$_2$OSeO$_3$. To unambiguously reveal the existence of the chiral bobber lattice state, we have developed a novel characterization technique, magnetic truncation rod analysis, which is based on resonant elastic x-ray scattering.
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Magnetic-field effect on the magnetic and electric properties in a chiral polar ordered corundum Ni$_2$InSbO$_6$ has been investigated. Single-crystal soft x-ray and neutron diffraction measurements confirm long-wavelength magnetic modulation. The modulation direction tends to align along the magnetic field applied perpendicular to the polar axis, suggesting that the nearly proper-screw type helicoid should be formed below 77,K. The application of a high magnetic field causes a metamagnetic transition. In a magnetic field applied perpendicular to the polar axis, a helix-to-canted antiferromagnetic transition takes place through the intermediate soliton lattice type state. On the other hand, a magnetic field applied along the polar axis induces a first-order metamagnetic transition. These metamagnetic transitions accompany a change in the electric polarization along the polar axis.
The chiral helimagnet, $Cr_{1/3}NbS_{2}$, hosts exotic spin textures, whose influence on the magneto-transport properties, make this material an ideal candidate for future spintronic applications. To date, the interplay between macroscopic magnetic and transport degrees of freedom is believed to result from a reduction in carrier scattering following spin order. Here, we present electronic structure measurements through the helimagnetic transition temperature, $T_{C}$ that challenges this view by showing a Fermi surface comprised of strongly hybridized Nb- and Cr- derived electronic states, and spectral weight in proximity to the Fermi level to anomalously increases as temperature is lowered below $T_{C}$. These findings are rationalized on the basis of first principle, density functional theory calculations, which reveal a large nearest-neighbor exchange energy, suggesting the interaction between local spin moments and hybridized Nb- and Cr- derived itinerant states to go beyond the perturbative interaction of Ruderman-Kittel-Kasuya-Yosida, suggesting instead a mechanism rooted in a Hunds exchange interaction.
Competing interactions produce finite-size textures in myriad condensed matter systems, typically forming elongated stripe or round bubble domains. Transitions between stripe and bubble phases, driven by field or temperature, are expected to be reversible in nature. Here we report on the distinct character of the analogous transition for nanoscale spin textures in chiral Co/Pt-based multilayer films, known to host N{e}el skyrmions, using microscopy, magnetometry, and micromagnetic simulations. Upon increasing field, individual stripes fission into multiple skyrmions, and this transition exhibits a macroscopic signature of irreversibility. Crucially, upon field reversal, the skyrmions do not fuse back into stripes, with many skyrmions retaining their morphology down to zero field. Both the macroscopic irreversibility and the microscopic zero-field skyrmion density are governed by the thermodynamic material parameter determining chiral domain stability. These results establish the thermodynamic and microscopic framework underlying ambient skyrmion generation and stability in chiral multilayer films and provide immediate directions for their functionalization in devices.
We examine the atomic intermixing phenomenon in three distinct amorphous CoB-based multilayer thin film platforms - Pt/CoB/Ir, Ir/CoB/Pt and Pt/CoB/MgO - which are shown to stabilise room-temperature chiral magnetic textures. Intermixing occurs predominantly between adjacent metallic layers. Notably, it is stack-order dependent, and particularly extensive when Ir sits atop CoB. Intermixing induced variations in magnetic properties are ascribed to the formation of magnetic dead layer arising from CoIr alloying in the metallic stacks. It also produces systematic variations in saturation magnetization, by as much as 30%, across stacks. Crucially, the resulting crossover CoB thickness for the transition from perpendicular to in-plane magnetic anisotropy differs by more than 2x across the stacks. Finally, with thermal annealing treatment over moderate temperatures of 150-300 degree Celsius, the magnetic anisotropy increases monotonically across all stacks, coupled with discernibly larger Hc for the metallic stacks. These are attributed to thermally induced CoPt alloying and MgO crystallization in the metallic and oxide stacks, respectively. Remarkably, the CoB in the Pt/CoB/MgO stacks retains its amorphous nature after annealing. Our results set the stage for harnessing the collective attributes of amorphous CoB-based material platforms and associated annealing processes for modulating magnetic interactions, enabling the tuning of chiral magnetic texture properties in ambient conditions.
In spite of both technical and fundamental importance, reversal of a macroscopic magnetization by an electric field (E) has been limitedly realized and remains as one of great challenges. Here, we report the realization of modulation and reversal of large magnetization (M) by E in a multiferroic crystal Ba0.5Sr1.5Zn2(Fe0.92Al0.08)12O22, in which a transverse conical spin state exhibits a remanent M and electric polarization below ~150 K. Upon sweeping E between +- 2 MV/m, M is quasi-linearly varied between +- 2 {mu}B/f.u., resulting in the M reversal. Moreover, the remanent M shows non-volatile changes of {Delta}M = +- 0.15 {mu}B/f.u., depending on the history of the applied electric fields. The large modulation and the non-volatile two-states of M at zero magnetic field are observable up to ~150 K where the transverse conical spin state is stabilized. Nuclear magnetic resonance measurements provide microscopic evidences that the electric field and the magnetic field play an equivalent role, rendering the volume of magnetic domains change accompanied by the domain wall motion. The present findings point to a new pathway for realizing the large magnetization reversal by electric fields at fairly high temperatures.
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