Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R14: Focus Session: Magneto-thermal Transport and Spin Current in Insulators |
Hide Abstracts |
Sponsoring Units: DMP FIAP GMAG Chair: Helmut Schulthei, Argonne National Laboratory Room: 316 |
Wednesday, March 20, 2013 2:30PM - 2:42PM |
R14.00001: Local spin currents in magnetothermal landscapes M. Weiler, M. Schreier, H. Huebl, M. Althammer, M. Opel, R. Gross, S.T.B. Goennenwein Spin caloritronic effects - such as the spin Seebeck effect - are concerned with the interplay of heat and spin currents and have been experimentally studied using homogeneous thermal gradients to date. However, in order to understand the underlying magnon-phonon interactions that take place on short length scales, a spatially resolved study of spin currents in magnetothermal landscapes~[1] is mandatory. We here use a focussed, scannable laser beam to generate local thermal perturbations in thin film multilayers incorporating the ferromagnetic insulator Y$_3$Fe$_5$O$_{12}$ (YIG). In both, YIG/Pt thin film bilayers and YIG/Au/Pt trilayers, the laser heating results in a difference of the magnon and electron temperatures in the YIG and Pt, respectively, as quantitatively modeled in numerical simulations. In the presence of this temperature difference, we experimentally observe a local in-plane electric field in the YIG/Pt and YIG/Au/Pt samples. This electric field is ascribed to the detection of the local longitudinal spin Seebeck effect via the inverse spin Hall effect in Pt. Our experiments allow to, e.g., electrically image magnetic texture in a magnetic insulator and provide a local, bipolar, magnetically controllable spin current source. [1] M. Weiler et al. PRL 108, 106602 [Preview Abstract] |
Wednesday, March 20, 2013 2:42PM - 2:54PM |
R14.00002: Induced Magneto-transport Effects in Non-magnetic Metals on Yttrium Iron Garnet Tao Lin, Chi Tang, Jing Shi Yttrium iron garnet (YIG) was called ``spin Seebeck insulator,'' for it supports heat-generated pure spin currents. Pt thin film, with strong spin-orbit interaction, is used as a spin current generator or detector based on the spin Hall effect or the inverse spin Hall effect. The combination of these two materials plays a very important role in spintronics. A recent magnetotransport study shows strong evidence of a magnetic proximity effect in thin Pt films deposited on YIG. Here, we present a magneto-transport study of several non-magnetic (NM) metal films (e.g. Pt, Pd) on YIG films grown on gadolinium gallium garnet substrates with laser molecular beam epitaxy. The anisotropic magnetoresistance (AMR) and anomalous Hall effect (AHE) reveal clear ferromagnetic characteristics in NM films. The magnitude of the AHE angle $\Theta $ in Pd/YIG structure increases with decreasing temperature, while $\Theta $ in Pt/YIG structure has a sign reversal at an intermediate temperature. Both AMR and AHE have been investigated as the NM film thickness is varied and an optimal effective thickness is identified. The effect of annealing has also been studied and the results are consistent with the observed thickness dependence. In thin NM films, a ln(T) temperature dependence with a resistivity minimum is observed at low temperatures, suggesting that the Kondo effect may be relevant. Detailed discussions about the origin of these effects will be presented. [Preview Abstract] |
Wednesday, March 20, 2013 2:54PM - 3:06PM |
R14.00003: Nonlocal optical generation of spin and charge currents on the surface of magnetic insulators using total absorption and surface plasmons Siu Tat Chui, Z.F. Lin, C.R. Zhang, John Xiao We study the nonlocal spin and charge current generation in a finite metallic element on the surface of magnetic insulators such as yttrium iron garnet due to the absorption of the magnetic surface plasmon (MSP). Whereas a surface plasmon is completely reflected by a metal, an MSP can be absorbed due to the absence of backward states. The injection of MSP generates a voltage in the longitudinal direction parallel to the wave vector, with the voltage proportional to input power. If the metal is a ferromagnet, a spin current can also be induced in the longitudinal direction. Our results provide a way to improve upon integrated circuits of spintronics and spin wave logic devices. [Preview Abstract] |
Wednesday, March 20, 2013 3:06PM - 3:42PM |
