Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V37: Oxide Thin Films for Spintronics and MagnonicsFocus Live
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Sponsoring Units: GMAG DMP DCOMP Chair: Purnima Balakrishnan, Natl Inst of Standards&Tech; Ryan Need, University of Florida |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V37.00001: Perpendicular magnetic anisotropy and low magnetic damping in epitaxial Li0.5Al1.0Fe1.5O4 thin films Xin Yu Zheng, Sanyum Channa, Zbigniew Galazka, Yuri Suzuki Magnetic materials with perpendicular magnetic anisotropy (PMA) and low magnetic damping provide promising model systems for high information density storage applications. However, the pool of materials with both PMA and low damping is extremely limited. In this talk, we present our preliminary results on simultaneously achieving PMA and low damping in spinel oxide Li0.5Al1.0Fe1.5O4 (LAFO) films grown on (001) oriented MgGa2O4. SQUID measurements show strong PMA with a low coercivity of 2 mT in the out-of-plane (OOP) configuration, and broadband OOP ferromagnetic resonance (FMR) measurements show a Gilbert damping parameter on the order of 0.001. This damping value rivals those found in yttrium iron garnet films and is the lowest reported to date for a non-garnet structure material with PMA. The relatively simple crystal structure of the spinel compared to the garnets also allows for coherent interfacing with other oxides, diversifying its applications. Our work shows that LAFO is a promising new material in the field of spintronics for high density information storage applications. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V37.00002: Spin-current generation and Spin-Orbit Torque switching in Perpendicularly Magnetized Insulating Ni0.65Zn0.35Fe1.2Al0.8O4 films Sanyum Channa, Zbigniew Galazka, Satoru Emori, Matthew T Gray, Yuri Suzuki Perpendicular magnetic anisotropy (PMA) and low magnetic damping are key features in developing next-generation spin-torque based technologies. In this talk, we demonstrate PMA as well as low damping in spinel ferrite Ni0.65Zn0.35Fe1.2Al0.8O4 (NZAFO) films grown on (001)-oriented MgGa2O4 (MGO) substrates under tensile strain. Structural characterization indicates epitaxial growth of NZAFO on MGO with excellent crystallinity and mosaic spread Δω ~ 0.06°. Bulk SQUID magnetometry indicates an out-of-plane magnetic easy axis with a coercivity as low as 2 mT in films of thickness ~10-20 nm. Ferromagnetic resonance with an out-of-plane field reveals narrow linewidths on the order of 1 mT and Gilbert damping parameters of α ≈ 5-9×10-4, significantly lower than previous studies. These damping values are some of the lowest reported to date for a ferromagnetic insulator with PMA. We will incorporate NZAFO with Pt in bilayers to study spin pumping and spin-orbit torque switching. NZAFO can be coherently interfaced with other spinels as well as other oxides, and therefore holds great promise for future spin current-based applications. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V37.00003: Magnon transport in three-terminal YIG/Pt nanostructures studied by dc and ac detection techniques Janine Gückelhorn, Tobias Wimmer, Stephan Geprägs, Hans Huebl, Rudolf Gross, Matthias Althammer Magnon-mediated spin currents provide novel routes for spin transport and spin-based information processing. In our experiments, we deposit three electrically isolated platinum (Pt) strips on top of an yttrium iron garnet (YIG) thin film. The outer Pt strips act as spin current injector (source) and detector (drain). The center strip (gate) is utilized to modulate the magnon transport via an applied charge current. In the injector and modulator the charge current flow controls the magnon density in YIG via both the spin Hall effect and Joule heating. We compare two measurement schemes, a dc-technique utilizing the current reversal method and an ac-technique based on lock-in detection. We demonstrate that both techniques are well suited to investigate incoherent magnon transport in these three-terminal devices. However, while at low modulator charge current both schemes yield quantitatively identical results, we find clear differences above a certain threshold current. This allows us to get access to higher order terms originating from the injector current [1]. |
Thursday, March 18, 2021 3:36PM - 4:12PM Live |
