Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session A54: Skyrmions and Chiral Spin Textures in Thin Films and Multilayers |
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Sponsoring Units: GMAG Chair: Mi-Young Im, Lawrence Berkeley National Laboratory Room: Room 306 |
Monday, March 6, 2023 8:00AM - 8:12AM |
A54.00001: Observation of room-temperature magnetic skyrmions in Pt/Co/Cu multilayers Ziling Li, Shuyu Cheng, Nuria Bagues Salguero, Camelia Selcu, Binbin Wang, Shekhar Das, P Chris Hammel, David W McComb, Roland K Kawakami Magnetic skyrmions are a promising candidate for high-density and energy-efficient information storage and processing. Magnetic multilayers systems Pt/Co/X (X= metallic element) provide an ideal platform to study skyrmions due to the rich tunability of magnetic properties. Here we report observation of room-temperature skyrmions in epitaxial grown [Pt/Co/Cu]5 multilayers on insulating substrates. The magnetic properties were characterized by magneto-optical Kerr effect (MOKE) and SQUID magnetometer measurements. The skyrmions were confirmed by Lorentz transmission electron microscopy (LTEM) and magnetic force microscope (MFM). Furthermore, by tunning Co layer thickness and periods number of multilayers, we are able to modify magnetic properties as well as skyrmions in multilayers. |
Monday, March 6, 2023 8:12AM - 8:24AM |
A54.00002: Room-temperature chirality switching in a helimagnetic thin film Hidetoshi Masuda, Takeshi Seki, Yoichi Nii, Hiroto Masuda, Koki Takanashi, Yoshinori Onose Helimagnetic structures, in which the magnetic moments are spirally ordered, host an internal degree of freedom called chirality (or helicity) corresponding to the handedness of the helix. It hosts an internal degree of freedom called chirality (or helicity) corresponding to the handedness of the helix. The chirality seems quite robust against disturbances and is therefore promising for next-generation magnetic memory. While the chirality control was recently achieved by the magnetic field sweep with the application of an electric current at low temperature in a conducting helimagnet[1], problems such as low working temperature and cumbersome control sequence have to be solved in practical applications. Another issue is the thin film fabrication that enables the development of spintronic devices based on helimagnets. Here we show chirality switching by electric current pulses at room temperature in a thin-film MnAu2 helimagnetic conductor[2]. The result demonstrates the feasibility of helimagnet-based spintronics that can overcome all the above problems. |
Monday, March 6, 2023 8:24AM - 8:36AM |
A54.00003: Stoichiometric variations of fluctuation heterogeneity of stripe domains in amorphous Fe-Ge thin films ARNAB SINGH, Emily M Hollingworth, Sophie A Morley, Xiaoqian M Chen, Ahmad Us Saleheen, Ryan Tumbleson, Margaret R McCarter, Peter J Fischer, Frances Hellman, Stephen D Kevan, Sujoy Roy Magnetic thin-films provide a unique system to study the evolution of exotic spin-textures which are fundamentally intriguing and potentially promising for spintronics application. A key question to address is how symmetric and anti-symmetric exchange coupling between atomic spins modulate the nature of fluctuations as the system approaches phase transition. In amorphous Fe-Ge thin films by controlling the Fe concentration one can tune the magnitude of the symmetric Heisenberg exchange and randomness of anti-symmetric Dzyaloshinskii-Moriya interaction (DMI) respectively. In this work we performed soft x-ray photon correlation spectroscopy (XPCS) measurements to probe the nanoscale magnetic fluctuations of stripe domains in amorphous FexGe1−x thin films for x=0.51, 0.52 and 0.53. The fluctuations were found to be length-scale specific heterogeneous; starting over a small fraction of the domains well below TC and the fluctuation amplitude gradually grows into a collective fluctuation encompassing the entire film as TC was approached. We also observed that stoichiometry has a profound effect on the spectrum of thermal fluctuations which forms the basis of phase transition pathway. Specifically, for the same reduced temperature, we observed enhanced thermally activated fluctuations with decreasing Fe concentration. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A54.00004: Effects of Disorder on the Skyrmion Phase in FeGe Thin Films Michael B Venuti, Portia J Allen, Eric J Lang, Hanjong Paik, Khalid Hattar, Tzu-Ming Lu, Serena M Eley Magnetic skyrmions are nanoscale whirlpools of magnetic moments that arise certain magnetic materials and are potentially useful as information carriers in next-generation low-energy spintronic devices. To exploit skyrmions in spintronics, we must be able to controllably manipulate them, which necessitates understanding how to create, annihilate, and move them. It also requires understanding how the skyrmion lattice is affected by disorder, dictating how skyrmions will either maneuver around or be pinned by energy barriers within the material's disorder landscape. Here, we report on the effects of point disorder on the skyrmion phase in epitaxial FeGe thin films. To tune defect densities, we irradiate the films with 2.8 MeV Au ions, varying the dose to control the densities of induced vacancies. We then conduct electrical transport measurements to identify magnetic phase changes through changes in the topological Hall resistivity, perform complimentary MFM measurements to image the magnetic textures, and compare the subsequently constructed field-temperature phase diagrams of the irradiated and pristine samples to systematically observe disorder-induced changes in the skyrmion lattice phase. