Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session E22: Chiral Magnetism in Thin FilmsFocus
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Sponsoring Units: GMAG DMP Chair: Adam Ahmed, Ohio State Univ - Columbus Room: LACC 402A |
Tuesday, March 6, 2018 8:00AM - 8:12AM |
E22.00001: Chiral Magnetization States In Continuously Exchange Modulated Ferromagnets Brian Kirby, Lorenzo Fallarino, Patricia Riego, Brian Maranville, Casey Miller, Andreas Berger We have recently shown that compostional grading can be used to fabricate a ferromagnetic film with a continuous distribution of "local" Curie temperatures TC, corresponding to variations in exchange strength [1]. This led to interesting functionality, a quasi phase-bondary between strongly and weakly magnetized regions that can be continuously and reversibly moved along the growth axis. Here we consider the response of such an exchange graded structure to magnetic field. Since coercivity generally scales with T relative to TC, if the magnetic properties are sufficiently localized, the structure should reverse magnetization in a non-collinear fashion. We have fabricated Co1-xRux films with x continuously modulated in a triangular waveform along the growth direction. The TC of Co1-xRux scales with x, and we have used polarized neutron reflectometry (PNR) to show that the local TC is indeed modulated across distances as small as 4.9 nm. Field-dependent measurements at 300 K show that the sample magnetization of a 10 nm modulated sample does not reverse uniformly, instead forming a chiral state with the magnetizations of the highest local TC regions lagging those of the lowest local TC regions by approximately 20 degrees. |
Tuesday, March 6, 2018 8:12AM - 8:24AM |
E22.00002: Interlayer exchange coupling in Pt/Co/Ir multilayers films Sabit Karayev, Durga Khadka, Sunxiang Huang Magnetic Skyrmions with fascinating hurricane-like twisted spin textures have attracted intense attention recently because of their unusual physical properties and potential applications in new magnetic storage media and devices. In magnetic multilayer thin films with perpendicular magnetic anisotropy (PMA), the interfacial Dzyaloshinskii-Moriya interaction (iDMI) favors a faster rotation of the spins and can stabilize Skyrmions at room temperature [1]. |
Tuesday, March 6, 2018 8:24AM - 8:36AM |
E22.00003: Stray field signatures of Néel textured skyrmions in Ir/Fe/Co/Pt multilayer films Alon Yagil, Avior Almoalem, Anjan Soumyanarayanan, Anthony K. C. Tan, M. Raju, Christos Panagopoulos, Ophir Auslaender The development of technologically relevant skyrmions in multilayer films will require magnetic imaging methods sensitive to their spin structure, and translatable to device configurations. We present recent work [1] in which we use a multipole expansion to quantitatively describe the magnetic field of individual skyrmions in order to analyze low-temperature magnetic force microscopy (MFM) data. By using specific multipole signatures of skyrmions of different spin structure, we establish their Néel texture and helicity in a Ir/Fe/Co/Pt film at 5K. The demonstrated sensitivity to inhomogeneity provides a route for characterizing individual skyrmions in devices, and allows us to quantitatively analyze MFM images [2]. |
Tuesday, March 6, 2018 8:36AM - 8:48AM |
E22.00004: First-principles investigation of chiral magnetic structures in multilayers: {Rh|Co|Pt} and {Pd|Co|Pt} Hongying Jia, Bernd Zimmermann, Stefan Bluegel In the search and formation of chiral magnetic skyrmions in magnetic multilayers, the antisymmetric exchange interaction, known as Dzyaloshinskii-Moriya interaction (DMI), created at the surfaces and interfaces of metallic multilayers plays a determining role. |
Tuesday, March 6, 2018 8:48AM - 9:00AM |
E22.00005: ABSTRACT WITHDRAWN
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Tuesday, March 6, 2018 9:00AM - 9:12AM |
E22.00006: Directional growth of stripe domains in Co/Ni/Pt multilayers Jeffrey Brock, Pierre Vallobra, Rajasekhar Medapalli, Stephane Mangin, Eric Fullerton There has recently been strong interest in the control of DW motion using magnetic fields and electric current-related effects. The Dzyaloshinskii-Moriya interaction (DMI) due to inversion asymmetry at interfaces between magnetic materials and materials with large spin-orbit coupling can transform DWs from Bloch to chiral Néel, leading to asymmetric DW propagation. However, stripe domain growth in systems with DMI is not yet well understood. Here we present an experimental study of perpendicular anisotropy Ta(3 nm)/Pt(5 nm)/[Co(0.7 nm)/Ni(0.5 nm)/Pt(0.7 nm)]N (1 ≤ N ≤ 5) multilayers designed to have asymmetric Pt/Co and Ni/Pt interfaces. Kerr microscopy revealed that for N ≥ 3, magnetic reversal occurs via stripe domains. However, when a static in-plane magnetic field is applied, the domains grow in well-defined directions depending on the field strength. For low fields, the domains grow roughly perpendicular to the field. As the field increases, growth proceeds in the field direction. Above a critical field value, the propagation direction reverses, in a direction opposed to the field. Possible explanations as to the origin of these novel results will be provided. |
