Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session D57: Spin Dependent Transport II |
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Sponsoring Units: GMAG Chair: Stuart Calder, Oak Ridge National Laboratory Room: Room 303 |
Monday, March 6, 2023 3:00PM - 3:12PM |
D57.00001: Emergence of asymmetric skew-scattering dominated anomalous Nernst effect in spin gapless semiconductors Co1+xFe1-xCrGa Amit Chanda, Deepika Rani, Jadupati Nag, Aftab Alam, K. G Suresh, Manh-Huong Phan, Hariharan Srikanth
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Monday, March 6, 2023 3:12PM - 3:24PM |
D57.00002: Anomalous Hall effect in Platinum/Nickel-Cobaltite bilayer. Bharat Giri Spin structure of materials plays important roles in their transport properties. In order to study whether the spin interaction at the interface between ferrimagnetic NiCo2O4 (NCO) and strongly spin-orbit coupled metal Platinum (Pt) generates novel spin structure, we prepared Pt/NCO bilayer structures on MgAl2O4 (001) substrates using pulsed laser deposition (PLD) and studied the spin transport properties at various temperature with different NCO thickness. In addition to the anomalous Hall effect expected from NCO, we observed asymmetric topological-Hall-like effects (humps). The magnitude of the humps and the magnetic field where the humps appear change dramatically with temperature, which is correlated with the coercive field of NCO. These results suggest complex spin interactions at the NCO/Pt interface which may give rise to topological spin texture. |
Monday, March 6, 2023 3:24PM - 3:36PM |
D57.00003: Impact of Boron doping to the tunneling magnetoresistance of Heusler alloy Co2FeAl Ali Habiboglu, Yash Chandak, Pravin Khanal, Bowei Zhou, Carter Eckel, Jack O'Brien, Weigang Wang Co-based Heusler alloys as Co2FeAl (CFA) have been of noteworthy interest for Magnetic Tunnel Junctions (MTJs) due to having high curie temperature, high spin polarization, and low damping coefficient. High Tunneling Magneto Resistance (TMR) values usually are obtained from epitaxial CFA MTJs deposited at high temperature on a MgO seed-layer or MgO substrate. In this work, the deposition is done at room temperature on a conventional thermally oxidized silicon wafer without a seed-layer. The epitaxial structure of ferromagnetic electrodes along with the insulating barrier is obtained by solid state epitaxy through the crystallization of MgO during post-deposition annealing, which is a critical step to form the symmetry-conserved coherent tunneling channels. Surface roughness and the crystal structure is improved and hence an enhancement of TMR is observed through the incorporation of B in the Co2FeAl electrodes. This work is supported by NSF and DARPA. |
Monday, March 6, 2023 3:36PM - 3:48PM |
D57.00004: The evolution of Berry curvature under hydrostatic pressure on compensated ferrimagnet Mn3Al Guihyun Han, Minkyu Park, Sonny H. Rhim The evolution of Berry curvature under hydrostatic pressure is studied in Mn3Al, a compensated ferrimagnetic Heusler compound. The pressure affects the occupation of certain k points, which influences the Berry curvature thereby affecting the anomalous (AHE), the spin Hall effect (SHE), and the anomalous Nernst effect (ANE). More specifically, AHE and SHE exhibit quite similar behavior due to half-metallicity, which is governed by the sum of Berry curvature of occupied bands. On the other hand, ANE reflects Berry curvature on the Fermi surface. In addition, at μ=0 eV,where nodal line exits, AHE, SHE, and ANE are compared with . |
Monday, March 6, 2023 3:48PM - 4:00PM |