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A54.00005: 3D topological spin textures in magnetic multilayers David Raftrey, Peter J Fischer, Simone Finizio, Jörg Raabe, Tiffany S Santos, Scott Dhuey Magnetic Skyrmions are topological spin textures that are scientifically interesting and hold promise for low-power information technology devices. Although their properties are well understood in the framework of 2D systems, in real materials the extension of skyrmions into the 3rd dimension cannot be neglected and has opened a plethora of novel topological spin textures. Among those spin textures are skyrmion tubes, chiral bobbes, magnetic cocoons, torons and also magnetic Hopfions [1]. Target Skyrmions [2] have been predicted [3] to be precursors of magnetic Hopfions in magnetic multilayers and have recently been experimentally verified using complementary surface and bulk sensitive magnetic soft x-ray microscopies [4]. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A54.00006: Anomalous Hall Effect in Epitaxial Thin Films of the Hexagonal Heusler MnPtGa Noncollinear Hard Magnet Edouard Lesne, Rebeca Ibarra, Bushra Sabir, Bachir Ouladiaff, Ketty Beauvois, Alexandr S Sukhanov, Rafal Wawrzynczak, Walter Schnelle, Anton Devishvili, Dmytro S Inosov, Jacob Gayles, Claudia Felser, Anastasios Markou Magnetic systems exhibiting spin-canted states have garnered much attention recently for their promising rich exotic properties driven by the real-space spin textures and competing magnetic orders. We report here on the magnetic groundtstate and Berry curvature-driven intrinsic anomalous Hall effect (AHE) of hexagonal Heusler MnPtGa epitaxial thin films. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A54.00007: Controlling interfacial Dzyaloshinskii-Moriya interaction and magnetic skyrmions in Ru/Pd/Co/Ni based heterostructure Md Mahadi Rajib, Dhritiman Bhattacharya, Christopher Jensen, Gong Chen, Jayasimha Atulasimha, Kai Liu Dzyaloshinskii-Moriya interaction (DMI) leads to the formation of non-trivial spin textures such as magnetic skyrmions which are being investigated heavily to be incorporated in future nanomagnetic memory and computing devices. Thus, efficient ways of controlling DMI are needed to stabilize and manipulate skyrmions in practical devices. DMI at heavy metal/ferromagnet interface vary widely in size and sign, presenting a possibility to fabricate multilayer systems with precise DMI values by designing different interfaces. Here we report controlling DMI in multilayer heterostructures of (Co/Ni)n/Pd(t)/Ru with varying Pd layer thicknesses (t). We employed magneto-optic Kerr effect (MOKE) imaging to capture asymmetric bubble domain expansion under different in-plane magnetic fields and estimated DMI in these samples. As DMI of opposite signs are produced by Co/Pd [1] and Co/Ru [2], the DMI was found to be tunable, e.g., from clearly Pd-like (i.e. left-handed) to essentially zero with a small reduction of Pd thickness. Furthermore, skyrmions are observed in these samples, whose size and density are explored under different interface characteristics. These results demonstrate a new interface design to regulate DMI and consequently skyrmions. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A54.00008: Elliptical skyrmions: Theory and nucleation by a magnetic tip in an antiskyrmion-hosting material Daniel Capic Motivated by experimental findings in Jena et al. [1] and Peng et al. [2], in [3] we find an elliptical skyrmion can be nucleated in a material with a Dzyaloshinskii–Moriya interaction (DMI) that supports antiskyrmions. The DMI favors the elongation of the skyrmion along a given direction so that it is characterized by two size parameters. We derive analytical properties of the elliptical skyrmion using the Belavin–Polyakov (BP) pure exchange model. We show that the DMI which typically favors isotropic skyrmions or antiskyrmions, respectively, can also support elliptical antiskyrmions or skyrmions, respectively. Using the real material parameters extracted from Jena et al. [1] and including all relevant interactions, numerical computations indicate that the elliptical skyrmion can be nucleated from the stripe or labyrinth domain state by a magnetic force microscope tip in a thin film with a DMI favoring antiskyrmions that consists of at least a few atomic layers. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A54.00009: Skyrmion formation in Ni-based Janus dihalide monolayers: Interplay between magnetic frustration and Dzyaloshinskii-Moriya interaction Jyotirish Das, Taylan Gorkan, Jesse Kapeghian, Muhammad Akram, Johannes V barth, Sefaattin Tongay, Ethem Aktürk, Onur Erten, Antia S Botana I will present a comprehensive theory of the magnetic phases in monolayer nickel-based Janus dihalides (NiIBr,NiICl,NiBrCl) by using first principle calculations and atomistic simulations. The parameters of the interacting spin Hamiltonian extracted from ab-initio calculations show that nickel-dihalide Janus monolayers exhibit varying degrees of magnetic frustration together with a large Dzyaloshinskii_Moriya interaction due to their inherent inversion breaking symmetry. The atomistic simulations reveal a delicate interplay between these two competing magnetic interactions in giving rise to skyrmion formation. