Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B47: Antiferromagnetic Heterostructures and Magnon DragFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Benjamin Jungfleisch, Argonne National Laboratory Room: 394 |
Monday, March 13, 2017 11:15AM - 11:27AM |
B47.00001: Magnon contributions to thermal conductivity and thermopower in a metallic thin film Devin Wesenberg, Eric Edwards, Justin Shaw, Barry Zink Recent theoretical and experimental work has renewed interest in the role of magnons in the transport and thermoelectric properties of metallic ferromagnets. Magnon Drag is one consequence of the electron-magnon interaction whereby the spin excitations in a magnetic material transfer momentum to the electron system and increase the thermopower. Recent theoretical approaches clarify that magnon drag understandably depends on the Gilbert damping, $\alpha $, present in a given material. [1] The simplest theory predicts a magnon drag thermopower S$_{md}$ that is maximized by reduction of $\alpha $. Here we show that a low-damping metal, such as the Co$_{25}$Fe$_{75}$ alloy thin film [2] that has intrinsic Gilbert damping approaching the 10$^{-4}$ level typically seen only in ferromagnetic insulators, has thermal conductivity that deviates strongly from typical metal films, with a significant peak in thermal conductivity at 225K. This material also has a large deviation from the expected Seebeck coefficient estimated from the alloy's composition and density of states. These results suggest a large contribution from a magnon or spin effect due to the intrinsic low damping of magnetization dynamics in the metal. [1] S. J. Watzman, et al. ``Magnon-drag thermopower and Nernst coefficient in Fe, Co, and Ni.'' PRB 94, 144407 (2016). [2] M. A. W. Schoen, et al. ``Ultra-low magnetic damping of a metallic ferromagnet.'' Nature Physics 12, 839 (2016). [Preview Abstract] |
Monday, March 13, 2017 11:27AM - 11:39AM |
B47.00002: Spin Seebeck effect in bulk composite materials Stephen Boona, Koen Vandaele, Isabel Boona, David McComb, Joseph Heremans To date, the spin Seebeck effect (SSE) has been studied almost exclusively in heterostructures comprised of ferromagnetic insulators capped with metallic thin films, with each component carefully crafted to ensure mutual orthogonality of the relevant interfaces, fields, and fluxes. If the ferromagnetic material is conducting, then the anomalous Nernst effect (ANE) is also present, and the two effects combine to enhance the total transverse thermopower. This talk will present the first demonstration of this exact same phenomenon in bulk materials wherein metallic nanoparticles (Pt or Au) are randomly embedded within a conducting ferromagnet (Ni or MnBi) [1]. These composites allow electrical current to be extracted through their entire volume and thus have lower impedance than thin films, and their forgiving morphology means they can be produced using low cost and scalable techniques. Together, these factors make bulk composites a viable pathway for applying SSE toward thermal energy conversion in devices capable of producing power at the W to kW level. After providing proof-of-concept for SSE in bulk materials, the talk will conclude with an update on recent progress and a discussion of how the effect may be further enhanced. [1] Boona, et al., Nature Commun. [in press] (2016), arXiv:1604.05626 [Preview Abstract] |
Monday, March 13, 2017 11:39AM - 11:51AM |
B47.00003: Thermopower and Anomalous Nernst coefficients of binary ferromagnetic alloys Fe$_{1-x}$Co$_{x}$ and Ni$_{1-x}$Cr$_{x}$ Yuanhua Zheng, Michael Adams, Nicolas Antolin, Wolfgang Windl, Joseph Heremans We report the results of magnon-drag thermopower in binary alloys Fe$_{1-x}$Co$_{x}$ and Ni$_{1-x}$Cr$_{x}$. Fe-Co and Ni-Cr alloys are ferromagnets in which magnons are involved in the transport of electrons and induce an additional thermopower by drag effects. The drag effect increases the thermopower by an order of magnitude. A recently developed theory (1) predicts that magnon drag thermopower of elemental 3-d metals is inversely proportional to the number of s and p electrons while the sign is determined by the sign of the effective mass of majority carriers. Combining this theory with our orbitally-resolved band structure calculation of the DOS of the alloys, we predict a change of sign of the thermopower of the Fe-Co alloys with x, and the magnitude of their thermopower. We synthesize the alloys and measure the temperature dependence of their resistivity, thermopower and Nernst coefficients from 77 to 1000 K. We find that magnon-drag contributes greatly to the thermopower and the predictions about sign are verified experimentally. We further extend our research to Ni$_{1-x}$Cr$_{x}$ alloys. Thermoelectric metals require different device design than conventional materials. Here we propose a thermoelectric combustion chamber. (1) S. J. Watzman, et al. PRB (2016). [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:27PM |