Tuesday, March 6, 2018 9:12AM - 9:24AM |
E22.00007: Dzyaloshinskii-Moriya interaction in Pt/Co/Ir and Pt/Co/Ru multilayers films Durga Khadka, Sabit Karayev, Sunxiang Huang Magnetic Skyrmions have attracted intense interest since they were discovered in 2009 in B20 magnets. In B20 magnets, in addition to symmetric Heisenberg exchange interaction, there is also a non-trivial anti-symmetric Dzyaloshinskii-Moriya interaction (DMI) which is key to realizing magnetic Skyrmions. In asymmetric magnetic multilayers, large interfacial DMI (iDMI) can be introduced to stabilize Skyrmions. The iDMI has displayed increasingly important roles in the modification of domain walls, stabilization of Skyrmions, and realization of new topological spin textures such as magnetic radial vortices. |
Tuesday, March 6, 2018 9:24AM - 9:36AM |
E22.00008: Interfacial Dzyaloshinskii-Moriya Interactions in Layered HM/GdCo/HM Samples Katherine Nygren, Robert Streubel, Kristen Buchanan Recent studies have shown that Dzyaloshinskii-Moriya interactions (DMI) play an important role in domain wall formation and motion as well as skyrmion stabilization. Quantitative measurements of the DMI for new material systems are needed to improve our understanding of how to optimize material parameters for applications such as spintronics. Current work establishes Brillouin light scattering (BLS) measurements of surface spin waves as one of the best available methods to measure the DMI. The DMI leads to a difference in the energy of surface spin waves with opposite propagation directions, which gives rise to a frequency shift that can be measured by BLS, a technique that is based on the inelastic scattering of light from spin waves. In this talk I will discuss how we have used BLS to measure the surface spin wave frequencies and compute the DMI of magnetic GdCo samples layered between heavy metals iridium (Ir) and platinum (Pt). By changing the angle of our sample with respect to the BLS probe laser we can select different wave vectors k. Fits to the frequency shift for the two spin wave directions as a function of k provide a quantitative measurement of the interfacial DMI for these samples. |
Tuesday, March 6, 2018 9:36AM - 9:48AM |
E22.00009: Dzyaloshinskii-Moriya interaction energy density for various metal insertion layer in Pt/Co/X/Pt (X=Al, Ti, Ta, W, Pt) by using Brillouin light scattering NAM-HUI KIM, Dae-Yun Kim, Yune-Seok Nam, Joo-Sung Kim, Hyeok-Cheol Choi, Min-ho Park, Yong-Keun Park, Sug-Bong Choe, Chun-Yeol You Interfacial Dzyaloshinskii-Moriya interaction (iDMI) is an important property for applying new type spintronics devices based on spin-orbit interaction phenomena. Especially, Brillouin light scattering (BLS) is powerful tools to directly observe the iDMI energy.1,2 In this study, we investigated the iDMI energy density for various atomic number using metal insertion layer by employing BLS measurement. All samples structures are Pt(2.5 nm)/Co(0.9 nm)/X(2.5 nm)/Pt(1.5 nm), X = (Al, Ti, Ta, W, Pt) which are deposited by magnetron sputtering. From systematic BLS measurement, we obtained asymmetric spin-wave propagation along to top (Stokes) and bottom (anti-Stokes) which can determine the iDMI energy density. Furthermore, the iDMI energy densities show consistent result with domain wall motion measurement considered the antisymmetric contribution such as chiral damping.3 |
Tuesday, March 6, 2018 9:48AM - 10:00AM |
E22.00010: Engineering the Dzyaloshinskii-Moriya interaction in MnxFe1-xGe thin films Emrah Turgut, Hanjong Paik, Kayla Nguyen, David Muller, Darrell Schlom, Gregory Fuchs Controlling chiral interactions in B20-hellimagnet systems is an exciting route to tailoring topological spin textures, e.g. Bloch skyrmions, in these systems. Forming MnxFe1-xGe alloys enable this control by varying x, which was previously studied using Lorentz transmission electron microscopy and neutron scattering studies on bulk MnxFe1-xGe crystals [1,2]. Thin film versions of this material enable spintronic devices that take advantage of non-collinear spin textures, however, the growth of MnxFe1-xGe compounds has been an outstanding challenge. Here we report the successful MBE growth and comprehensive characterization of epitaxial MnxFe1-xGe films. In addition, in concert with micromagnetic simulations, we use microwave absorption spectroscopy to quantify the Dzyaloshinskii-Moriya interaction. Our approach also tests the limits of micromagnetic computational treatment of a helimagnets in which the helical pitch is comparable to a lattice constant. |
Tuesday, March 6, 2018 10:00AM - 10:12AM |
E22.00011: Neutron study of in-plane skyrmions in MnSi thin films Simon Meynell, Murray Wilson, Kathryn Krycka, Brian Kirby, Helmut Fritzsche, Theodore Monchesky Magnetic skyrmions are vortex-like solitons that can arise in magnetic materials that have broken inversion symmetry. Micromagnetic calculations of thin epitaxial MnSi/Si films show that in-plane fields are capable of stabilizing skyrmions with their axis of symmetry pointing within the plane of the film. A polarized neutron reflectometry (PNR) study is presented that reveals the first direct evidence of this largely unexplored species of skyrmions. PNR measurements, which provide a depth profile of the magnetization, are interpreted with the aid of micromagnetic simulations. A potential well formed by the interaction with magnetic surface twists is found to play a key role in the confinement of these objects. |