R14.00004: Spin information propagation through metal/magnetic insulator interface Invited Speaker: Shulei Zhang In metal-based spintronics, electron spin current plays pivotal roles in propagating spin information. Here we investigate the propagation of magnon current carried by non-equilibrium magnons, which can also serve as spin carriers in ferromagnet. By exploiting of the semiclassical Boltzmann approach, we explicitly derive the non-equilibrium magnon distribution and magnon current in ferromagnetic insulators [1]. In some limiting cases, we find that magnon density satisfies a diffusion equation, similar to the electron spin diffusion equation. At the interface between a metal layer (ML) and a magnetic insulator layer (MIL), we show that the spin current of the ML and the magnon current of the MIL are mutually transferable. We introduce a concept of spin convertance [1] that quantitatively measures magnon current induced by electron spin accumulation and spin current generated by magnon accumulation at the interface. With the above formalism, we predict some interesting spin transport phenomena for several layered structures with a MIL. In particular, we anticipate a novel electric drag mediated by magnons: an applied electric current in one ML induces an electric field in the other ML separated by a thick MIL. Our theory also provides a new perspective on the longitudinal spin Seebect effect [2] from the point of view of magnon current driven by the thermal gradient across a MIL. We discuss the dependence of these phenomena on temperature, materials properties, and geometric parameters. \\[4pt] [1] S. S.-L. Zhang and S. Zhang, Phys. Rev. Lett. 109, 096603 (2012); S. S.-L. Zhang and S. Zhang, arXiv:1210.2735v2.\\[0pt] [2] K. Uchida et al., Appl. Phys. Lett. 97, 172505 (2010); H. Adachi and S. Maekawa, arXiv:1209.0228v1. [Preview Abstract] |
Wednesday, March 20, 2013 3:42PM - 4:18PM |
R14.00005: Magnon drag thermopile Invited Speaker: Sergio O. Valenzuela Thermoelectric effects in spintronics are gathering increasing attention as a means of controlling spin information by using heat flow. Thermal magnons (spin-wave quanta) are expected to play a major role, however, the coupling between electrons and magnons in ferromagnetic metals remains poorly understood. We demonstrate a conceptually new device that enables us to gather information on magnon-electron scattering and magnon-drag effects [1]. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon drag thermoelectric effects. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. These results demonstrate the feasibility of directly converting magnon dynamics of nanomagnets into an electrical signal and could pave the way to novel thermoelectric devices for energy harvesting.\\[4pt] [1] M.V. Costache, G.A. Bridoux, I. Neumann and S.O. Valenzuela, Nature Mater. 11, 199 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 4:18PM - 4:30PM |
R14.00006: Theory of Magnon Drag in Ferromagnetic Bilayers Tianyu Liu, Giovanni Vignale, Michael E. Flatt\'e We introduce and study theoretically a novel drag effect that we expect to occur in ferromagnetic bilayer systems. A steady spin-wave (magnon) spin current propagating in one layer (the active layer) induces an inhomogeneous distribution of magnons in the other layer (the passive layer) through the magnetic dipole-dipole interaction. There are significant differences between this effect and the ordinary and well-studied Coulomb drag in electronic bilayers. First, the particles in questions are bosons, and their number is not conserved (this is at variance with systems of bosonic atoms, where number is conserved). Second, it becomes essential to take into account, besides magnon-magnon scattering, processes in which two magnons in one layer merge to produce a magnon in the other, or a magnon in one layer decays producing two magnons in the other. In analogy to the theory of Coulomb drag we calculate the interlayer transport coefficients (relating, for example, the temperature gradient in one layer to the spin current in the other) for different experimental configurations. [Preview Abstract] |
Wednesday, March 20, 2013 4:30PM - 4:42PM |
R14.00007: Thermoelectric detection of spin waves Helmut Schultheiss, John E. Pearson, Samuel D. Bader, Axel Hoffmann We report on the thermoelectric detection of spin waves in permalloy stripes via the anomalous Nernst effect\footnote{H. Schultheiss, J.E. Pearson, S.D. Bader, and A. Hoffmann, Phys. Rev. Lett. in press.}. Spin waves are locally excited by a microwave current flowing in a coplanar waveguide placed on top of a permalloy stripe, which acts as a waveguide for spin waves. Electric contacts at the ends of the permalloy stripe measure a dc voltage generated along the stripe. Magnetic field sweeps for different applied microwave frequencies reveal, with remarkable signal-to-noise, an electric voltage signature characteristic of spin-wave excitations. The symmetry of the signal with respect to the applied magnetic field direction indicates that the anomalous Nernst effect is responsible; Seebeck effects, anisotropic magnetoresistance, and voltages due to spin-motive forces are excluded. The dissipation of spin waves causes local heating, that drains into the substrate giving rise to a temperature gradient perpendicular to the sample plane, resulting in the anomalous Nernst voltage. Since this method is solely based on the heat generation inside the magnetic film due to the relaxation of the magnetization it has practically no lower limit for the wavelength of the detected spin waves. [Preview Abstract] |
Wednesday, March 20, 2013 4:42PM - 4:54PM |