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A54.00010: Stabilization of chiral Bloch skyrmions due to interfacial DMI and asymmetric vertical Bloch line evolution. Michael D Kitcher, Nisrit Pandey, Vincent Sokalski, Marc De Graef We show that Bloch chirality preference in magnetic domain walls and skyrmions can originate from the interplay between an interfacial Dzyaloshinskii–Moriya interaction (iDMI) and a perpendicular magnetic field. This is starkly evident in Pt/Ni/Co thin films with a DMI lower than the critical strength required to form purely Néel walls and skyrmions. Imaging of skyrmion arrays via Lorentz transmission electron microscopy reveals an unmistakable preference for one Bloch chirality which switches. Analytical and micromagnetic modelling show that while conventional iDMI does not break energetic symmetry of the two Bloch chiralities, the energy barrier to switch between two Bloch chiralties becomes asymmetric; an out-of-plane field can thus stabilize a single Bloch chirality both at steady state and upon removing the field. We also demonstrate that the growth of favorable 'worm' domains—precursors to the observed skyrmions—is mediated by vertical Bloch line (VBL) evolution pursuant to the signs of the DMI vector and the applied field. As our modelling and imaging reveal, iDMI breaks the degeneracy in the nucleation energy, free energy, and velocity of VBLs, while the applied field dictates that their asymmetric nucleation and movement favor the same Bloch chirality that is preferred in their absence. Beyond elucidating previously unexplained correlations between preferential Bloch chirality and iDMI, this study offers promising pathways to explore memory devices based on Bloch chirality switching. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A54.00011: Micromagnetic simulation of magnetic switching behavior of permalloy nanocap thin films Jiyeong Gu, Angel Gomez, Epi Garcia, Jose Chavez Magnetic hysteresis loops of Permalloy nanocap thin films fabricated on top of nanospheres are simulated using MuMax3, a micromagnetic simulation program, to study the magnetic switching behavior of curved magnetic thin films. Four different shapes are introduced to construct a single nanocap used in the simulation. For a given shape, various thicknesses of the nanocap with a fixed diameter of nanosphere, and various diameters of nanosphere with a fixed thickness of the layer were studied in the simulation. Simulation results were compared to investigate how the thickness (t), diameter (d), and the ratio of t/d will change the magnetic switching behavior of nanocap thin films. Hysteresis loops showed more drastic change with varying the thickness compared to the diameter. Based on the comparison among the different shapes the one showing the hysteresis loops with well-defined coercivity was chosen and further simulations on extended shapes were made. Seven nanocaps in a hexagonal pattern were simulated to observe how the interaction among the nanocaps changes the magnetic switching behavior of the system. The formation of magnetic vortices was more likely to happen in seven nanocaps. The orientation of the vortices on the top and bottom rows were influenced by the direction of the magnetic moment of the middle row in the hexagonal pattern. Also, there were two different chirality were observed in the magnetic vortices. To remove the edge effect, seven nanocaps were extended to a grid pattern that maintains the self-assembled pattern with periodic boundary conditions. It was found that magnetic vortices were formed when there was interaction among the nanocaps and neighboring vortices were interacting along the hysteresis loop. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A54.00012: Surface acoustic waves and skyrmions Anil Adhikari, Shireen Adenwalla We investigate the effect of high-frequency surface acoustic waves (SAW) on a variety of magnetic textures using polar magneto-optical Kerr microscopy in 128º Y cut LiNbO3/Ta(3nm)/Pt(3nm)CoFeB(0.4nm)Pt(2nm). The as-deposited samples are in a single-domain state that remains impervious to magnetic field configurations. Low-temperature annealing results in multi-domain states and a subsequent field sweep results in the nucleation of bubbles. The application of SAW rapidly increases the density of bubbles. We report on SAW-driven magnetic switching in the single-domain state and the SAW-driven dynamics of bubble domains in the multi-domain state. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A54.00013: S-shaped Magnetic Configurational States in Individual Square Permalloy Particles Barry N Costanzi Zero-field magnetic configurations on the mesoscale depend significantly on particle size and shape as the exchange and magnetostatic energies become comparable. This results in systems that are neither single- nor multi-domain, but in a variety of possible configurational states, often with non-uniform magnetization but a net moment. As candidates for non-volatile memory and magnetic logic devices, understanding the allowed states and energies of these types of structures is paramount, while also providing a lens into the governing fundamental physics. Previous work has focused on arrays of particles, but this can obfuscate particular details of individuals. |
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