Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session S18: Magnetic Thin FilmsFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Burm Baek, NIST Room: 317 |
Thursday, March 17, 2016 11:15AM - 11:27AM |
S18.00001: Imaging of precessional phase variations in spin Hall devices using picosecond heat pulses Feng Guo, Jason Bartell, Gregory Fuchs We introduce a new approach of studying the spin Hall effect in patterned magnetic multilayers by imaging ferromagnetic resonance (FMR) precession phase. Using time-resolved anomalous Nernst effect (TRANE) microscopy, we quantify the amplitude and phase of local magnetic precession, which allows us to image the total driving field vector orientation. In a 5 $\mu $m wide channel, we observe a substantial variation of the driving field vector as a function of lateral position that we attribute to variations in the total Oersted field angle and the demagnetization field. Next, using the same device, we compare TRANE phase imaging measurements to all-electrical spin-transfer torque ferromagnetic resonance (STFMR) measurements that sense the spatially averaged precession phase. We find that spatial phase variations introduce a systematic error in the spin Hall efficiency measured using conventional STFMR analysis in our devices. These results underscore the importance of phase-sensitive dynamic imaging to augment all-electrical FMR techniques in quantifying the spin Hall efficiencies of devices. [Preview Abstract] |
Thursday, March 17, 2016 11:27AM - 11:39AM |
S18.00002: Magnon excitation and transport in Ferromagnetic Insulator/metal multilayers Tao Liu, Jie Ren, Jianwei Zhang We studied magnon excitation and transport in a Ferromagnetic Insulator(FI) layer(such as YIG), which connected with Ferromagnetic/normal metal multilayers in two sides. In our modeling, we adopted self-consistent spin dependent Boltzmann equations in metal layers and magnon Boltzmann equation in FI layer. When applying an in-plane current in FM layer, a transverse spin current was generated due to Anomalous Hall effect, after crossing normal metal layer, it will produce magnon excitation at N/FI interface. With carrying spin information, magnon excitation in FI can eventually excite a new spin current at second F/N interface. This is so call magnon-drag effect [1]. In our work, we focused on magnon propagation in FI, with all two-magnon, three magnon, and four magnon scattering. Associated with spin dependent Boltzmann equation, we can investigate magnon excitation and transport properties in FI layer from the interface to bulk scale. The magnon excitation in FI layer is dominated not only by the interface interaction at Normal/FI boundary, but also by the bulk scattering in FI. Our results show the magnon in FI layer has decay behaviors to low energy model. We also showed a new way to manipulate magnon transport in FI. [1] S.L. Zhang and S. Zhang, PRL,109,096603(2012) [Preview Abstract] |
Thursday, March 17, 2016 11:39AM - 11:51AM |
S18.00003: ABSTRACT WITHDRAWN |
Thursday, March 17, 2016 11:51AM - 12:03PM |
S18.00004: Unveiling magnetic Hysteresis Paula Mellado, Andres Concha, David Aguayo Hysteresis manifests as the lack of retraceability of the magnetization curve in magnetic systems. It has been associated with rotation of magnetization and changes of magnetic domains. However, up to date there has been no realization that allows to separate these coupled mechanisms. We introduce a minimal magnetic system where hysteresis is realized in a simple and minimal fashion. The basic units are a few U(1) ferromagnetic altitudinal rotors placed along a one dimensional chain. They exhibit a dissipative dynamics, interacting via magnetic coupling among them and via Zeeman interaction with the external magnetic field. The system displays a hysteretic behavior starting with N=2 rotors which remains qualitatively invariant as more magnets are added to the chain. We explain this irreversibility by using a model that includes Coulombic interactions between magnetic charges located at the ends of the magnets, zeeman coupling and viscous dissipation. We show that interactions between the unit components is the key element responsible for hysteresis and find that the ability to perceive hysteresis, depends on how the time frequencies of damping and interactions inherent to the system compare with the time frequency set by the external field ramping rate. [Preview Abstract] |
