Spintronics Theory Group

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  • Article

    Induced spin textures at 3d transition metal–topological insulator interfaces

    (American Physical Society (APS), 2020-06-25) Laref, Slimane; Ghosh, Sumit; Tsymbal, Evgeny Y.; Manchon, Aurelien; Physical Science and Engineering (PSE) Division; Material Science and Engineering Program; Applied Physics; Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588, USA; Aix-Marseille Univ, CNRS, CINaM, Marseille, France

    While some of the most elegant applications of topological insulators, such as the quantum anomalous Hall effect, require the preservation of Dirac surface states in the presence of time-reversal symmetry breaking, other phenomena such as spin-charge conversion rather rely on the ability for these surface states to imprint their spin texture on adjacent magnetic layers. In this Rapid Communication, we investigate the spin-momentum locking of the surface states of a wide range of monolayer transition metals (3d-TM) deposited on top of Bi2Se3 topological insulators using first-principles calculations. We find an anticorrelation between the magnetic moment of the 3d-TM and the magnitude of the spin-momentum locking induced by the Dirac surface states. While the magnetic moment is large in the first half of the 3d series, following Hund’s rule, the spin-momentum locking is maximum in the second half of the series. We explain this trend as arising from a compromise between intra-atomic magnetic exchange and covalent bonding between the 3d-TM overlayer and the Dirac surface states. As a result, while Cr and Mn overlayers can be used successfully for the observation of the quantum anomalous Hall effect or the realization of axion insulators, Co and Ni are substantially more efficient for spin-charge conversion effects, e.g., spin-orbit torque and charge pumping.

  • Article

    Spin-orbit coupling induced ultrahigh-harmonic generation from magnetic dynamics

    (American Physical Society (APS), 2022-05-31) Ly, Ousmane; Manchon, Aurelien; Applied Physics; Computer, Electrical and Mathematical Science and Engineering (CEMSE) Division; Material Science and Engineering Program; Physical Science and Engineering (PSE) Division; Spintronics Theory Group; Aix-Marseille Université, CNRS, CINaM, Marseille, France

    The generation of a nonlinear high-frequency response in solids from powerful optical pumps has gained momentum over the past decade. High-harmonic generation (HHG) in solids can be obtained from strong-field laser excitation, usually restricted to optical frequencies and limited both in amplitude and in harmonic order. Here, we demonstrate that high-harmonic emission can be achieved by exploiting conventional spin pumping, without the need for optical excitation. Considering a noncentrosymmetric (ferro- or antiferro-)magnet excited at a frequency ω, we demonstrate the emergence of HHG in two main regimes: (i) In the perturbative regime, where a weak spin-orbit interaction is considered, the carrier pumping features a number of harmonics with a cutoff order nmax<10. (ii) When the spin-orbit coupling strength is close to, or higher than, the s−d exchange energy, a strongly nonlinear regime resulting from resonantlike spin-flip scattering occurs leading to the emission of a large number of harmonics. This is in sharp contrast to conventional pumping, where the corresponding time-dependent currents simply oscillate with the frequency of the magnetic drive ω. Our proposal enables the enhancement of both spin and charge dynamics by orders of magnitude. This effect could be used to trigger high-frequency emission deep in the terahertz regime.

  • Article

    Unconventional spin pumping and magnetic damping in an insulating compensated ferrimagnet

    (Wiley, 2022-04-01) Li, Yan; Zheng, Dongxing; Fang, Bin; Liu, Chen; Zhang, Chenhui; Chen, Aitian; Ma, Yinchang; Shen, Ka; Liu, Haoliang; Manchon, Aurelien; Zhang, Xixiang; Applied Physics; Material Science and Engineering; Material Science and Engineering Program; Physical Science and Engineering (PSE) Division; Spintronics Theory Group; The Center for Advanced Quantum Studies and Department of Physics Beijing Normal University Beijing 100875 China; School of Science, Harbin Institute of Technology Shenzhen 518055 China; Aix-Marseille Université CNRS, CINaM Marseille France

    Recently, the interest in spin pumping has escalated from ferromagnets into antiferromagnetic systems, potentially enabling fundamental physics and magnonic applications. Compensated ferrimagnets are considered alternative platforms for bridging ferro- and antiferromagnets, but their spin pumping and the associated magnetic damping have been largely overlooked so far despite their seminal importance for magnonics. Herein, we report an unconventional spin pumping together with magnetic damping in an insulating compensated ferrimagnet Gd3Fe5O12. Remarkably, we unambiguously identified the divergence of the nonlocal effective magnetic damping induced by spin pumping close to the compensation temperature in Gd3Fe5O12/Cu/Pt heterostructures. Furthermore, the coherent and incoherent spin currents, generated by spin pumping and spin Seebeck effect respectively, undergo a distinct direction change with the variation of temperature. The physical mechanisms underlying these observations are self-consistently clarified by the ferrimagnetic counterpart of spin pumping and the handedness-related spin-wave spectra. Our findings broaden the conventional paradigm of the ferromagnetic spin pumping model and open new opportunities for exploring the ferrimagnetic magnonic devices.