D57.00005: Electrical detection of magnetization of a layered semiconducting ferromagnet using WTe2 I-Hsuan Kao, Sean Yuan, Jyoti Katoch, Simranjeet Singh Spin-orbit torque (SOT) switching devices fabricated by combining van der Waals (vdW) based semiconducting ferromagnets (FMs) and Weyl semimetal (WSMs) are appealing because of electric field-controlled magnetism and unconventional charge to spin conversion, which can be exploited for modular memory and logic devices. For instance, the vdW based FM semiconductors, such as Cr2Ge2Te6 (CGT), offer us the opportunity to study SOT devices where electric field-controlled magnetism can be used for enhanced device functionalities1. Also, we have recently shown that field-free deterministic switching of perpendicular magnet can be obtained by utilizing the unconventional spin orbit torque in WTe22. In SOT devices, the electrical readout of the semiconducting FM layer is essential for device functionality. Electrical detection of magnetization in conventional insulating/ semiconducting ferromagnet (FM) is routinely achieved by utilizing spin hall effect generated by the adjacent heavy metal layer3. The electrical readout of magnetization in 2D semiconducting FM has been demonstrated by coupling Cr2Ge2Te6 with heavy metals4 and topological insulators5. However, few reports have shown electrical detection in a vdW based semimetal/FM-semiconductor heterostructures. Our initial results have demonstrated observation of spin Hall-induced anomalous Hall resistance and spin magnetoresistance in WTe2/CGT bilayers. On the same device, the resistance of individual CGT is more than 100 times higher than the resistance of the bilayer structure, therefore most of the current is flowing through WTe2 layer. We will present detailed measurements, which are required to understand the the interplay between the electric gating and observed spin magnetoresistance at the interface in WTe2/CGT bilayer systems. |
Monday, March 6, 2023 4:00PM - 4:12PM |
D57.00006: Tuning the oxygen ratio in perpendicular magnetic tunnel junctions with MgAl2O4 barriers Pravin Khanal, Bowei Zhou, Magda Andrade, Christopher Mastrangelo, Ali Habiboglu, Arthur Enriquez, Daulton Fox, Kennedy Warrilow, Wei-Gang Wang MgO is the barrier of choice for modern magnetic tunnel junctions (MTJs). However, the lattice parameter of MgO cannot be tuned to match with other ferromagnetic materials which limits the practical application of MTJ devices. Therefore, the exploration of other barriers with the tunable lattice parameter is important to design the energy efficient MTJs. Here we present our study on perpendicular MTJs with MgAl2O4 barrier. A unique three steps deposition process has been employed to enhance the O2 concentration in the barrier, without over-oxidizing the bottom CoFeB electrode. As a result, the TMR ratio greater than 60 % is achieved for the first time in perpendicular MTJs with MgAl2O4-barrier. An interfacial perpendicular magnetic anisotropy energy density of 2.25 mJ/m2 is obtained for the samples annealed at 400°C. The Vhalf, bias voltage at which the tunneling magnetoresistance drops to half of the zero-bias value, is found to be about 1V, which is substantially higher than that of MgO-based junctions. |
Monday, March 6, 2023 4:12PM - 4:24PM |
D57.00007: Angular Dependent Magnetoresistance Measurments in Manganese Telluride Thin Films Joseph A Lanier, Jose Flores, Menglin Zhu, Jinwoo Hwang, Fengyuan Yang Antiferromagnets (AFM) have drawn interests for use in spintronic devices due to their fast dynamics and stability against external fields. Manganese telluride (MnTe) exhibits a Néel Temperature of 307 K and shows a similar magnetic structure to the well-studied α-Fe2O3. In this work we report angular dependent spin-hall magnetoresistance (SMR) measurements of α-MnTe/Pt bilayers. X-ray diffraction scans show high crystalline quality for α-MnTe films of thicknesses from 15 to 60nm on InP(111) substrates. Atomic Force Microscopy reveals the appearance of triangular plateaus in MnTe epitaxial films which suggests good in-plane lattice matching. SQUID magnetometry shows the emergence of a net moment in these antiferromagnetic films, which may influence the SMR in these bilayers. We observe unexpected behavior in angular dependent magnetoresistance signals for all thicknesses of MnTe films. A positive SMR signal is a characteristic of ferromagnets and differs from the negative SMR signal found in α-Fe2O3/Pt bilayers. We explain the unexpected characteristics in the SMR signal and the potential mechanisms underlying this behavior. |
