Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P21: New Materials and Devices for Spin LogicFocus
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Christianne Beekman, Florida State Univ Room: LACC 309 |
Wednesday, March 7, 2018 2:30PM - 3:06PM |
P21.00001: Material Targets and Challenges in Realizing Spintronics for Computing Invited Speaker: Ian Young Continued technology scaling of integrated circuits according to the Moore’s law may be achieved via gradual introduction of new materials and state variables [1]. In particular, for spin based computing and memory, novel materials and devices are essential to meet the demands of on chip memory as well as logic [2]. Over the past ten years invention of logic devices has occurred that are based upon spin transfer torque (all-spin logic - ASL, spin torque majority gate - STMG) or magneto-electric effect (magneto-electric majority gate – MEMG, spin wave device – SWD, and magneto-electric spin-orbit logic – MESO [3]). While the switching speed of spintronic logic devices is slower than CMOS devices, the switching energy is lower. Therefore spin logic can provide comparable computational throughput in power limited cases. Also its non-volatility has the potential to enable always-off, instantly-on computing. This drives the research for improved spin and magnetism in materials and interfaces. [1] Nikonov, D.E.; Young, I.A., "Benchmarking of Beyond-CMOS Exploratory Devices for Logic Integrated Circuits," in Exploratory Solid-State Computational Devices and Circuits, IEEE Journal on , vol.1, no., pp.3- 11, Dec. 2015. [2] S. Manipatruni, D. E. Nikonov, and I. A. Young, “Material Targets for Scaling All-Spin Logic”, Phys. Rev. Applied 5, 014002 (2016). [3] Manipatruni, Sasikanth, Dmitri E. Nikonov, and Ian A. Young. "Spin-orbit logic with magnetoelectric nodes: A scalable charge mediated nonvolatile spintronic logic." arXiv preprint arXiv:1512.05428 (2015). |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P21.00002: Magnetic properties of InP wurtzite nanowires from theory: g-factors and exciton Zeeman splitting Paulo Faria Junior, Davide Tedeschi, Marta De Luca, Benedikt Scharf, Antonio Polimeni, Jaroslav Fabian Spin-dependent phenomena in III-V wurtzite (WZ) semiconductor nanowires (NWs) have recently attracted great attention. For instance, recent experiments showed that InP WZ NWs exhibit an unconventional and unexplained nonlinear Zeeman splitting (ZS) under high magnetic fields[1,2]. Starting with a robust k.p Hamiltonian[3], we investigate the magnetic properties of InP in the WZ phase, specifically focusing on g-factors and excitonic ZS. Our calculated values of effective g-factors are in excellent agreement with experimental data[1,2] and also show the independent contributions of electron and hole g-factors, typically entangled in experiments due to excitonic effects. Regarding the nonlinear ZS of excitons in large magnetic fields, we showed that the origin for such nonlinearity is the interaction between heavy and light hole bands with spin up from different Landau level indices[2,4]. [1] De Luca et al., Nano Lett. 14, 4250 (2014). [2] Tedeschi et al., in preparation. [3] Faria Junior et al., PRB 93, 235204 (2016). [4] Faria Junior et al., in preparation. |
Wednesday, March 7, 2018 3:18PM - 3:30PM |
P21.00003: Large current modulation in a GaMnAs-based vertical spin metal-oxide-semiconductor field-effect transistor Toshiki Kanaki, Hiroki Yamasaki, Tomohiro Koyama, Daichi Chiba, Shinobu Ohya, Masaaki Tanaka A spin MOSFET is one of the most promising devices for the post-scaling era [1]. Recently, we reported large MR ratios (60%[2] and 5%[3]) in GaMnAs-based vertical spin FETs, which are much larger than those reported in planar spin MOSFETs (~0.1%) [4–6]. However, the present most important challenge for the practical application of the vertical spin FETs is to improve the small current modulation ratios, which are ~20% at most [3]. Here, we present a vertical spin MOSFET exhibiting a large current modulation ratio up to 130%, which is the largest value in vertical spin FETs reported thus far. Comparing the experimental data with calculated results, the electric-field effect on the indirect tunneling current via defect states in the GaAs channel layer is the most probable origin for the large modulation ratio. |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P21.00004: Growth, structure, and physical properties of CeAlGe and CeAlSi single crystals Halyna Hodovanets, Chris Eckberg, Hyunsoo Kim, Daniel Campbell, Peter Zavalij, Johnpierre Paglione The RAlX (where R=Rare Earth and X=Ge, Si) family has been recently identified as a large class of Weyl semimetal based on systematic first-principles band structure calculations. Because, depending on the rare earth element, RAlX can have no local moment ordering, be ferromagnetic or antiferromagnetic, the family may offer a possibility of realization of all different types of emergent Weyl fermions, i.e. inversion-symmetry breaking and time-reversal breaking, type-I and type-II. Here, we present details of flux growth, crystal structure and physical properties of CeAlGe and CeAlSi single crystals. Both compounds show multiple magnetic transitions with the highest ferromagnetic ordering