Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F22: Spin Transport, Spin Logic and Spin MemoriesFocus
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Sponsoring Units: GMAG DMP FIAP Chair: Alina DEAC, Helmholtz-Zentrum Dresden-Rossendorf Room: LACC 402A |
Tuesday, March 6, 2018 11:15AM - 11:27AM |
F22.00001: Enhancement of Spin Injection in Metallic Nonlocal Spin Valves on Silicon Nitride Membranes Rachel Bennet, Alex Hojem, Devin Wesenberg, Barry Zink Nonlocal spin valves (NLSVs) are an important tool for both applied and fundamental research in nanomagnetism due to their unique ability to separate charge and spin currents.[1,2] Previous research shows that changes to the composition of the NLSV substrate can have a marked effect on the background nonlocal resistance by changing the substrate thermal conductance,[3] and our research demonstrates enhancement of nonlocal spin resistance by the anomalous Nernst effect (ANE).[4] |
Tuesday, March 6, 2018 11:27AM - 11:39AM |
F22.00002: Spin Transport in Ferromagnet/Superconductor Spin Valves Evan Moen, Oriol Valls We consider spin transport in Ferromagnetic/Superconductor spin valves. These are heterogeneous layered structures including F1 / N / F2 / S where F1 and F2 are ferromagnets, S is a superconductor, and N is a normal metal spacer used in actual devices. We use fully self consistent microscopic methods that ensure that the proper relations between spin current and spin transfer torque (STT) are satisfied. We include realistic geometric and material parameter values and interfacial scattering. We obtain results for the spin current and STT as functions of position within the heterostructure, for all magnetic misalignment angles φ between the F1 and F2 layers. We do this for multiple applied bias values. Furthermore, we consider the average torque and spin accumulation of each layer as a function of the bias. We discuss the dependence of our results on the above parameters. |
Tuesday, March 6, 2018 11:39AM - 11:51AM |
F22.00003: Pulsed Spin Torque Switching of Spin-Valves with Dilute Permalloy Free Layers for Cryogenic Applications Laura Rehm, Volker Sluka, Christian Hahn, Graham Rowlands, Thomas Ohki, Andrew Kent Cryogenic spin-transfer spin-valve (CST-SV) devices are considered a potential solution for low-temperature data storage in superconducting computing, due to their low impedance and power consumption, their high speed and large packing density. These devices incorporate Nb electrodes with a synthetic antiferromagnetic reference layer and a Cu-diluted Permalloy (Py) free layer with reduced magnetic moment density, designed to reduce the switching energy. Specifically, we studied 50 nm x 110 nm elliptically shaped in-plane magnetized nanopillars. Quasistatic current-voltage measurements of these devices show a factor of two reduction of average switching currents compared to devices with an undiluted Py free layer, while exhibiting a similar resistance difference between the parallel (P) and antiparallel (AP) magnetic configurations of about 200 mΩ. Both types of devices show sharp switching with coercive fields in the range of 10-40 mT. Using a cryogenic probe station, we investigated pulsed switching with pulses from 0.1 ns to 100 ms and compare the characteristics of undiluted versus diluted Py free layers, including the effective energy barrier heights and their temperature dependence. |
Tuesday, March 6, 2018 11:51AM - 12:03PM |
F22.00004: Microscopic origin of voltage-controlled magnetic anisotropy in FePt/MgO epitaxial multilayer Shinji Miwa, Motohiro Suzuki, Masahito Tsujikawa, Takayuki Nozaki, Minori Goto, Yoshinori Kotani, Tadakatsu Ohkubo, Eiiti Tamura, Frederic Bonell, Kazuhiro Hono, Tetsuya Nakamura, Masafumi Shirai, Yoshishige Suzuki Spin-transfer has surpassed current-induced magnetic fields as the preferred technology for magnetization switching in nanoscale magnets. However, spin-transfer switching exhibits Joule heating that remains too large to ignore. Thus, a novel method offering magnetization control without electric current is highly desirable. Because voltage-controlled magnetic anisotropy (VCMA) in Fe/MgO-based devices [1] can be an ultimate technology for spintronics devices, a novel method to increase the VCMA is important. |
Tuesday, March 6, 2018 12:03PM - 12:15PM |
F22.00005: Electric-field-induced changes in magnetic moments and magnetic anisotropy in Co/MgO multilayer Takeshi Kawabe, Kohei Yoshikawa, Masahito Tsujikawa, Takuya Tsukahara, Kohei Nawaoka, Yoshinori Kotani, Kentaro Toyoki, Minori Goto, Motohiro Suzuki, Tetsuya Nakamura, Masafumi Shirai, Yoshishige Suzuki, Shinji Miwa Voltage controlled magnetic anisotropy (VCMA) in Fe/MgO-based devices has been intensively studied [1]. One explanation for the VCMA is an induced change in orbital magnetic moment. However, electric field induced changes in orbital magnetic moment has never been confirmed experimentally. It has recently been pointed out the significance of the magnetic dipole Tz term to the VCMA in Pt with proximity-induced spin polarization [2]. In a Fe/Pt/MgO, the Tz term induction, correlating with electric quadrupole induction, induces a VCMA. |
