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 Q57: Magnonics II |
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Sponsoring Units: GMAG Chair: Florian Dirnberger, Technical University of Dresden Room: Room 303 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q57.00001: Single- and multi-magnon dynamics in antiferromagnetic α-Fe2O3 thin films Jiemin Li, Yanhong Gu, Yoshihiro Takahashi, Keisuke Higashi, Taehun Kim, Yang Cheng, Fengyuan Yang, Jan Kunes, Jonathan Pelliciari, Atsushi Hariki, Valentina Bisogni Understanding the spin dynamics in antiferromagnetic (AFM) thin films is fundamental for designing novel devices based on AFM magnon transport. Here, we study the magnon dynamics in thin films of AFM S = 5/2 α-Fe2O3 by combining resonant inelastic x-ray scattering, Anderson impurity model plus dynamical mean-field theory, and the Heisenberg spin model. Below 100 meV, we observe the thickness-independent (down to 15 nm) acoustic single magnon mode. At higher energies (∼ 100−500 meV), an unexpected sequence of equally spaced, optical modes is resolved and ascribed to ?Sz = 1, 2, 3, 4, and 5 magnetic excitations corresponding to multiple, non-interacting magnons. Our study unveils the energy, character, and momentum-dependence of single- and multimagnons in α-Fe2O3 thin films, with impact on AFM magnon transport and its related phenomena. On a broader perspective, we generalize the use of L-edge RIXS as a multi-spin excitation probe up to ?Sz = 2S. Our analysis identifies the spin-orbital mixing in the valence shell as the key element for accessing excitations beyond ?Sz = 1, and up to e.g. ?Sz = 5. At the same time, we elucidate the novel origin of the spin excitations beyond the ?Sz = 2, emphasizing the key role played by the crystal lattice as a reservoir of angular momentum that complements the quanta carried by the absorbed and emitted photons. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q57.00002: Hot magnon gas as an amplifier of a localized low-frequency mode Petro Artemchuk, Vasyl S Tyberkevych, Andrei N Slavin Rapid cooling of a hot magnon gas leads to significant accumulation of magnons at the minimum of the magnon spectrum [1], which causes an increase of a chemical potential of the magnon gas and may lead to Bose-Einstein condensation of magnons [1, 2]. Although magnons tend to accumulate at the bottom of the spin-wave spectrum, some magnetic systems also have isolated modes (IM) having frequencies below the continuous spectrum of propagating spin waves [3]. We developed a simple model of interaction of an IM with a hot magnon gas in the process of rapid cooling. We demonstrated that in such a system four-magnon scattering leads to an additional contribution to IM damping ΔΓ ∝ (hf0 - μ), where f0 is the frequency of IM and μ is the chemical potential of the magnon gas. Thus, if the chemical potential of the magnon gas exceeds the IM frequency, ΔΓ becomes negative, which leads to IM amplification. Numerical simulations based on kinetic equations for magnon population numbers [1] confirm our analytical predictions. We discuss several possible setups in which this phenomenon can be observed experimentally. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q57.00003: Temperature dependent magnetization of individual, substrate-free YIG bridges measured using cantilever magnetometry Francisco Ayala Rodriguez, Philip Trempler, Inhee Lee, Shekhar Das, Matt Shmukler, Guanzhong Wu, Georg Schmidt, P Chris Hammel Yttrium iron garnet (Y3Fe5O12), or YIG, is an insulating ferrimagnet whose extremely low magnetic loss makes it attractive for many research and technological applications. Many applications require thin films that are deposited on lattice-matched gadolinium-gallium-garnet (GGG). These films often exhibit a saturation magnetization significantly exceeding theoretical values; this may arise from their interactions with the substrate. Using a novel sample preparation technique, micron sized YIG structures have been separated from the GGG substrate. This allows individual, substrate-free micron bridges to be transferred to a silicon nitride cantilever for cantilever magnetometry measurements. The variation of the resonant frequency of the cantilever as a function of applied magnetic field allows the magnetization and magnetic anisotropy to be determined. We report on these quantities as a function of temperature. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q57.00004: Oscillations and confluence in three-magnon scattering of ferromagnetic resonance Alex Hamill, Tao Qu, Randall H Victora, Paul A Crowell The ferromagnetic resonance (FMR) magnon mode can become unstable above a threshold magnon population, returning to this threshold through three-magnon scattering; this is referred to as the first-order Suhl instability. We have investigated this instability in the time domain over a wide range of excitation powers through homodyning spectroscopy and micromagnetic simulations. We observe a regime that hosts nonequilibrium oscillations of the FMR magnon population. We have developed a model that predicts these oscillations and shows strong qualitative agreement with our results. Notably, these oscillations generate 180° phase shifts of the FMR magnons at high powers. Furthermore, we find that these phase shifts correspond to reversals in the three-magnon scattering direction, between splitting and confluence. These reversals also occur after turning off the microwave excitation, generating prolonged oscillations in the magnon populations. These findings shed new light on the nonequilibrium behavior of three-magnon scattering and the essential role of phase dynamics in magnon scattering processes. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q57.00005: Sagnac interferometry for high-sensitivity spin-orbit torque measurements with the ferromagnetic insulator bismuth-substituted yttrium iron garnet (Bi:YIG) Yunqiu (Kelly) Luo, Rakshit Jain, Bharat Khurana, Caroline A Ross, Daniel C Ralph We utilize Sagnac interferometry for magneto-optic Kerr effect measurements of spin-orbit torque from heavy metals acting on the ferrimagnetic insulator Bi:YIG. The high sensitivity of Sagnac interferometry permits the first-time optical quantification of spin-orbit torque (SOT) from small-angle magnetic tilting of insulating ferromagnetic samples with perpendicular magnetic anisotropy (PMA). This is a fundamentally different method of measuring spin-orbit torque compared to transport measurements based on the spin Hall magnetoresistance (SMR) effect. We study 10 nm thick films of Bi:YIG grown by pulsed laser deposition from a target with composition BiY2Fe5O12 onto a GSGG (Gd3Sc2Ga3O12) substrate. Epitaxial growth yields a film with perpendicular magnetic anisotropy, low coercivity, and low damping, and with a high magneto-optical figure of merit defined as Faraday rotation/optical absorption. We will first elaborate on the mechanism of our Sagnac method, and then discuss questions and insights that arise from comparing the Sagnac SOT readout based on the polar magneto-optical Kerr effect with conventional transport SOT readout based on SMR. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q57.00006: Spin wave propagation in a magnonic crystal with a tailored defect Cesar L Ordonez Romero, Zorayda Lazcano-Ortiz, Giuseppe Pirruccio, Michal Urbánek, Tomáš Hrncír, Naser Qureshi, Oleg Kolokoltsev, Guillermo G Monsivais, Aleksey Ustinov, Andrey Drozdovskyi, David Ley-Domínguez, H. J. Jason Liu The introduction of tailored defects in a magnonic structure could lead to scenarios where the connection between fundamental physics and technological applications can develop the next generation of high frequency microwave devices. The study of magnonic crystals itself have inspired multiple investigations on the behavior of the amplitude frequency characteristic as a function of different structural parameters. However, up to now, most of the scientific reports deal exclusively with the resulting spin wave spectrum for the complete structure and little has been said about the behavior of the spin wave inside the defects. Here, we present a detailed study of the propagation and evolution of surface spin waves (MSSW) through a MC with broken translational symmetry, the influence of the defect in the spin wave propagation, the evolution of frequency bandgaps inside the MC, and the spatial energy distribution as a function of frequency and position. A time and space resolved magneto inductive probing system has been used to map the spin wave propagation in a magnonic crystal with tailored defects. The results show that the spin wave modes get trapped by the defect and the energy is localized in the space for specific frequencies. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q57.00007: Control of magnon-photon coupling by spin torques Anish Rai, Benjamin M Jungfleisch Magnons, the quantum mechanical excitation of spin waves, in magnetically order system can couple with microwave photons via dipolar interaction demonstrating level repulsion (coherent coupling) of the hybridized modes. However, there can be also the coalescence of hybridized modes resulting in level attraction (dissipative coupling). This work examines the role of damping and field-like torques in the magnon-photon coupling by classically integrating the generalized Landau-Lifshitz-Gilbert equation with RLC equation in which a phase correlation between dynamic magnetization and microwave current through combined Ampere and Faraday effects are considered. Our analysis suggests that it is possible to enhance the coupling strength for level repulsion if a certain magnitude and direction of the dc current density is reached for an intermediate value of damping parameter (10-3). However, the toggling between coherent and dissipative coupling is not possible using the spin torques. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q57.00008: Temporal-domain magnonic Mach-Zehnder interferometer Cody A Trevillian, Vasyl S Tyberkevych Emerging quantum magnonic technologies [1–3], such as, e.g., single magnon sources [2] and fabrication methods for strong on-chip magnon-photon coupling [3], necessitate the further study of single magnon decoherence (SMD) mechanisms. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q57.00009: Caustic spin wave beams in an extended thin film excited by a nanoconstriction Dinesh Wagle, Mojtaba Taghipour Kaffash, Loic Temdie Kom, Hicham Majjad, Romain Bernard, Vincent Vlaminck, M. Benjamin Jungfleisch The ability to control the directionality of spin waves is important for magnonic logic and computing applications. Here, we demonstrate the emission of caustic-like spin waves in an extended 200 nm thick yttrium iron garnet (YIG) film from a nano-constricted $rf$ waveguide. Using spatially resolved micro-focused Brillouin light spectroscopy in both the backward volume and the Damon-Eshbach geometry, we reveal the propagation of two spin-wave beams directly emitted from the constriction. We find on one hand that these beams are symmetrical in intensity when the $rf$ magnetic field is perpendicular to the applied magnetic field. On the other hand, one beam is more intense than the other one when the $rf$ magnetic field is parallel to the external field. We further study the frequency dependence of the propagation direction of these caustic-like spin wave beams. Our findings have important implications for the development of switchable spin wave splitters, passive spin-wave frequency-division demultiplexers and magnonic interferometry. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q57.00010: Non-local magnon transport in Pt/Li0.5Al1.0Fe1.5O4 systems Xin Yu Zheng, Sanyum Channa, Tian-Yue Chen, Haowen Ren, Zbigniew Galazka, Andrew D Kent, Yuri Suzuki Spin wave-based electronics rely on the existence of low damping magnetic insulators for coherent excitation and propagation of spin waves. Toward this end, it is important to study non-local magnon transport in such systems to gauge their promise as media for spin wave transport. Previously, we demonstrated the synthesis of the novel spinel oxide magnetic insulator Li0.5Al1.0Fe1.5O4 (LAFO) films on (001) oriented MgGa2O4 (MGO) and MgAl2O4 (MAO) substrates that possess a Gilbert damping parameter on the order of 10-3. In this talk, we present our results on non-local magnon transport in LAFO/MGO and LAFO/MAO systems, in which LAFO exhibits strain-induced perpendicular magnetic anisotropy and easy-plane magnetic anisotropy respectively. By studying the non-local voltage amplitude generated via the inverse spin Hall effect as a function of the separation of two overlaying Pt electrodes, we extract a spin diffusion length in LAFO of 1.8 um. This large spin diffusion length corroborates the low damping in LAFO and shows the promise of LAFO as a candidate material for future spintronics applications. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q57.00011: Determination of magnetic anisotropy due to spin-orbit coupling in Fe (II) spin crossover thin film Ashley Dale, Saeed Yazdani, Thilini K Ekanayaka, Esha Mishra, Yuchen Hu, Peter A Dowben, John W Freeland, Jian Zhang, Horia I Petrache, Ruihua Cheng Spin crossover molecules such as [Fe(H2B(pz)2)2(bipy)] (pz=pyrazol−1−yl, bipy=2,2’−bipyridine) are candidates for molecular spintronics and promise ultrafast and low-power devices for data storage and magnetic sensing. Most recently, this molecule has been coupled to a ferroelectric and shown to undergo a non-volatile, isothermal, reversible spin-state transition at room temperature. The spin state transitions may also be controlled by an external magnetic field, which calls for better understanding of the transition mechanism. Recently conducted field dependent, temperature dependent, and orientation dependent X-ray magnetic circular dichroism experiments on a 60 nm [Fe(H2B(pz)2)2(bipy)] thin film deposited on a SiO2 substrate show that the orbital moment of the molecule is soft to the magnetic field, and the hard axis of the magnetic moment is along the thin film surface normal direction. These results can be interpreted within the context of a 3D Ising model Hamiltonian with a magnetic field term, where an anisotropic energy barrier is observed in the high spin state of the molecule. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q57.00012: Spintronics-Compatible Approach to Solving Maximum-Satisfiability Problems with Probabilistic Computing, Invertible Logic, and Parallel Tempering Giovanni Finocchio This work will show recent results on Ising machines (IMs) and their potential hardware implementation with spintronic technology focusing on IMs built with p-bits (probabilistic |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q57.00013: Topologically Frustrated Bonding in [2]Triangulene Chains matthew d rollings Carbon nanomaterials offer advantages for advanced computing devices such as atomically precise design and low spin-orbit. In this work, the smallest open-shell alternant polyaromatic hydrocarbon, phenalenyl, was chosen to target a 1-dimensional all-carbon spin-1/2 chain. A dibromo-phenalene monomer was synthesized and sublimed onto and polymerized on a Au (111) surface under ultra-high vacuum conditions and characterized using low temperature scanning tunneling microscopy. A lone phenalenyl radical (n = 1 system) on the surface exhibits Kondo resonance expected from an open-shell impurity. However, dimer structures (n = 2 system) appear to hybridize neighboring non-bonding modes, opening a gap around the fermi level (EF). The magnitude of the opened gap is lower than expected for hybridized molecular orbitals, at ~100 meV. Further, the phenalenyl dimer has a non-Kekulé resonance structure in which the two radicals cannot be paired into a π-bond, a property known as topological frustration. This behavior is rationalized using a one-site tight-binding model with effective hopping parameter (τ). Including the 3rd-nearest-neighbor coupling in the atomistic model is the minimum level of theory necessary to capture the observed bonding behavior. The bonding interactions occur exclusively by virtue of the 3rd-nearest-neighbor coupling between molecular units connected solely by a σ-bond between atoms with no density of the molecular orbitals comprising the interaction. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q57.00014: Deep Physical Reservoir Computing with Programmable Nanomagnetic Hierarchies Kilian Stenning, Jack C Gartside, Luca Manneschi, Christopher Cheung, Tony Chen, Jake Love, Alexander L Vanstone, Holly Holder, Francesco Caravelli, Karin Everschor-Sitte, Eleni Vasilaki, Will R Branford Nanomagnetic artificial spin-systems are ideal candidates for neuromorphic hardware. Their passive memory, state-dependent dynamics and nonlinear GHz spin-wave response provide powerful reservoir computation1,2 (RC). |
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