Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F47: Spin Wave Excitation, Manipulation, and DetectionFocus
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Sponsoring Units: GMAG Chair: Lijun Zhu Room: 710/712 |
Tuesday, March 3, 2020 8:00AM - 8:36AM |
F47.00001: Strongly coupled magnon hybrid systems with permalloy thin films1 Invited Speaker: Yi Li Recently, magnon-based hybrid systems have attracted increasing interests as a new branch in spintronics research2-5. Magnons can be coupled to a wide variety of excitations including microwave photons, optical photons, phonons, and other magnons. In addition, the excitation frequency of magnons can be easily tuned by an external magnetic field, which is highly desirable for controllable hybrid systems. Up to date, most studies are based on low-damping yttrium ion garnet (YIG) spheres or thick films, which are beneficial for strong coupling strength but unfavorable for scalable on-chip-integrated applications. |
Tuesday, March 3, 2020 8:36AM - 8:48AM |
F47.00002: Strong Interlayer Magnon-Magnon Coupling in Magnetic Hybrid Nanostructures Jilei Chen, Chuanpu Liu, Tao Liu, Yang Xiao, Ke Xia, Gerrit Bauer, Mingzhong Wu, Haiming Yu Strong couplings between magnons and photons have recently attracted lots of attention due to potential applications in quantum computing by utilizing coherent couplings between spins and superconducting qubits. Here, I will present our recent experimental results on strong interlayer magnon-magnon coupling in an on-chip nanomagnonic device at room temperature [1]. Ferromagnetic nanowire arrays are integrated on a 20-nm-thick yttrium iron garnet (YIG) thin film strip. Large anticrossing gaps up to 1.58 GHz are observed between the ferromagnetic resonance of the nanowires and the in-plane standing spin waves of the YIG film. The coupling strength is tunable by the magnetic configuration, allowing the coherent control of magnonic devices. |
Tuesday, March 3, 2020 8:48AM - 9:00AM |
F47.00003: Introducing Coherent Time Control to Cavity Magnon Polartion Modes Tim Wolz, Alexander Stehli, Andre Schneider, Isabella Boventer, Rair Macedo, Alexey V. Ustinov, Mathias Klaeui, Martin Weides By connecting light to magnetism, cavity-magnon-polaritons (CMPs) [1-3] can link quantum computation to spintronics. Consequently, CMP-based information processing devices have thrived over the last years, but have almost exclusively been investigated with single-tone spectroscopy. However, universal computing applications will require a dynamic control of the CMP on demand and within nanoseconds. In this work [4], we perform fast manipulations of the different CMP modes with independent but coherent pulses to the cavity and magnon system. We change the state of the CMP from the energy exchanging beat mode to its normal modes and further demonstrate two fundamental examples of coherent manipulation: First, a dynamic control over the appearance of magnon-Rabi oscillations, i.e., energy exchange, and second, energy extraction by applying an anti-phase drive to the magnon. Our results show a promising approach to control different building blocks for a quantum internet and pave the way for further magnon-based quantum computing research. |
Tuesday, March 3, 2020 9:00AM - 9:12AM |
F47.00004: Nanoscale Detection of Magnon Excitations with Variable Wavevectors Through a Quantum Spin Sensor Eric Lee-Wong, Ruolan Xue, Feiyang Ye, Andreas Kreisel, Toeno van der Sar, Amir Yacoby, Chunhui Du Control and manipulation of pure spin currents in magnetic insulators has been a central focus of modern spintronic research. Building on the transformative nitrogen vacancy (NV) based quantum sensing platform, we have achieved local detection of a range of spin wave modes in magnetic insulator Y3Fe5O12 thin films over a 100-nanometer length scale. Through the multi-magnon scattering process, the excited spin waves generate fluctuating magnetic fields at the NV electron spin resonance frequencies, accelerating the relaxation of the NV spin. By measuring the variation of the emitted photoluminescence of the NV center, the detailed information of the magnon modes can be optically accessed, providing a unique window to reveal the local magnetic properties of the studied materials. Our findings highlight the significant opportunities offered by NV spin quantum sensors in exploring nanoscale spin dynamics of emergent spintronic systems. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F47.00005: Spin wave resonance study in a series of etched GaMnAsP films Xinyu Liu, Seul-Ki Bac, Sanghoon Lee, Malgorzata Dobrowolska, Jacek K. Furdyna, Henryk Puszkarski, Piotr Tomczak Although ferromagnetic semiconductor films have already been investigated for the last two decades, some fundamental issues still puzzle the researchers in this field. One of these issues is how the magnetic anisotropy field distributes along the growth direction. In order to resolve this issue in a 108-nm GaMnAsP film, a series of etched samples formed by wet-etching this GaMnAsP film were studied by XRD, SQUID and FMR. The thicknesses of the etched GaMnAsP films were determined by XRD measurements, using the oscillations observed in ω-2θ scans. The XRD peaks from GaMnAsP films are also used for determine the Mn and P contents along the growth direction. Magnetizations of the films are measured by SQUID as a function of field and temperature. FMR measurements were carried out at 4K as function of field orientation, using both out-of-plane and in-plane geometries. A series of spin wave modes are observed when field is applied in the plane of film, as well a critical angle phenomenon is found in specific resonance configurations. The angular dependence of spin wave modes will be analyzed using newly reported spherical surface pinning model in order to map the surface free energy. The results will be summarized as a function of film thickness for all etched samples. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F47.00006: Strong angle dependence of auto-oscillating spin wave multi-modes in constricted Py/Pt bilayers Inhee Lee, Chi Zhang, Simranjeet Singh, Brendan McCullian, P Chris Hammel Spin-orbit torque driven auto-oscillators (AO) in constricted bilayers can be highly coherent and tunable, even at room temperature. However, the dissipation mechanisms of AO confined by a constriction remain unclear. We have studied the dependence of several AO modes on the angle between the current flow and an in-plane applied magnetic field in a 0.6 μm x 1 μm Py/Pt bilayer. We observe considerable changes in the size, number, and distribution of modes as the angle varies. The spatial profiles of the modes are identified using micromagnetic simulation, and classified into three types: edge, center-like, and their combination. We also characterize the AO modes in terms of resonance frequency, linewidth and power. Beyond a threshold current, the power in the lowest order mode saturates and its linewidth increases. However, this coincides with enhanced excitation of higher order modes such that the power summed over all modes continues to grow with current. We achieve ~ 8 MHz minimum linewidth and ~ 0.5 pW maximum power at 77 K from the lowest order mode at an angle of 65 degree, though below 120 K, the improvement of the mode for the narrower linewidth and the stronger power with decreasing temperature is reduced. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F47.00007: Influence of ferromagnetic films surface properties on spin wave modes Rodrigo Arias, Ignacio Armijo The frequencies of propagating spin waves in ferromagnetic films may be determined experimentally with some precision, and reflect the surface properties of the films. In particular, if the surface properties break symmetries between both surfaces, there will be frequency non reciprocity between spin waves that travel in different directions. Furthermore, there is possible shape non-reciprocity of the spin waves even for symmetric films. Thus, in order to relate surface properties to the behavior of spin waves, we study theoretically, within the micro magnetic approximation, spin wave modes under obliquely applied magnetic fields to the film, since in this case the surface properties have a more clear influence in the spin wave properties. For this case the equilibrium magnetization is non-uniform, it deflects close to the surfaces, due to effective surface boundary conditions that model local surface fields. We use the Extinction-Green theorems to determine the spin wave modes, solving numerically differential equations along the transverse direction for the so called auxiliary functions, and we interpret these numerical results by use of the WKB approximation. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F47.00008: Quantitative Study of Spin Wave Chirality in Obliquely Magnetized Magnetic Films Cody Trevillian, Vasyl S Tyberkevych Dipole-dipole interaction in thin magnetic films leads to formation of parity-breaking (i.e., chiral) spin wave (SW) modes, such as, e.g., chiral magnetostatic surface SW (CMSSW) [1] & heterosymmetric SW (HSSW) [2] having a number of unique properties. However, a general theory of the origin of chiral spin wave formation & their chiral properties in obliquely magnetized magnetic films (OMMF) remains absent. Here, we propose a quantitative measure of SW chirality, Cn = 1 – │〈Ρ〉n│, where 〈Ρ〉n is the expected value of the parity operator for the nth SW mode. Using Kalinikos-Slavin's theory of SW spectrum in OMMF [3], we performed quantitative study of formation of chiral SWs. We show that total parity ∑n〈P〉n of all SW modes is approximately conserved, which implies that SW modes acquire chiral properties in pairs through the “parity exchange” mechanism. In particular, we demonstrate formation of strongly chiral modes at odd crossing points of SW spectrum & show that chirality of both CMSSW & HSSW is a result of “parity exchange” between two lowest symmetric & antisymmetric SW modes. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F47.00009: Probing phase transition and anisotropy in magnetic insulator based heterostructures employing magnon spin currents Kingshuk Mallick, Aditya A Wagh, Adrian Ionescu, Crispin H.W. Barnes, P.S. Anil Kumar Many reports have explored the temperature dependence of Longitudinal Spin Seebeck Effect (LSSE) in insulating magnets. However, there has been a longstanding disparity between theory and experimental evidence with regards to the nature of power law decay of the LSSE while approaching the ferromagnetic phase transition temperature (TC). We investigate bilayers of Pt/La2NiMnO6 (LNMO) and Pt/EuO1-X, both predicted to be promising candidates for spintronics. Our findings reveal that the signal near TC can be fitted to a power law of the form (TC-T)P. We explain our results based on the magnon-driven thermal spin pumping theory. We comprehensively demonstrate correlation between the critical exponents of LSSE and magnetization for both FMs. Interestingly, the exponent, P, remained invariant upon varying the crystallinity in LNMO. In contrast, Spin Hall Magnetoresistance (SMR) measurements on epitaxial LNMO, exhibit distinctly different features. The observed behavior in epitaxial films appears to be dominated by the interface magnetic anisotropy. In addition, we observe SMR and Anisotropic Magnetoresistance (AMR) in Pt/EuO1−X thin films. We deduce possible explanations based on the temperature dependence of EuO1−X bandstructure and spin mixing conductance of the Pt/EuO1−X interface. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F47.00010: Tuning entanglement by squeezing magnons in anisotropic magnets Ji Zou, Se Kwon Kim, Yaroslav Tserkovnyak We theoretically study the entanglement between two arbitrary spins in a magnetic material, where magnons naturally form a general squeezed coherent state, in the presence of an applied magnetic field and axial anisotropies. Employing concurrence as a measure of entanglement, we demonstrate that spins are generally entangled in thermodynamic equilibrium, with the amount of entanglement controlled by the external fields and anisotropies. As a result, the magnetic medium can serve as a resource to store and process quantum information. We, furthermore, show that the entanglement can jump discontinuously when decreasing the transverse magnetic field. This tunable entanglement can be potentially used as an efficient switch in quantum-information processing tasks. |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F47.00011: Electron-magnon scattering and magnon generated chiral charge and spin pumping from time-dependent-quantum-transport/classical-micromagnetics approach Abhin Suresh, Branislav Nikolic In this study, we employ recently developed [M. D. Petrovic et. al., Phys. Rev. Appl. 10, 054038 2018] multiscale time-dependent-quantum-transport/classical-micromagnetics formalism (TDNEGF-LLG) to simulate how spin-polarized steady state current of electrons interacts with a magnon modelled as a classical spin wave. We investigate electronic spin and charge currents generated by the excitation of a single frequency spin wave in a one-dimensional finite size magnetic nanowire composed of classical local magnetic moments precessing around the anisotropy axis while the phase of the precession of adjacent moments varies harmonically over the wavelength of spin wave with uniform precession cone angle. We show that spin wave hosted in the middle of two metallic leads pumps chiral electronic spin and charge currents into the leads, which can be flipped by reversing the direction of magnonic spin current carried by the spin wave. When steady spin-polarized electronic charge current is injected from the left lead into the region hosting the spin wave, we observed that outgoing electronic charge and spin currents in the right lead can be reduced or enhanced, depending on the direction of magnonic spin current. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F47.00012: Investigation of the magnon dispersion in Lu2V2O7 and magnon Weyl point Seunghwan Do, Jeffrey Rau, Hasitha Suriya Arachchige, Binod K. Rai, Gabriele Sala, Victor R. Fanelli, Matthew Stone, Qing Huang, Haidong Zhou, Mark D Lumsden, Andrew D Christianson The ferromagnetic pyrochlore lattice with Dzyaloshinskii-Moriya (DM) interactions has attracted much attention due to predicted Weyl points in the magnon spectrum [1,2]. The pyrochlore Lu2V2O7 has been suggested as a strong candidate to realize the concept [2]; it has a ferromagnetic ground state below TC~69.5 K [3] and the presence of a magnon Hall effect indicates a strong DM interaction [4]. We use inelastic neutron scattering to examine the spin wave excitations in the compound. These measurements enable us to detect sharp magnon dispersions that are well modeled with linear spin wave theory. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F47.00013: Spin Seebeck Effect in Helimagnetic Cu$_2$OSeO$_3$: Test of Bulk Magnon Spin Current Theory Artem Akopyan, Narayan Prasai, Benjamin Trump, Guy G. Marcus, Tyrel McQueen, Joshua Cohn Cu$_2$OSeO$_3$ exhibits$^a$ the largest magnon thermal conductivity of any known ferro- or ferrimagnet. Here we report temperature ($T$) and magnetic field-dependent measurements of magnon thermal conductivity ($\kappa_m$) and longitudinal spin Seebeck coefficient ($S_{LSSE}$) in 10-nm Pt/Cu$_2$OSeO$_3$ heterostructures for 1~K $\leq T\leq$~15~K. Measurements for three different specimens, having spin-mixing conductances that vary by more than an order of magnitude, demonstrate a relationship between $\kappa_m$ and $S_{LSSE}$ in good agreement with bulk magnon spin current theory. |
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