Thursday, March 17, 2016 12:03PM - 12:15PM |
S18.00005: Combined Molecular Dynamics-Spin Dynamics Simulation of $\alpha$-Iron in an External Magnetic Field Mark Mudrick, Dilina Perera, David P. Landau Using an atomistic model that treats both translational and spin degrees of freedom, combined molecular and spin dynamics simulations have been performed to study dynamic properties of $\alpha$-iron. Atomic interactions are described by an empirical many-body potential\footnote{Dudarev S L, Derlet P M 2005 \textit{J. Phys.: Cond. Matter} \textbf{17} 7097} while spin-spin interactions are handled with a Heisenberg-like Hamiltonian with a coordinate dependent exchange interaction\footnote{Ma P W, Woo C H, Dudarev S L 2008 \textit{Phys. Rev. B} \textbf{78} 024434}. Each of these interactions are parameterized by first-principles calculations. These simulations numerically solve equations of motion using an algorithm based on the second-order Suzuki-Trotter decomposition for the time evolution operator\footnote{Perera D, et al. 2014 \textit{J. Phys.: Conf. Ser.} \textbf{487} 012007}. Through calculation of the Fourier transform of space-displaced time-displaced correlation functions, vibrational and magnetic excitations have been studied. The application of an external magnetic field up to 10-T has now been included and has been shown to increase the characteristic frequencies of the single-spin-wave excitations. Two-spin-wave interactions have also been investigated. [Preview Abstract] |
Thursday, March 17, 2016 12:15PM - 12:51PM |
S18.00006: Magnetic dynamics studied by high-resolution electron spectroscopy and time-resolved electron microscopy. Invited Speaker: Rajeswari Jayaraman Future information technology requires an increased magnetically encoded data density and novel electromagnetic modes of data transfer. While to date magnetic properties are observed and characterized mostly statically, the need emerges to monitor and capture their fast dynamics. In this talk, I will focus on the spin dynamics i.e. spin wave excitations and the dynamics of a new topological distribution of spins termed ``skyrmions''. Wave packets of spin waves offer the unique capability to transport a quantum bit, the spin, without the transport of charge or mass. Here, large wave-vector spin waves are of particular interest as they admit spin localization within a few nanometers. By using our recently developed electron energy loss spectrometer, we could study such spin waves in ultrathin films with an unprecedented energy resolution of 4 meV. By virtue of the finite penetration depth of low energy electrons, spin waves localized at interfaces between a substrate and a thin capping layer can be been studied yielding information about the exchange coupling between atoms at the interface. The quantization of spin waves with wave vectors perpendicular to the film gives rise to standing modes to which EELS has likewise access. Such studies when carried out as function of the film thickness again yield information on the layer dependence of the exchange coupling. Magnetic skyrmions are promising candidates as information carriers in logic or storage devices. Currently, little is known about the influence of disorder, defects, or external stimuli on the spatial distribution and temporal evolution of the skyrmion lattice. In this talk, I will describe the dynamical role of disorder in a large and flat thin film of Cu$_2$OSeO$_3$, exhibiting a skyrmion phase in an insulating material. We image up to 70,000 skyrmions by means of cryo-Lorentz Transmission Electron Microscopy as a function of the applied magnetic field. In the skyrmion phase, dislocations are shown to cause the emergence and switching between domains with different lattice orientations, and the temporal fluctuation of these domains is filmed. These observations pave the way to the control of a large 2D array of skyrmions. [Preview Abstract] |
Thursday, March 17, 2016 12:51PM - 1:03PM |