B47.00004: Novel contributions to the magnon drag thermopower in metal spintronics Invited Speaker: Benedetta Flebus Metallic ferromagnets subjected to a temperature gradient exhibit a magnonic drag of the electric current, which has been recently shown to dominate the thermopower of elemental iron and copper over a broad range of temperatures. We address this problem by solving a stochastic Landau-Lifshitz equation to calculate the magnon-drag thermopower. The long-wavelength magnetic dynamics result in two contributions to the electromotive force acting on electrons: (1) An adiabatic Berry-phase force related to the solid angle subtended by the magnetic precession and (2) a dissipative correction thereof, which is rooted microscopically in the spin-dephasing scattering. The first contribution results in a net force pushing the electrons towards the hot side, while the second contribution drags electrons towards the cold side, i.e., in the direction of the magnonic drift. The ratio between the two forces is proportional to the ratio between the Gilbert damping coefficient $\alpha$ and the coefficient $\beta$ parametrizing the dissipative contribution to the electromotive force. [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 12:39PM |
B47.00005: Abstract Withdrawn
|
Monday, March 13, 2017 12:39PM - 12:51PM |
B47.00006: Manipulations of inverse spin Hall effect in a FM/Pt/FM trilayer structure via RKKY interlayer interaction Haoliang Liu, Dali Sun, Chuang Zhang, Matthew Groesbeck, Ryan Mclaughlin, Valy Vardeny We studied the inverse spin Hall effect (ISHE), ferromagnetic resonance and MOKE response in FM/NM/FM trilayer (NiFe/Pt/Co) as a function of the Pt layer thickness, d. We found evidence that non-local magnon drag influences the ISHE response in the Pt layer via the RKKY interaction, where the exchange coupling constant oscillates between parallel and antiparallel FM magnetization configuration as a function of d. In particular the ISHE response in the parallel FM configuration was found to be four times larger than that in the conventional Co/Pt or NiFe/Pt bilayer structures. [Preview Abstract] |
Monday, March 13, 2017 12:51PM - 1:27PM |
B47.00007: Spin transport in antiferromagnetic heterostructures Invited Speaker: Kai Chen Recently, it has been demonstrated that antiferromagnetic (AF) insulators are capable of conducting spin current injected by spin pumping and spin Seebeck effect from an adjacent ferromagnetic layer [1]. More importantly, the insertion of thin NiO film between YIG and Pt layer enhances the spin pumping/Seebeck current in the Pt layer. Motivated by such findings, we proposed a theoretical model where the spin current in antiferromagnetic insulators is carried by incoherent thermal magnons. In equilibrium, spin up and spin down magnons in AF materials are equally occupied. While non-equilibrium spin accumulation can be built up when AF magnons from one branch are selectively excited by spin accumulation from an adjacent layer. Then a spin current traverses the AFI layer via magnon spin diffusion. Utilizing spin convertance at interfaces and spin diffusion in each layer, we calculate spin Seebeck current across various layered structures at different temperatures. We find the presence of a NiO film blocks the spin current at low temperature while enhances the spin current at high temperature. The enhancement factor reaches maximum value near the magnetic transition temperature of NiO. The calculated temperature dependence quantitatively agrees with experiments [2]. In contrary, other models in which the spin current is carried by coherent magnons or spin supercurrent predict temperature insensitive spin conductivity of an AF insulator. Furthermore, we investigate the interplay between AF order dynamics and the magnon excitations based on the conversion between incoherent and coherent AF magnons. I am grateful for W. Lin and C.-L. Chien from Johns Hopkins University for their contributions to this work. [1] H. Wang \textit{et al.}, Phys. Rev. Lett. \textbf{113},097202 (2014); W. Lin \textit{et al.}, Phys. Rev. Lett. \textbf{116}, 186601 (2016). [2] K. Chen \textit{et al.}, Phys. Rev. B \textbf{94}, 054413 (2016). [Preview Abstract] |