R14.00008: Spin Currents coupling with magnon excitation in Ferromagnetic Insulator Tao Liu, Jiaxi Li, Jianwei Zhang We studied spin currents coupling in two Ferromagnetic/normal metal multilayers which are connected by a Ferromagnetic Insulator(FI) layer(such as YIG). In our modeling, we adopted self-consistent spin dependent Boltzmann equations and magnon Boltzmann equation. When applying an in-plane current in first FM layer, a transverse spin current was generated due to Anomalous Hall effect(AHE), after crossing normal metal layer, this transverse spin current will produce magnon excitation at N/FI interface. With carrying spin information, magnon excitations in FI can eventually excite a new spin current at second F/N interface. Although the FI cannot support any spin current propagation across it, but spin polarization information was passed through FI with propagation of magnon. Finally, the transverse spin current in second FM layer can also generate another in-plane spin current by AHE. Our results showed the spin current in second FM layer can be large as the same order of one in first FM layer at limit case. Through the magnon propagation in FI layer, two spin current circuits were coupled indirectly, i.e.without any charge current exchange. we also showed, when applying a magnetic field on FI layer, spin current in final FM layer can be manipulated by varying magnon excitation. [Preview Abstract] |
Wednesday, March 20, 2013 4:54PM - 5:06PM |
R14.00009: Effect of magnetism on the vibrational properties of the Ni-Cu alloy: a first-principles study Omar De la Pena-Seaman, Ivan Bustamante-Romero, Rolf Heid, Klaus-Peter Bohnen We have studied the lattice dynamical properties of the Ni$_{1-x}$Cu$_x$ magnetic alloy within the framework of density functional perturbation theory, using a mixed-basis pseudopotential method and the virtual crystal approximation for modeling the alloy. The system has been investigated for both non-magnetic (NM) and ferromagnetic (FM) phases. The performance of LDA and GGA exchange-correlation functionals on the properties under study was analyzed. The structural optimization for each magnetic phase, NM and FM, in the full range of concentrations ($0\leq x \leq 1$) was performed. By studying the electronic structure and its evolution as a function of $x$, we determined the FM-NM phase transition at $x \approx 0.45$. The calculated full phonon dispersion for NM and FM phases are compared between each other and with experimental data available in the literature at different concentrations. In addition, a detailed analysis of the force constants average coupling was performed, finding a clear signature of the magnetism effects on the vibrational properties for the Ni-Cu alloy. [Preview Abstract] |
Wednesday, March 20, 2013 5:06PM - 5:18PM |
R14.00010: Thermal Hall effect and Berry curvature of spin waves in magnets Shuichi Murakami, Ryo Matsumoto, Ryuichi Shindou Spin waves (magnons) form band structure similar to electrons, and therefore their geometrical structure in $k$ space can be characterized by Berry curvature. This Berry curvature of spin waves causes various interesting phenomena such as thermal Hall effect [1,2] and topological magnonic crystals [3]. In my presentation, we derive the thermal Hall conductivity for spin waves in generic magnets represented as a bosonic Bogoliubov-de Gennes Hamiltonian. We apply this theory to magnetostatic modes in YIG and evaluate the thermal Hall conductivity for the forward volume-wave mode in YIG. We also discuss the relationship with other previous theories on Hall effect of magnons and other bosons. We also apply our theory to magnets with topological chiral edge modes, and discuss thermal transport for the topological edge modes.\\[4pt] [1] R. Matsumoto, S. Murakami, Phys. Rev. B 84, 184406 (2011).\\[0pt] [2] R. Matsumoto, S. Murakami, Phys. Rev. Lett. 106, 197202 (2011).\\[0pt] [3] R. Shindou et al., arXiv.: 1204.3349. [Preview Abstract] |
Wednesday, March 20, 2013 5:18PM - 5:30PM |
R14.00011: Molecular dynamics, spin dynamics study of phonon-magnon interactions in BCC iron Dilina Perera, David P. Landau, G. Malcolm Stocks, Don Nicholson, Markus Eisenbach, Junqi Yin By combining an atomistic many-body potential (Finnis-Sinclair) with a classical Heisenberg-like spin Hamiltonian, we perform combined molecular and spin dynamics simulations to investigate phonon-magnon interactions in BCC iron. The coupling between atomic and spin degrees of freedom is established via a distance dependent exchange interaction derived from first principles electronic structure calculations. Coupled equations of motion are integrated using a second order Suzuki-Trotter decomposition of the exponential time evolution operator. To investigate the effect of lattice vibrations on spin wave spectrum, we calculate spin-spin and density-density dynamic structure factors S(q, $\omega$), and compare that to the results obtained from pure spin dynamics simulations performed on a rigid lattice. In the presence of lattice vibrations, we observe an additional peak in the longitudinal spin-spin dynamic structure factor which coincides with the peak position in density-density dynanmic structure factor. [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