Monday, March 6, 2023 4:24PM - 4:36PM |
D57.00008: Nernst measurements in thin Pt and W wires at low temperatures Tanner Legvold, Shusen Liao, Renjie Luo, Douglas Natelson With the rapid growth of interest in spin caloritronics studies of magnetic insulators, including at cryogenic temperatures, it is important to understand potential confounding effects that arise in strong spin-orbit metals. We provide detailed measurements of the Nernst response of Pt and W wires at low temperatures utilizing an experimental configuration familiar from local spin Seebeck measurements. For thin wires of Pt on oxidized Si substrates, we find that the Nernst response at fixed power decreases with increasing temperature. We use finite element thermal modeling and Johnson-Nyquist noise measurements of the wires to evaluate the thermal environment during the Nernst measurements. We compare the measured results with theoretical expectations for these systems. |
Monday, March 6, 2023 4:36PM - 4:48PM |
D57.00009: Strain induced spin-gapless semiconductivity in FeCrTiAl Pavel Lukashev, Gavin M Baker, Jax G Wysong, Paul M Shand, Parashu R Kharel Spin-gapless semiconductors (SGS) represent a new class of materials with potential applications in spin-based electronics. Here, we performed a combined theoretical and experimental study of FeCrTiAl, a quaternary Heuser compound that was recently predicted to exhibit nearly SGS properties. Our calculations indicate that this material undergoes a transition from quasi-SGS to SGS under mechanical expansion (approximately, 4% increase of the lattice constant). At the same time, mechanical compression results in reduced spin-polarization of FeCrTiAl. Potentially, a negative pressure (mechanical expansion) may be achieved either by applying an epitaxial strain in thin-film geometry, or by chemical substitution, e.g. with non-magnetic element of larger atomic radius. Interestingly, further increase of the lattice parameter (~6%) leads to a type-2 to type-1 SGS transition. However, such large values of mechanical strain may be difficult to achieve in practice. Our results may provide guidance for further research on strain induced manipulation of electronic properties of spin-gapless semiconductors. |
Monday, March 6, 2023 4:48PM - 5:00PM |
D57.00010: Plasma-Treated Bottom Electrode-Based Molecular Spintronic Device Fabrication for Extremely High Switching Marzieh Savadkoohi, Eva Mutunga, Andoniaina M Randriambololona, Hayden Brown, Pius Suh, Pawan Tyagi Tunneling magnetoresistance (TMR) is a quantum mechanical phenomenon and an important effect that happens in magnetic tunnel junctions (MTJ). TMR reaches its maximum value when electrodes’ spins take parallel orientations with respect to each other. Along with bias voltage, barrier type and thickness, and structural asymmetry in MTJs, electrodes’ quality play an important role in gaining high TMR in molecular spintronic devices. A defect-free tunnel barrier reduces the charge transport competing effect by the insulator and enhances the transport via conducting molecular channels. This work investigates the fabrication defects of MTJ tunnel barriers caused by the bottom electrode and uses various strategies to minimize and remove those defects through different techniques. We used the Taguchi Design of Experiment, Oxygen plasma cleaning, and Argon Etching to minimize interlayer coupling between ferromagnetic electrodes. Our results showed a significant difference in bottom electrode edge geometry and surface roughness upon post-lift-off Ar Etch compared to other techniques. We observed an extremely high switching ratio (~1000 times increase in TMR) upon removal of pinhole-type defects and hillocks in our SMM-based molecular spintronic device. IV measurements, MFM, and KPFM scans support the improvements of the device characteristics after fabrication optimization. |
Monday, March 6, 2023 5:00PM - 5:12PM |