Monday, March 13, 2017 1:27PM - 1:39PM |
B47.00008: Spin transport through native nickel and nickel-iron oxides Barry Zink, Michael Manno, O'Brien Liam, Johannes Lotze, Mathias Weiler, Devin Wesenberg, Sebastian Goennenwein, Melissa Johnson, Alex Hojem, Chris Leighton Recent reports from our group and others have shown that spin transport is possible through a much wider range of materials than previously thought. These include studies of spin transport, and possible enhancement of spin flow, through very thin nickel oxide and other nominally antiferromagnetic layers inserted between ferromagnets and Pt layers. In this talk we present results of spin transport experiments showing that while the presence of a nonmagnetic oxide at the interface suppresses spin transport from the ferromagnet to the nonmagnetic metal, a thin magnetic oxide (here the native oxide formed on both Py and Ni) enhances the product of the spin-mixing conductance and the spin Hall angle.[1] We also observe clear evidence of an out-of-plane component of magnetic anisotropy in Ni/Pt samples that is enhanced in the presence of the native oxide, resulting in perpendicular exchange bias. The results clarify that spin transport occurs in the oxide despite the lack of long range order at the temperature of the measurements.[1] B. L. Zink et al, PRB v. 93 184401 (2016) [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 1:51PM |
B47.00009: Thermal spin current generation and spin transport in Pt/magnetic-insulator/Py heterostructures Ching-Tzu Chen, Christopher Safranski, Ilya Krivorotov, Jonathan Sun Magnetic insulators can transmit spin current via magnon propagation while blocking charge current. Furthermore, under Joule heating, magnon flow as a result of the spin Seeback effect can generate additional spin current. Incorporating magnetic insulators in a spin-orbit torque magnetoresistive memory device can potentially yield high switching efficiencies. Here we report the DC magneto-transport studies of these two effects in Pt/magnetic-insulator/Py heterostructures, using ferrimagnetic CoFexOy (CFO) and antiferromagnet NiO as the model magnetic insulators. We observe the presence and absence of the inverse spin-Hall signals from the thermal spin current in Pt/CFO/Py and Pt/NiO/Py structures. These results are consistent with our spin-torque FMR linewidths in comparison. We will also report investigations into the magnetic field-angle dependence of these observations. [Preview Abstract] |
Monday, March 13, 2017 1:51PM - 2:03PM |
B47.00010: Spin-Mechanical Inertia in Antiferromagnet Ran Cheng, Xiaochuan Wu, Di Xiao Interplay between spin dynamics and mechanical motions is responsible for numerous striking phenomena, which has shaped a rapidly expanding field known as spin-mechanics. The guiding principle of this field has been the conservation of angular momentum that involves both quantum spins and classical mechanical rotations. However, in an antiferromagnet, the macroscopic magnetization vanishes while the order parameter (N\'{e}el order) does not carry an angular momentum. It is therefore not clear whether the order parameter dynamics has any mechanical consequence as its ferromagnetic counterparts. Here we demonstrate that the N\'{e}el order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperature when magnon excitations are considered. Such a spin-mechanical inertia can produce measurable consequences at nanometer scales. Our discovery establishes spin-mechanical inertia as an essential ingredient to properly describe spin-mechanical effects in AFs, which supplements the known governing physics from angular momentum conservation. [Preview Abstract] |
Monday, March 13, 2017 2:03PM - 2:15PM |
B47.00011: Magnon mediated anomalous responses of magnetic systems Vladimir Zyuzin, Alexey Kovalev In this talk various anomalous transport properties of ordered insulating magnets will be covered. We will first focus on magnon spin Nernst effects in ferromagnet and antiferromagnet systems. Second, magnetization dynamics driven magnon spin Hall and thermal Hall effects will be discussed. In both cases the effects are driven by non-trivial topology of magnon energy bands and Dzyaloshinskii-Moriya interaction. To demonstrate the effects we will use honeycomb lattice magnetic system, and a toy model of Weyl magnons based on a system of stacked honeycomb magnets. ~ ~ [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