  • Article

    Competition between chiral energy and chiral damping in the asymmetric expansion of magnetic bubbles

    (ACS Applied Electronic Materials., 2021-10) Ganguly, Arnab; Zhang, Senfu; Mibhaimiron, Loan; Kosel, Jürgen; Zhang, Xixiang; Manchon, Aurelien; Singh, Nirpendra; Anjum, Dalaver; Das, Gobind; Computer, Electrical and Mathematical Science and Engineering (CEMSE) Division; Electrical and Computer Engineering Program; Material Science and Engineering Program; Physical Science and Engineering (PSE) Division; Sensing, Magnetism and Microsystems Lab; Spintronics Theory Group; Department of Physics, Khalifa University, Abu Dhabi 12788, United Arab Emirates.; CNRS, SPINTEC, 38000 Grenoble, France; Sensor Systems Division, Silicon Austria Labs, 9524 Villach, Austria; CINaM, Aix-Marseille University, CNRS, 13288 Marseille, France; Center for Catalysis and Separations, Khalifa University, Abu Dhabi 127788, UAE

    Magnetic chirality is an important knob in spintronics and can be engineered through structural symmetry breaking of magnetic thin film multilayers. The dynamics of chiral domain walls is determined by the cooperation of chiral contributions in the magnetic energy functional as well as in the dissipation tensor which need to be better controlled for the sake of the device applications. In this work, we performed a systematic study of magnetic field-induced magnetic bubble expansion in structural inversion asymmetric multilayers with different Pt thicknesses using polar magneto-optical Kerr microscopy. Asymmetric expansion of magnetic bubble is investigated in the creep regime as a function of in-plane and out-of-plane magnetic fields. The results reveal the competition between two key mechanisms governing the asymmetry in the field-driven domain wall expansion, namely the Dzyaloshinskii-Moriya interaction and the chiral magnetic damping. The interplay between these two effects leads to the seemingly counterintuitive experimental signature, depending on the strength of the external magnetic field. The effective control on the bubble asymmetry expansion can be of great importance for future memory and multiplexer-based applications.

  • Article

    Skyrmion battery effect via inhomogeneous magnetic anisotropy

    (AIP Publishing, 2021-04-14) Hao, Xiawei; Zhuo, Fengjun; Manchon, Aurelien; Wang, Xiaolin; Li, Hang; Cheng, Zhenxiang; King Abdullah University of Science and Technology (KAUST); Material Science and Engineering Program; Physical Science and Engineering (PSE) Division; Spintronics Theory Group; School of Physics and Electronics, Henan University, Kaifeng 475004, China; Interdisciplinary Nanoscience Center of Marseille (CINaM), Aix-Marseille University, Marseille 13288, France; Institute for Superconducting and Electronic Materials, Australian Institute of Innovative Materials, University of Wollongong, Innovation Campus, Squires Way, North Wollongong, NSW 2500, Australia

    Magnetic skyrmions are considered a promising candidate for the next-generation information processing technology. Being topologically robust, magnetic skyrmions are swirling spin textures that can be used in a broad range of applications from memory devices and logic circuits to neuromorphic computing. In a magnetic medium lacking inversion symmetry, magnetic skyrmion arises as a result of the interplay among magnetic exchange interaction, Dzyaloshinskii-Moriya interaction, and magnetic anisotropy. Instrumental to the integrated skyrmion-based applications are the creation and manipulation of magnetic skyrmions at a designated location, absent any need of a magnetic field. In this paper, we propose a generic design strategy to achieve that goal and a model system to demonstrate its feasibility. By implementing a disk-shaped thin film heterostructure with an inhomogeneous perpendicular magnetic anisotropy, stable sub-100-nm size skyrmions can be generated without magnetic field. This structure can be etched out via, for example, focused ion beam microscope. Using micromagnetic simulation, we show that such heterostructure not only stabilizes the edge spins of the skyrmion but also protects its rotation symmetry. Furthermore, we may switch the spin texture between skyrmionic and vortex-like ones by tuning the slope of perpendicular anisotropy using a bias voltage. When embedded into a magnetic conductor and under a spin polarized current, such heterostructure emits skyrmions continuously and may function as a skyrmion source. This unique phenomenon is dubbed a skyrmion battery effect. Our proposal may open a novel venue for the realization of all-electric skyrmion-based devices.