Tuesday, March 6, 2018 12:15PM - 12:27PM |
F22.00006: Role of external electric field and spin-orbit coupling in magneto-transport properties at ferromagnetic metal/MgO interfaces Kohji Nakamura, Abdul-Muizz Pradipto, Shunta Ando, Toru Akiyama, Tomonori Ito, Michael Weinert Electric-field (E-field) induced modification of magnetism in transition-metal thin-films has been shown as a potential approach offering the promising pathway to control magnetism. Previously, we have investigated the E-field induced modification of the magnetocrystalline anisotropy (MCA) at an Fe/MgO interface and at that with an insertion of heavy-metals from first-principles.[1] We here extend the investigation to magneto-transport properties in an E-field. Calculations were carried out using the FLAPW method in which the conductivity tensor was obtained by applying the linear response theory. By insertion of heavy metals of 5d (Os, Ir, Pt) at the Fe/MgO interface, we find that the E-field induced MCA modification is dramatically improved. On the other hands, the tunneling magnetoresistance ratio decreases upon the insertion, where the reduction may be explained by the exchange splitting and SOC strength of the insertion elements. The anomalous/spin Hall conductivities are furthermore found to modified by an application of E-field. [1] K. Nakamura, et.al., PRB 81, 220409R (2010); JMMM 429, 214 (2017). |
Tuesday, March 6, 2018 12:27PM - 12:39PM |
F22.00007: Controlling nanosecond spin-orbit torque switching of three terminal magnetic tunnel junctions with geometry Shengjie Shi, Dan Ralph, Robert Buhrman Recently we reported that a significant reduction of critical switching current Ic can be achieved in tungsten based three-terminal magnetic tunnel junctions with atomic Hf layer modification of the interfaces. This has stimulated additional work to further optimize these nanoscale structures to achieve still lower critical currents and higher speed switching for future cache memory applications. Here we report on a systematic study of the micromagnetic factors that determine both the intrinsic time scale of this nanosecond switching behavior and the degree of symmetry between the fast switching from parallel (P) to anti-parallel (AP) and the reverse. Using a modified geometry of the nanopillar magnetic tunnel junction structure we find that we are able to tune the relative speeds of reversal between two polarities. We have also designed a new spin Hall channel geometry to achieve a major reduction in channel resistance. This enables us to examine write error rates in the very high pulse current regime, I >> Ic . The results of these studies further demonstrate the feasibility of this type of three-terminal spin-orbit torque device as a high speed, energy efficient, non-volatile memory solution. |
Tuesday, March 6, 2018 12:39PM - 12:51PM |
F22.00008: Exchange-Mediated Rotation Coherence in Magnetostrictive / Non-Magnetostrictive Strain-Coupled Multiferroics Michelle Jamer, Colin Rementer, Anthony Barra, Greg Carman, Alexander Grutter, Daniel Gopman, Brian Kirby, Julie Borchers, Jane Chang Multiferroics are widely pursued, as such materials offer a multitude of exciting new device applications. There is a push to develop artificial composite multiferroics since there are few examples of natural multiferroics with room temperature functionality.[1] For strain-coupled multiferroics, voltage control of ferromagnetism can be achieved by interfacing piezoelectric and magnetostrictive materials. Functionality can be extended by exchange coupling the magnetostrictive material to a non-magnetostrictive magnet. Interfacing magnetostrictive Galfenol (Fe100-xGax; x=15-25) with low loss Permalloy (Ni80Fe20) on a PMN-PT substrate results in a strain-coupled system with the potential for quick-switching for high frequency applications. Polarized neutron reflectometry (PNR) was used to measure the electric field dependencies of the structural and magnetic depth profiles for a series of Ni80Fe20 / Fe100-xGax bilayers, and Fe100-xGax / Ni80Fe20 multilayer, grown on PMN-PT. These results are consistent with micromagnetic simulations which suggest a 5% deviation in rotation angle across the entire Fe100-xGax and Ni80Fe20 stack. Thus, we demonstrate coherent electric field response across tens of nm - an optimal range for device applications. |
Tuesday, March 6, 2018 12:51PM - 1:03PM |