D57.00011: Thickness dependent Magnetoresistance (MR) in Europium (Eu) metal Thin Films Narendra Shrestha, Jinke Tang We have prepared Eu metal thin films of different thickness under a similar condition via Pulsed Laser Deposition (PLD) technique and studied the transport properties by four-probe method using Physical Property Measurement System (PPMS). In addition to showing negative MR at high temperature and positive MR at low temperatures, thicker films exhibit hysteretic oscillation above 30 K which is believed to be associated with the re-distribution of the antiferromagnetic domains in Eu. |
Monday, March 6, 2023 5:12PM - 5:24PM |
D57.00012: Impact of Interactions on Topological Magnonic Transport Konstantinos Sourounis, Aurélien Manchon The topological transport of magnons is a popular alternative to the electronic transport for novel spintronic applications due to the absence of Joule heating and the large range of frequencies in these systems. The magnonic transport has been investigated in various platforms (ferro- and antiferromagnets) and is characterized by anomalous mechanisms such as the thermal Hall effect and the magnon Nernst effect. The usually employed framework of Linear Spin Wave Theory, in fact, does not take into account effects as magnon |
Monday, March 6, 2023 5:24PM - 5:36PM |
D57.00013: Enhanced Room-Temperature Spin Hall Magnetoresistance in Single-Domain BiFeO3 and Pt Bilayer Yongjian Tang, Pratap Pal, Neil G Campbell, Jonathon L Schad, Tianxiang Nan, Mark S Rzchowski, Chang-Beom Eom, Daniel C Ralph Spin Hall magnetoresistance (SMR) is an effect arising at the interface between a heavy metal and a magnetic insulator. Here, we report the magnetic-field and temperature dependence of longitudinal SMR in BiFeO3/Pt bilayer samples. Multiferroic BiFeO3 epitaxial thin films are grown on STO (001) substrates with a 4° miscut toward [110], resulting in a single ferroelectric/ferroelastic domain, which is verified by piezoresponse force microscopy (PFM) and reciprocal space mapping (RSM). The first-harmonic SMR in the BiFeO3/Pt samples shows a typical cos[2(φ-φ0)] dependence, where φ is the angle between the current and the external magnetic field, with a SMR amplitude that increases quadratically with field magnitude as expected for an antiferromagnet/metal sample. However, unlike the usual SMR in ferromagnet/metal or antiferromagnet/metal samples, BiFeO3/Pt has the maximum SMR signal at an angle different than φ0 = 0° or 90°. We believe that this might be due to the more complicated spin structure associated with the spin cycloid, which can be further probed from various other techniques such as neutron diffraction and non-resonant x-ray magnetic scattering (NXMS). |
Monday, March 6, 2023 5:36PM - 5:48PM |
D57.00014: Perpendicular magnetic anisotropy, tunneling magnetoresistance and spin-transfer torque effect in magnetic tunnel junctions with Nb layers Bowei Zhou, Pravin Khanal, Onri J Benally, Deyuan Lyu, Daniel B Gopman, Arthur Enriquez, Ali Habiboglu, Kennedy Warrilow, Jian-Ping Wang, Weigang Wang Nb and its compounds are widely used in quantum computing due to their high superconducting transition temperatures and high critical fields. Devices that combine superconducting performance and spintronic non-volatility could deliver unique functionality. Here we report the study of magnetic tunnel junctions with Nb as the heavy metal layers. An interfacial perpendicular magnetic anisotropy energy density of 1.85 mJ/m2 was obtained in Nb/CoFeB/MgO heterostructures. The tunneling magnetoresistance was evaluated in junctions with different thickness combinations and different annealing conditions. An optimized magnetoresistance of 120% was obtained at room temperature, with a damping parameter of 0.011 determined by ferromagnetic resonance. In addition, spin-transfer torque switching has also been successfully observed in these junctions with a quasistatic switching current density of 0.73 MA/cm2. |
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