S18.00007: Collective Mode Splitting in Coupled Ferromagnet/Oxide Heterostructures Juan G. Ramirez, J. de la Venta, Siming Wang, Thomas Saerbeck, Ali C. Basaran, X. Batlle, Ivan K. Schuller The coupling of electronic, magnetic, and structural properties between two dissimilar materials in contact can induce novel functionalities. Here we report on a drastic modification of the magnetization dynamics of thin Nickel films in Ni/V$_{\mathrm{2}}$O$_{\mathrm{3}}$ bilayers. We performed temperature-dependent ferromagnetic resonance measurements across the first-order structural phase transition (SPT) of V$_{\mathrm{2}}$O$_{\mathrm{3}}$. The results show a strong coupling of the V$_{\mathrm{2}}$O$_{\mathrm{3}}$ lattice dynamics to the magnon spectra of the Ni film in proximity. We have performed similar measurements across the second-order SPT in Ni/SrTiO$_{\mathrm{3}}$ hybrids. In this later case, only a slight change of the static magnetization was found with no modification of the magnetization dynamics. Our results suggest that the phase coexistence across the first-order SPT of V$_{\mathrm{2}}$O$_{\mathrm{3}}$ is responsible for the effects observed in the Ni/V$_{\mathrm{2}}$O$_{\mathrm{3}}$ hybrids. This suggests the existence of similar effects in other hybrid materials with first-order structural phase transitions. [Preview Abstract] |
Thursday, March 17, 2016 1:03PM - 1:15PM |
S18.00008: Localized spin wave modes in parabolic field wells Robert McMichael, Elena Tartakovskaya, Martha Pardavi-Horvath We describe spin wave modes trapped in parabolic-profile field wells. Trapped spin waves can be used as local probes of magnetic properties with resolution down to 100 nm in ferromagnetic resonance force microscopy.[1,2] Localized modes have been shown to form around field minima from a number of sources, including stray fields from magnetic probe tips [1,3-4] and inhomogeneous magnetostatic fields near film edges.[2] Here, we address the most basic trap, which is a parabolic minimum in the applied field. The magnetic eigenmodes in this trap are tractable enough to serve as approximations in more realistic situations. For a parabolic field, we select basis mode profiles proportional to Hermite functions because they are eigenfuctions of the applied field and exchange parts of the equations of motion. Additionally, we find that these Hermite modes are approximate eigenfunctions of magnetostatic interactions, showing good agreement with micromagnetic calculations. More precise agreement is achieved by diagonalizing the equations of motion using only a few modes. 1. I. Lee et al., Nature 466, 845 (2010). 2. F. Guo et al. Phys. Rev. Lett, 110, 017601 (2013) 3. H.-J. Chia,et al., Phys. Rev. Lett. 108, 087206 (2012). 4. R. Adur et al, Phys. Rev. Lett. 113, 176601 (2014). [Preview Abstract] |
Thursday, March 17, 2016 1:15PM - 1:27PM |
S18.00009: Cavity mediated coherent coupling between yttrium iron garnet magnets Nicholas Lambert, James Haigh, Stefan Langenfeld, Andrew Doherty, Andrew Ferguson Strong coupling between the magnetostatic modes of an yttrium iron garnet (YIG) magnet and a microwave frequency electromagnetic cavity is now readily achievable[1,2,3]. Recently, coupling between a magnon and a superconducting qubit mediated by a cavity has also been demonstrated[4]. In this talk, we describe dispersive measurement[5] of the cavity-mediated coupling of magnetostatic modes in two YIG magnets. We find they are strongly coupled even when detuned from the cavity modes. We study the strength of the coupling as a function of the detuning, and find a $1/\Delta$ dependence when close to individual cavity modes. Dark states of the coupled magnets are observed, in which the symmetry of the microwave drive does not match that of the new eigenstates. Our results are described well within the framework of circuit QED. Such an approach to coupling magnets might be used to phase-lock many spatially separated magnetic oscillators, such as those in spin-torque nano-oscillators or magnetic metamaterials. [1] Huebl et al., Phys. Rev. Lett., 111, 127003 (2013) [2] Zhang et al., Phys. Rev. Lett., 113, 156401 (2014) [3] Lambert et al., J. Appl. Phys., 117, 053910 (2015) [4] Tabuchi et al., Science, 349(6246), 405–408 (2015) [5] Haigh et al., Phys. Rev. B, 91, 104410 104410 (2015) [Preview Abstract] |
Thursday, March 17, 2016 1:27PM - 1:39PM |
