Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X22: Spin-Orbit Effects at Metal/Insulator InterfacesFocus Session
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Sponsoring Units: GMAG DMP FIAP Chair: Can Onur Avci, Massachusetts Institute of Technology-MIT Room: LACC 402A |
Friday, March 9, 2018 8:00AM - 8:12AM |
X22.00001: Magnetic avalanche dynamics in a model insulating Ising magnet Daniel Silevitch, Christopher Tang, Jian Xu, Thomas Rosenbaum The dynamics and energetics of the domain reversal process in ferromagnets has been extensively studied through the mechanism of Barkhausen noise, where individual switching events generate experimentally-detectable avalanches. As the great majority of ferromagnetic materials are metallic, such switching events are typically accompanied by induced eddy currents which act as a drag force on the magnetic avalanches. Whether eddy-current drag dominates the dynamics is an important open question. We address this question by performing Barkhausen measurements on the model Ising system LiHo0.65Y0.35F4, an insulating rare-earth, dipole-coupled ferromagnet with a Curie temperature of 0.980 K. We find symmetrical scaled distributions near the Curie temperature, indicative of a drag-free environment. By contrast, strong asymmetries appear for long-duration events at lower temperatures, suggesting the presence of drag even in the absence of eddy currents. |
Friday, March 9, 2018 8:12AM - 8:24AM |
X22.00002: Enhancement of spin-wave propagation using topological insulators Aryan Navabi, Yuxiang Liu, Pramey Upadhyaya, Farbod Ebrahimi, Guoqiang Yu, Koichi Murata, Lei Pan, Pedram Khalili Amiri, Yaroslav Tserkovnyak, Kang Wang Spin-wave damping in planar Yttrium Iron Garnet (YIG) films remains the main drawback in integrating ferromagnetic films with Radio Frequency Integrated Circuits. Most studies have often used Pt as a source of spin current through the spin Hall effect to provide an anti-damping torque. Apart from Pt and other heavy metals, another class of materials that can also be used are topological insulators (TI) where the current at the surface is spin polarized. Therefore, YIG/TI has great potential to enhance spin-wave propagation in ferromagnetic materials. |
Friday, March 9, 2018 8:24AM - 8:36AM |
X22.00003: Nonreciprocal Spin Wave Propagation in a Thin YIG Film for an in-Plane Magnetization Jonathan Trossman, Jinho Lim, Wonbae Bang, C.C. Tsai, S-j Lee, J Ketterson We report measurements on the magnetic field dependence of the wavevector of spin waves of a given frequency propagating in a 3μm YIG film for an in-plane magnetic field. Waves are transmitted and received from opposing but parallel edges of a rectangular platelet using 50μm wire antennas adjacent to the edges and detected using a phase-sensitive method. Both the Damon-Eshbach (DE) and backward volume (BV) modes are observed, together with their dependence on the in-plane magnetic field direction, as measured relative to the propagation direction. Measurements are performed in a variety of configurations including YIG/GGG, Cu/Air/YIG/GGG, Cu/YIG/GGG, and Pt/YIG/GGG and are performed for both positive and negative fields and for forward and backward propagation relative to a given field direction. Data are fully reproduced only when both the magnetic field and the propagation direction (the wavevector) are reversed (double reversal); data obtained when only one of these (field or wavevector) is reversed generally do not reproduce. The difference is largest for the DE mode, in agreement with earlier theoretical predictions. |
Friday, March 9, 2018 8:36AM - 9:12AM |
X22.00004: Anomalous Current-Induced Spin-Orbit Torques in Ferrimagnets Invited Speaker: Hyunsoo Yang Spin-orbit torques (SOTs) have been recently studied for its potential applications in memory and logic devices, mostly with ferromagnetic thin films. As the cell size shrinks, these ferromagnetic thin films are thermally unstable due to their sub nano-meter thicknesses. We study SOT-induced magnetization switching and effective fields in rare earth-transition metal (RE-TM) ferrimagnet alloy films and multilayers. We show that devices from the structure of heavy metal/ferrimagnet present a huge switching efficiency and maximum spin-orbit effective fields. It is observed that the switching efficiency and SOT effective fields increase by one order of magnitude as the ferrimagnet approaches compensation. This anomalous increase of the switching efficiency and SOT effective fields is attributed to the negative exchange interaction field due to the antiferromagnetic ordering between the Co and Gd sub-lattices. The negative exchange interaction makes the ferrimagnet thermally stable near compensation by increasing its anisotropy and also provides the exchange coupling torque that assists in switching, effectively increasing the overall switching efficiency of ferrimagnetic SOT devices. We also show that the SOT in the Co/Tb ferrimagnet system increases with the ferrimagnet thickness. The SOT effective fields and the switching efficiency in Co/Tb are about one order magnitude larger than that of ferromagnets. Our results trigger a ferrimagnet as a core building block in spintronics. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X22.00005: Measurements of the long-wavelength dispersion of spin waves along the principal directions of an yttrium iron garnet film Jinho Lim, Wonbae Bang, Jonathan Trossman, Dovran Amanov, Matthias Benjamin Jungfleisch, Axel Hoffmann, J Ketterson Historically, spin waves have been excited by two techniques: 1) a wire, stripe, or coaxial stripline [1] (which provides weak coupling but functions over a range of wavelengths that is of the order of or larger than the characteristic width dimensions of the stripes), or 2) a spatially-resonant multi-element antenna [2]. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X22.00006: Spin-dependent transport properties in Pt/Fe-phthalocyanine metal-organic bilayer Koki SHIMOSE, Takeshi Kawabe, Minori Goto, Yoshishige Suzuki, Shinji Miwa Metal-phthalocyanine complexes have been explored for their application in spintronics because of its unique magnetic properties [1]. However, investigation of the magnetic properties in phthalocyanines have been done with localized techniques such as scanning probe microscopy, and there have been few reports employing electric conduction in devices [2]. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X22.00007: A Magnetometer Based on a Spin Wave Interferometer Michael Balinskiy, David Gutierrez, Howard Chiang, Alexander Kozhevnikov, Galina Dudko, Yuri Filimonov, Alexander Balandin, Alexander Khitun We describe a magnetic field sensor based on a spin wave interferometer. Its sensing element consists of a magnetic cross junction with four micro-antennas fabricated at the edges. Two of these antennas are used for spin wave excitation while two other antennas are used for detection of the inductive voltage produced by the interfering spin waves. The sensitivity attains its maximum under the destructive interference condition. We report experimental data obtained for a micrometer scale Y3Fe2(FeO4)3 cross structure. The change of the inductive voltage near the destructive interference point exceeds 40 dB per 1 Oe. The phase of the output signal exhibits a π-phase shift within 1 Oe. The data are collected at room temperature. Taking into account the low thermal noise in ferrite structures, we estimate that the maximum sensitivity of the spin wave magnetometer may exceed attotesla. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X22.00008: Perovskite oxides for spin pumping Samuel Crossley, Adrian Swartz, Kazunori Nishio, Yasuyuki Hikita, Harold Hwang Resonant excitation of magnetic films is an attractive source of pure spin current for spintronics applications. Exploiting this spin pumping effect in heterostructures of transition metal oxides, with tunable spin-charge-orbital degrees of freedom, could lead to novel physical probes of these materials and new operational regimes for spintronics devices. Atomically precise interfaces are now readily obtained, which could help advance understanding of interfacial spin transport. Using pulsed laser deposition, we have fabricated heterostructures of epitaxial oxides incorporating candidate high-spin orbit materials, in order to understand the potential phase space for interfacial spin transport in oxide materials. One promising group is the Ruddlesden-Popper series of perovskite iridates, which can now be thermodynamically stabilized in the ultrathin limit. Metallic Co, Cu and Pt have been incorporated into our samples by electron beam evaporation performed in-situ, without breaking vacuum. We will report our results on ferromagnetic resonance, damping and magnetic anisotropy. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X22.00009: Anomalous Hall conductivity of antiperovskite GaNMn3 Gautam Gurung, Ding-Fu Shao, Tula Paudel, Evgeny Tsymbal The interplay between lattice, charge, and spin degree of freedom in antiperovskite compounds gives rise to a range of functional properties including those interesting for spintronics applications. In particular, GaNMn3 has garnered attention due to possibility of tuning the magnetic phases, such as non-collinear antiferromagnetic Γ5g phase and collinear ferrimagnetic M-1 phase, by chemical doping and hydrostatic pressure. Here, using first-principles density-functional theory calculations, we explore the anomalous Hall conductivity of antiperovskite GaNMn3 in different magnetic configurations. In the ferromagnetic M-1 phase, to the anomalous Hall conductivity emerges due to the broken time reversal symmetry, whereas in the non-collinear antiferromagnetic Γ5g phase with zero magnetization the anomalous Hall conductivity results from the broken time reversal/mirror reflection symmetry combination. We calculate the magnitude of the anomalous Hall conductivity in both phases and discuss the underlying physics associated with this phenomenon. |
Friday, March 9, 2018 10:12AM - 10:24AM |
X22.00010: Electromagnetic Wave Propagation in Asymmetric Hyperbolic Magnetic Media Rair Macedo, Robert Stamps Natural hyperbolic magnetic media exist in which optical effects such Goos-Hanchen shifts [1] and negative reflection [2] can be tuned by simply applying external magnetic fields. We discuss how this occurs in antiferromagnets and show that by rotating the easy axis of the crystal, the hyperbolic dispersion is rotated and the angle of refraction is modified and cannot be defined as simply negative and positive as it is done in conventional hyperbolic media. The optical properties (i.e. focusing) derived from the hyperbolic behaviour are also modified. Because the crystal is magnetic all afore mentioned behaviour can be tuned to a different frequency by applying external magnetic fields. |
Friday, March 9, 2018 10:24AM - 10:36AM |
X22.00011: Generalized spin-transfer torque and collective spin dynamics in disordered magnets Hector Ochoa, Yaroslav Tserkovnyak We provide a generalized theory of spin transfer and reciprocal pumping effects at interfaces between metals and non-collinear magnets, including the cases of spin glasses and amorphous magnets. The theory is based on energetics rather than spin conservation, albeit the latter is recovered in the appropriate language. The generalized spin-mixing conductance tensor is parametrized by three coefficients, corresponding to the three independent generators of spin rotations. In the limit of exchange-dominated interactions, those correspond to the soft modes of the macroscopic, coarse-grained dynamics, restoring the fully broken rotational symmetry. We employ this formalism to demonstrate that disordered magnets represent a very versatile platform for spin transport, sustaining long-range drag signals between metal contacts even in the presence of damping sources. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X22.00012: Topological magnon bands in antiferromagnetic systems with honeycomb lattice Ki Hoon Lee, Kisoo Park, Je-Guen Park, Suk Bum Chung We present the topological property of magnon bands in the collinear magnetic orders for the antiferromagnetic honeycomb lattice. We investigated the linear spin waves of zigzag and stripy phases. Berry curvature and symmetry constraints on magnon band structure are identified. For both zigzag and stripy phases, we found that spatial mirror symmetry protects gapless points in the magnon bands, which can be removed by additional Dzyaloshinskii-Moriya (DM) term. In the zigzag phase, a non-symmorphic symmetry gives rise to two-(four-)degeneracy at the zone boundary with (without) spin anisotropy, preventing the disentanglement of the magnon bands. In contrast, the magnon bands of the stripy phase can be disentangled with a finite DM term, leaving each band with a non-zero Chern number. We have also studied the spin Nernst property. Our study establishes the existence of the non-trivial magnon band topology for all observed collinear antiferromagnetic honeycomb lattice in the presence of the DM term. |
Friday, March 9, 2018 10:48AM - 11:00AM |
X22.00013: Impact of the magnetic sublattice configuration on the Spin-Hall Magnetoresistance Nynke Vlietstra, Kathrin Ganzhorn, Johanna Fischer, Matthias Althammer, Hans Huebl, Matthias Opel, Stephan Geprägs, Sebastian Goennenwein, Rudolf Gross Recently, the ferrimagnetic insulating yttrium iron garnet (YIG) has been studied mostly in combination with an adjacent few-nm-thick platinum (Pt) layer. These studies lead to the discovery of a novel spintronic effect, called the spin-Hall magnetoresistance (SMR)[1,2]. |
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