Tuesday, March 6, 2018 10:12AM - 10:24AM |
E22.00012: 4-Dimensional Lorentz-STEM of Chiral FeGe Thin Films Kayla Nguyen, Emrah Turgut, Gregory Fuchs, David Muller Chiral magnets require extremely low current densities to manipulate their spins have been promising for applications in power-efficient memory devices. However, it is necessary to understand the behavior of chiral magnetic texture in thin-film materials with realistic disorder, such as B20 FeGe sputtered on Si. Lorentz TEM has been successful for high-resolution studies of chiral magnetic states in single-crystal B20 FeGe, imaging FeGe thin films in plan-view remains a challenge as grain sizes are comparable to those of magnetic textures. This makes distinguishing magnetic contrast from grain contrast challenging. We present a solution to this problem by collecting the full angular distribution of scattered electrons at each scan position with the electron microscopy pixel array detector developed at Cornell in Lorentz-STEM mode. We measure the chiral magnetic textures of B20 FeGe quantitatively, and directly separate grain structure contrast from magnetic contrast. We observe that the helical phases of B20 FeGe moves between grain boundaries and that magnetic skyrmions only form in free-standing FeGe films, illuminating the relationship between the FeGe chiral phases and lattice-induced strain. |
Tuesday, March 6, 2018 10:24AM - 10:36AM |
E22.00013: Non-Reciprocal Spin-Wave Emission from Topological Spin Textures Tobias Schneider, Volker Sluka, Attila Kakay, Markus Weigand, Tobias Warnatz, Roland Mattheis, Rodolfo Gallardo, Alejandro Roldán-Molina, Pedro Landeros, Vasyl Tyberkevych, Andrei Slavin, Artur Erbe, Alina DEAC, Jürgen Lindner, Jürgen Fassbender, Jörg Raabe, Sebastian Wintz Investigations of spin waves are of great interest for both fundamental science and applications. For the excitation of spin waves with short wavelengths, it was typically necessary to either use patterned transducers with sizes on the order of the desired wavelengths or to generate such spin waves parametrically. |
Tuesday, March 6, 2018 10:36AM - 10:48AM |
E22.00014: Using scanning plasmonic heating for nanoscale imaging of magnetization Jason Bartell, Jonathan Karsch, Colin Jermain, Jack Brangham, Fengyuan Yang, Daniel Ralph, Gregory Fuchs Advanced magnetic microscopies are key to advancing our understanding and application of novel magnetic phenomenon such as skyrmions, spinwaves, and domain walls. However, due to the diffraction-limit of light, achieving the 10-100 nanometer spatial resolution and 10 – 100 picosecond temporal resolution required to image these phenomenon is beyond the reach of table-top techniques. To break free of the far-field diffraction limit, we have been developing a near-field magnetic microscopy based on magneto-thermo interactions: the time-resolved anomalous Nernst effect and the time-resolved longitudinal spin Seebeck effect. This technique uses picosecond pulsed excitation of surface plasmon polaritons which are nanofocused to the apex of a scanning tip. The resulting near-field tip-sample interaction excites a nanoscale thermal gradient for magneto-thermal microscopy. We present sub-optical diffraction spatial resolution and picosecond temporal resolution in proof-of-concept experiments. Our results suggest a new approach to nanoscale spatiotemporal magnetic microscopy in an accessible, table-top form to aid in the development of high-speed magnetic devices. |
Tuesday, March 6, 2018 10:48AM - 11:00AM |
E22.00015: Current-induced magnetic domain wall motion in compensated ferrimagnet Saima Siddiqui, Jiahao Han, Joseph Finley, Caroline Ross, Luqiao Liu Antiferromagnets (AFMs) show promises compared to ferromagnets for spintronic devices due to their immunity to external magnetic fields and their ultra-fast dynamics. But the challenges in controlling and determining their magnetic state are limiting their technological applications. At the compensation point, the two antiparallel sub-lattices in a ferrimagnets have the same magnetic moment and the material is an AFM. Compensated ferrimagnets are expected to exhibit fast magnetic dynamics like an AFM and yet their magnetic state can be manipulated and detected like a ferromagnet, and therefore, have been pursued as a candidate system for fast spintronic applications. In this work, we provide the first experimental proof of current-induced fast domain wall (DW) motion in a compensated ferrimagnet. Using a magneto optic Kerr effect microscope, we determine the spin orbit torque-induced DW motion in Pt/Co1-xTbx with perpendicular magnetic anisotropy. We find that close to the angular momentum compensation, the DW mobility increases significantly, reflecting the fast magnetic dynamics in this regime. Moreover, by studying the dependence of the domain wall velocity with the in-plane field, we identify the structures of ferrimagnetic domain walls across the compensation points. |
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