S18.00010: Rabi nutations in a ferromagnetic film Amir Capua, Charles Rettner, Stuart Parkin When electromagnetic radiation interacts with a two-level system, energy is transferred back and forth between the quantum system and the electromagnetic radiation at a rate defined by the Rabi frequency. This process takes place as long as coherence prevails, until steady state is reached. Rabi nutations have been observed in a variety of quantum systems (atomic vapors, semiconductors, superconducting qubits, etc.). Here, we observe Rabi nutations in an ultrathin \textasciitilde 10 {\AA} perpendicularly magnetized CoFeB film. A hybrid ferromagnetic resonance (FMR) -- time resolved magneto optical Kerr effect (TRMOKE) system is used for this observation. Namely, a strong optical pump pulse perturbs the precessing spin system after which a weak optical probe pulse is sent at different times to map its recovery until steady precessional motion is reached again. The responses at the different detunings of magnetic field away from resonance conditions readily indicate the occurrence of the Rabi nutations which are initiated by the pump arriving at t$=$0. Excellent agreement with the prediction given by the Rabi formula is found. The method we report presents a new approach to study dynamical phenomena in magnetic materials. [Preview Abstract] |
Thursday, March 17, 2016 1:39PM - 1:51PM |
S18.00011: Propagation of pulsed surface spin-wave signals at millikelvin temperatures Arjan van Loo, Richard Morris, Alexy Karenowska Propagating microwave-frequency magnons in magnetic films attract increasing attention on account of their potential interface with superconducting quantum circuit and qubit systems. Their rich dynamics and slow speeds make magnons an interesting addition to the circuit quantum electrodynamics toolbox and, at the same time, superconducting circuit technology promises to be a powerful tool in the investigation of their quantum properties. We have studied the propagation of pulsed surface spin-wave signals over millimeter distances in yttrium iron garnet waveguides at $\sim10\,\rm{mK}$. Input microwave pulses and pulse trains with various envelope shapes were applied to an inductive input antenna, and the resulting magnons were detected by an output antenna of identical design. The shape of the output signal was observed to depend on the frequency content (carrier and pulse shape) of the input pulse. By performing measurements at varying frequencies and magnetic fields we have been able to map out the dispersion relation for surface magnon modes. These experiments were undertaken as a first step towards coupling propagating magnons in thin films to other quantum systems with microwave-frequency transition energies, and superconducting qubits in particular. [Preview Abstract] |
Thursday, March 17, 2016 1:51PM - 2:03PM |
S18.00012: Spin waves of ferromagnetic films Rodrigo Arias The spin wave modes of ferromagnetic films have been studied for a long time experimentally as well as theoretically: initially magnetostatic and later dipole-exchange modes. Theoretically dipole-exchange modes have been solved exactly numerically for some configurations and boundary conditions, and there are approximations of their frequency dispersion relations based on infinite series solutions and perturbation theory, valid for arbitrary orientations of an applied magnetic field, and for boundary conditions that allow varying degrees of pinning. A theoretical method that allows to determine with ease the exact frequency dispersion relations of the dipole-exchange modes is presented: it is required to solve numerically a 6x6 linear eigenvalue problem at each wavevector of interest; the spin wave modes inside or outside the sample may be plotted. Analogous calculations may be done to determine magnetostatic modes in detail. The method corresponds to a generalization of Green's theorem to the problem of determining the dipole-exchange modes of a ferromagnetic film: convolution integral equations for the magnetization and magnetostatic potential are derived on the surfaces of the film that become simple local algebraic equations in Fourier space, or for specific wavevectors. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700