F22.00009: Reciprocity in diffusive spin-current circuits Yaroslaw Bazaliy, Revaz Ramazashvili Similarly to their purely electric counterparts, spintronic circuits are made of lumped elements connected into a network. Spin and charge currents flowing into each element are described by its matrix conductance. We establish a reciprocity relation between the entries of the conductance matrix of a diffusive multi-terminal linear element. In particular, reciprocity equates the spin transmission through a two-terminal element in the forward and backwards directions. Its application to “geometric spin ratchets” shows that their directional shape does not result in preferential transmission of spin in a certain direction. |
Tuesday, March 6, 2018 1:03PM - 1:39PM |
F22.00010: How nanosecond magnetization dynamics during spin-Hall switching of in-plane MTJs enables a cryogenic memory cell with superconducting line drivers Invited Speaker: Graham Rowlands A scarcity of advantageous thermal fluctuations typically prevents magnetization reversal of in-plane magnetic memory elements from being both fast and reliable, a problem that is only exacerbated at lower temperatures. We show that three-terminal spin-Hall effect (SHE) memories are not subject to such constraints. By virtue of the combined action of spin-torque and an Oersted field torque from the metallic write channel, these devices can be driven at fast switching times (< 1-2 ns) and low error rates ( < 10-6) that persist down to T=4 K. |
Tuesday, March 6, 2018 1:39PM - 1:51PM |
F22.00011: Thermally Reliable Magnetostriction-Assisted All-Spin Domino-Logic Device Rouhollah Mousavi Iraei, Dmitri Nikonov, Ian Young, Sasikanth Manipatruni, Azad Naeemi Recently, researchers have experimentally demonstrated the energy efficient 900 voltage-mediated magnetic reorientation through changing the magnetoelastic energy, which couples the strain to the magnetization. We present a magnetic-piezoelectric heterostructure that utilizes 900 magnetostrictive switching and 900 spin-transfer torque (STT) switching to perform magnetization reversal. The device relies on the switching from the saddle point of energy profile, demonstrated to be more delay and energy efficient and robust to thermal noise. The operation and the physics of the device are studied to benchmark its performance against other spintronic and CMOS devices. Compared to the all-spin logic device, the proposed device has achieved 14× shorter delay and 19× lower energy dissipation for implementation of a 32-bit arithmetic-logic unit, while maintaining low-voltage operation, non-reciprocity, non-volatility, cascadability, and thermal reliability. Moreover, several magnetic and piezoelectric materials are studied to investigate the best candidate materials to implement the proposed device. |
Tuesday, March 6, 2018 1:51PM - 2:03PM |
F22.00012: Minimization of Switching Energy in Scaledown of Nanomagnetic Devices in Fokker-Planck Approach Ella Gale, Ilyas Farhat, A. Isakovic Minimization of energy needed for switching of nanomagnetic devices, such as magnetic tunnel junctions (MTJ) and spin nanotorque oscillators (SNTO) is performed, relying on the procedure we developed based on Fokker-Planck approach, initiated in references [1, 2]. The procedure accounts for the controllable inducement of the interfacial anisotropy between at least one pair of the neighboring layers of the MTJ or SNTO [3], and takes into account that at least two geometric parameters of a nanomagnetic devices are affected by the scaledown. Modeling strongly suggests existence of an optimal effective anisotropy field (that is, optimal value for minimized switching energy or current), Hkeff, which changes for a selected set of geometric scaledown parameters. The influence of the effective anisotropy field is studied in both switching regimes, (I < Ic, I > Ic). Energy density changes are calculated for various nanomagnetic device design parameters, as are the variations of the switching rate. |
Tuesday, March 6, 2018 2:03PM - 2:15PM |
F22.00013: Large Anomalous Hall Current in a Topological Ferromagnetic Van Der Waals Material Kyoo Kim, Junho Seo, Eunwoo Lee, Jong Mok Ok, Jin Won Lee, Y. J. Jo, Woun Kang, Ji Hoon Shim, Han Woong Yeom, Byung Min, Bohm-Jung Yang, Jun Sung Kim Two-dimensional van der Waals materials have shown interesting spin-related properties and promise for spintronic applications. Up to now, however, most of the studies on vdW materials has been focused on non-magnetic materials because magnetic vdW materials are relatively rare. Here we report the large anomalous Hall effect of a metallic ferromagnetic vdW material Fe3GeTe2, which has the highest Curie temperature of Tc ~ 220 K among FM vdW materials. In this system, large Berry curvature in the momentum space is induced by topological nodal lines, which is protected by crystalline symmetries. This turns out to make Fe3GeTe2 having the largest anomalous Hall angle and anomalous Hall factor among metallic ferromagnets, demonstrating its great potential for various spin and orbital-dependent electronic functionalities. |
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