transition at 5 and 9 K, respectively, and a few metamagnetic transitions in the field-dependant magnetization. Our results are important for all members in the RAlX family. |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P21.00005: Electronic and magnetic properties of CrVTiAl room temperature spin filter films Gregory Stephen, Gianina Buda, Michelle Jamer, Christopher Lane, Staszek Kaprzyk, Bernardo Barbiellini, Arun Bansil, Laura Lewis, Donald Heiman Spin filter materials (SFMs) are magnetic semiconductors with different bandgaps for each spin direction, which provide a promising alternative to present methods of spin-current generation. When used as a tunneling barrier between nonmagnetic metallic contacts, the SFM can block one spin direction to produce a highly spin-polarized current. Traditional SFMs have low magnetic transition temperatures making them unsuitable for room temperature applications. Their large magnetic moments produce strong fringing fields that would be detrimental to nearby magnetic elements in devices. The Heusler compound CrVTiAl is a promising new SFM candidate due to its predicted high Curie temperature and near-zero magnetic moment. CrVTiAl thin films have been synthesized on various substrates by magnetron sputtering and subsequently annealed. The magnetic moment is confirmed to be small and is nearly temperature independent, consistent with the behavior of a compensated ferrimagnet. The temperature-dependent resistivity shows small-bandgap semiconducting behavior. The existence of semiconducting behavior is in accordance with our DFT calculations and could lead to the realization of a room temperature spin filter device. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P21.00006: Atomic disorder induced modification of magnetization in MnCrVAl Juliana Herran, Rishabh Dalal, Paul Gray, Parashu Kharel, Pavel Lukashev Spin-gapless semiconductors (SGS) are recently discovered materials which are characterized by a zero band gap in one spin channel and a finite band gap in the other channel. We have investigated the physical mechanisms behind experimentally observed magnetization reduction in a potential SGS compound MnCrVAl by analyzing various atomic disorder schemes. We show that depending on the degree of disorder, exchanging atomic positions between Mn/Cr and V/Al leads to reduced total magnetization due to either spin flip, or vanishing spin magnetic moments. The latter is attributed to the itinerant character of magnetism, and to the frustration of antiferromagnetic exchange interactions. Besides, we demonstrate that in certain disordered structures the spin polarization of MnCrVAl significantly increases, reaching the half-metallic state. We also show that antisite disorder does not result in significant reduction of magnetization. These findings may contribute to understanding the role of atomic disorder on magnetic properties of materials with potential applications in spin-based electronics. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P21.00007: Extreme Magnetoresistance in Magnetic Rare Earth Monopnictides Linda Ye, Takehito Suzuki, Christina Wicker, Joseph Checkelsky The acute sensitivity of the electrical resistance to magnetic fields known as extreme magnetoresistance (XMR) has recently been explored in a new materials context with topological semimetals. Exemplified by WTe2 and rare earth monopnictide LaSb, these semimetals tend to be non-magnetic and show XMR driven by intrinsic electronic structure. Here we explore transport in magnetic members of the latter family. In particular, we find that CeSb exhibits XMR in excess of 1.6×106 % at fields of 9 T and the XMR is strongly modulated by the magneto-orbital order. The magnitude of the XMR exceeds other rare earth monopnictides and follows non-saturating power law to fields above 30 T. Comparison to the orbitally quenched GdBi highlights the unique combination of orbital inversion and type-I magnetic ordering in CeSb in determining its large response. These findings suggest a paradigm for magneto-orbital control of XMR and are relevant to the understanding of rare earth-based correlated topological materials. Reference: Arxiv/1704.04226. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P21.00008: Anomalous Magnetoresistance in Antiferromagnetic Semiconductor NaMnBi Aaron Wegner, Junjie Yang, Despina Louca The robustness of antiferromagnetic order to perturbations from external magnetic fields and the lack of a net moment give antiferromagnetic (AFM) materials advantages over ferromagnetic materials for potential spintronic device applications. The development of AFM systems with interesting properties is vital to the realization of AFM spintronics. The semiconductor NaMnBi (TN ~340 K) exhibits anomalous magnetoresistance depending on growth conditions, with after growth quenching increasing the positive MR from 25% at 2 K and 9 T in the unquenched sample to 10000% after quenching, which also introduces hysteresis in the magnetic susceptibility. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P21.00009: Molecular Beam Epitaxy and Magnetotransport of InBi and InNBi Crystals for High Spin-Orbit Interaction Phillip Dang, Debdeep Jena Bismuth-containing compounds have gained traction in recent years due to the high spin-orbit coupling and bandgap bowing effects of the Bi atom. Bi is a heavy group V element in the same table as N, P, As, and Sb and has been incorporated in dilute amounts in InGaAs and InGaSb. However, there have been few reports of MBE-grown III-Bi binary or III-Nitride-Bi ternary alloys. Here we report the growth of InBi and InNBi films using molecular beam epitaxy. InBi is grown on high-resistivity Si(111) substrates at low temperatures due to the low eutectic point of the indium-bismuth system. By growing significantly thick films in a Bi-rich regime, we obtain coalesced films. Temperature-dependent Hall effect transport and resistivity measurements were performed on these films. We observe a change in the Hall-effect sign from positive to negative due to the change in majority carrier type of Bi-rich InBi and Bi films as temperature decreases. A sign change in the room temperature majority carrier type also appears with increasing indium content in InBi. We additionally discuss the methods used to incorporate Bi into InNBi films grown on GaN/SiC substrates with hopes of introducing high spin-orbit coupling into the GaN material system, where it is nearly absent due to the light N atoms. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P21.00010: Polymer microwire devices for the exploration of the non-linear magnetic resonance domain Shirin Jamali, Gajadhar Joshi, Hans Malissa, John Lupton, Christoph Boehme Electric currents in organic thin-films under bipolar charge carrier injection conditions are sensitive probes for non-linear magnetic resonance phenomena as they are controlled by the singlet−triplet ratios of recombining electron−hole pairs. By probing these current, magnetic resonance becomes detectable at very low magnetic fields where spin polarization is absent. We use this to study ultrastrong light-to-matter coupling regimes, in which charge carrier (polaron) spin Rabi frequencies are in the same magnitude range as the Zeeman frequencies of these systems. To achieve such an experiment, we have raised the AC driving field B1 of the magnetic resonant excitation above the static resonance field B0 [1]. Technologically, this is achieved by scaling of the thin films to the micrometer domain and by fabrication directly on top of RF microwires, within entirely monolithic thin-film device structures. When ultrastrong light−matter coupling is achieved, the individual resonant spin transitions of electron−hole pairs become indistinguishable and a collective triplet state formation occurs, causing a pronounced quenching of the recombination current. [1] S. Jamali, et al., Nano Lett., 17, 4648 (2017). |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P21.00011: Spin fluctuations and magneto-elastic coupling in the ferromagnetic van der Waals semiconductor CrSiTe3 Alon Ron, Eli Zoghlin, Stephen Wilson, David Hsieh The transition metal trichalcogenide CrSiTe3 is a layered van der Waals semiconductor that has recently been proposed to retain its long-range ferromagnetic order even in the atomically thin limit. Here we examine the nature of the bulk ferromagnetic phase transition using a suite of static and time-resolved optical probes including second harmonic generation, magneto-optical Kerr rotation and optical reflectivity. We show that strong magnetic fluctuations persist far above the Curie temperature, attesting to the strong two-dimensional character of ferromagnetism even in bulk crystals. We also identify strong coupling between the ferromagnetism and specific phonon modes. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P21.00012: Tuning Thermoelectric Properties of RuSb2 by Mn doping Hong Chang, William Shelton, Xin Gui, Weiwei Xie, Roshan Nepal, Lingyi Xing, Ramakanta Chapai, Rongying Jin Narrow-gap semiconductor RuSb2 is known to exhibit large thermopower, promising for thermoelectric application. However, its low electrical conductivity and high thermal conductivity lead to low figure of merit. To alter these properties, we have grown Mn-doped RuSb2 single crystals, which form an orthorhombic structure. Compared to the parent compound, 8% Mn doping results in better electrical conduction and lower thermal conductivity, while thermopower is reduced. We discuss the Mn doping effect based on both experimental results and theoretical calculations. |
Wednesday, March 7, 2018 5:18PM - 5:30PM |
P21.00013: Perfect spin filter by periodic drive of a ferromagnetic quantum barrier Sebastian Eggert, Thuberg Daniel, Enrique Munoz, Sebastian Reyes We consider the problem of particle tunneling through a periodically driven ferromagnetic quantum barrier connected to two leads. The barrier is modeled by an impurity site representing a ferromagnetic layer or quantum dot in a tight-binding Hamiltonian with a local magnetic field and an AC-driven potential, which is solved using the Floquet formalism. Our results show that the time-periodic potential causes sharp resonances of perfect transmission and reflection, which can be tuned by the frequency, the driving strength, and the magnetic field. We demonstrate that a device based on this configuration could act as a highly-tunable spin valve for spintronic applications. |
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