V37.00004: Coherent ac spin current transmission across an antiferromagnetic CoO insulator Invited Speaker: Qian Li The recent discovery of spin current transmission through antiferromagnetic insulating materials opens up vast opportunities for fundamental physics and spintronics applications. The question currently surrounding this topic is: whether and how could THz antiferromagnetic magnons mediate a GHz spin current? This mismatch of frequencies becomes particularly critical for the case of coherent ac spin current, raising the fundamental question of whether a GHz ac spin current can ever keep its coherence inside an antiferromagnetic insulator and so drive the spin precession of another ferromagnet layer coherently? Utilizing element- and time-resolved x-ray pump-probe measurements on Py/Ag/CoO/Ag/ Fe75Co25/MgO(001) heterostructures, here we demonstrate that a coherent GHz ac spin current pumped by the Py ferromagnetic resonance can transmit coherently across an antiferromagnetic CoO insulating layer to drive a coherent spin precession of the Fe75Co25 layer. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V37.00005: Observation of Antiferromagnetic Magnon Pseudospin Dynamics and the Hanle effect Tobias Wimmer, Akashdeep Kamra, Janine Gückelhorn, Matthias Opel, Stephan Geprägs, Rudolf Gross, Hans Huebl, Matthias Althammer The quantized spin excitations of an antiferromagnet can be described as pairs of spin-up and -down magnons and characterized by a magnonic pseudospin. Here, we report experiments demonstrating control of magnon spin transport and pseudospin dynamics in a 15 nm thin film of the antiferromagnetic insulator hematite (α-Fe2O3) utilizing two Pt strips for all-electrical magnon injection and detection [1]. We observe an oscillation in polarity of the magnon spin signal at the detector as a function of the externally applied magnetic field. We quantitatively explain our experiments in terms of diffusive magnon transport. In particular, we observe a coherent precession of the magnon pseudospin caused by the easy-plane anisotropy and the Dzyaloshinskii-Moriya interaction. This observation can be viewed as the magnonic analogue of the electronic Hanle effect and the Datta-Das transistor, unlocking the high potential of antiferromagnetic magnonics towards the realization of electronics-inspired phenomena. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V37.00006: Novel spin-orbit torque generation at room temperature in an all-oxide epitaxial La0.7Sr0.3MnO3/SrIrO3 system Xiaoxi Huang, Shehrin Sayed, Joseph Mittelstaedt, Sandhya Susarla, Saba Karimeddiny, Lucas Caretta, Hongrui Zhang, Tanay Gosavi, Farzad Mahfouzi, Qilong Sun, Peter Ercius, Nicholas Kioussis, Sayeef Salahuddin, Daniel C Ralph, Ramamoorthy Ramesh An all-oxide, SrTiO3 (STO)// La0.7Sr0.3MnO3 (LSMO)/ SrIrO3 (SIO) heterostructure with lattice-matched crystal structure has been synthesized, exhibiting an epitaxial and atomically-sharp interface between the ferromagnetic LSMO and the high spin-orbit-coupled metal SIO. We use spin-torque ferromagnetic resonance to probe the effective magnetization and the SOT efficiency in LSMO/SIO heterostructures grown on STO substrates. Remarkably, epitaxial LSMO/SIO exhibits a large SOT efficiency, = 1, while retaining a reasonably low shunting factor and enhances the effective magnetization of LSMO by 50 percent. Our findings highlight the significance of epitaxy as a powerful tool to achieve a high SOT efficiency, explore the rich physics at the epitaxial interface, and open up a new pathway for designing next-generation energy-efficient spintronic devices. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V37.00007: Optical Measurements of Epitaxially Grown Ferrimagnetic Insulator Thin Films Timothy Nunley, Liang Juan Chang, Side Guo, David Lujan, Shang-Fan Lee, Fengyuan Yang, Xiaoqin (Elaine) Li Ferrimagnetic insulators exhibit attractive properties for low-loss spintronic applications. Recently, multiple groups have reported the detection of chiral magnetism and the topological Hall effect in Pt/Tm3Fe5O12 (TmIG) bilayers, suggesting a promising perspective for hosting small skyrmions. We investigate Tm3Fe5O12 thin films with atomically sharp interfaces and properties tunable via eptaxial strain. Sensitive magneto-optical Kerr effect measurements allow us to compare a series of samples with TmIG thickness in the range of 1.9 to 10 nm. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V37.00008: Spin Hall magnetoresistance in Pt/hexagonal rare-earth ferrite heterostructures Jing Li, Yu Yun, Xiaoshan Xu Multiferroic materials are promising for spintronic application due to their strongly coupled ferroic orders. Hexagonal rare-earth ferrites (h-RFeO3) possess ferroelectric and anti-ferromagnetic orders that could modify spin-charge conversion with a large electric polarization. We report measurements of field-dependent and angle-dependent magnetoresistance from Pt/h-RFeO3 heterostructures at various temperatures. It is found that spin Hall magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) coexist in the bilayers. SMR has a temperature dependence similar with those from Pt/ferromagnetic insulators, but the temperature dependence of AMR reaches local maximum around Neel temperature of h-RFeO3 and changes sign at lower temperatures. The results are discussed within the frame of SMR theory by considering the magnetocrystalline anisotropy of h-RFeO3. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V37.00009: Towards skyrmionic spin textures combined with SrTiO3 two-dimensional electron gases Luis Moreno, Srijani Mallik, Karim Bouzehouane, Sergio Valencia, Nicolas Reyren, Agnès Barthélémy, Manuel Bibes SrTiO3 (STO) two-dimensional electron gases (2DEGs) can be formed by depositing reactive metals such as Al onto STO single crystals: the metal oxidizes, forming oxygen vacancies in the STO and thus doping it in electrons. Such 2DEGs can then be used to interconvert spin and charge currents with great efficiency. In this presentation we will show that the metal oxide (e.g. AlOx) thus formed can be combined with ferromagnetic and heavy-metal-based ultrathin films to generate various types of magnetization configurations with in-plane or out-of-plane anisotropy, depending on their relative thicknesses. For specific compositions, these multilayers harbor magnetic bubbles, as imaged by magnetic force microscopy and X-ray photoemission electron microscopy, that likely have a skyrmionic character, due to the expected Dzyaloshinskii-Moriya interaction caused by the strong broken inversion symmetry. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V37.00010: Zero-bias Giant Rashba Spin-Orbit Coupling Controlled by Carrier Modulation Layer Ganesh Ji Omar, Ariando Ariando The Landauer’s principle dictates a fundamental physical limitation for the switching energy. A primary solution in breaking this limitation is to utilize the spin-orbit coupling (SOC) effect at broken inversion symmetry, as it allows easy manipulation of spin currents. However, this SOC effect is often quite weak, especially in the absence of external voltage biases. We report a four-fold SOC enhancement at zero bias voltage and pronounced SOC evolution in correlated LaAlO3-SrTiO3 heterostructures buffered by a carrier modulating LaFeO3 layer. We use an entirely new model to provide evidence of generating Rashba SOC. Correlating the magnetotransport data with first-principles calculations and high-resolution electron microscopy, we reveal that its origin lies in the asymmetric hybridization of the interfacial wavefunctions. Our results open hitherto unexplored avenues of generating and controlling Rashba coupling to design next-generation two-dimensional electron system based spin-orbitronic devices. |
Thursday, March 18, 2021 5:24PM - 5:36PM Not Participating |
V37.00011: Magnetic properties of Manganite/Iridate bilayers. Suzanne G.E. te Velthuis, Stephan Rosenkranz, Xiao Wang, Javier Tornos, Fernando Gallego, David J Keavney, John Freeland, Yongseong Choi, Joerg Strempfer, Daniel Haskel, Brian James Kirby, Timothy R Charlton, Jacobo Santamaria The relationship between spin-orbit coupling (SOC), emergent topological states, and spin Hall effects, which are highly relevant for spintronics, has driven the interest in materials with strong SOC in recent years. To probe the influence of SOC at 3d-5d complex oxide interfaces, we have investigated ferromagnetic La0.7Sr0.3MnO3/SrIrO3 bilayers deposited on SrTiO3. We find that depending on the growth order, the coercive field of the magnetization loop differs significantly at low temperatures. Similar to previous reports, a net moment on Ir has been recorded with element specific XMCD experiments, which is aligned antiparallel to the Mn moments within the manganite. We find that the Ir moment does not follow the same temperature dependence as the magnetization of the manganite, and is limited to the interface. Possible origins of this result will be discussed. |
Thursday, March 18, 2021 5:36PM - 5:48PM On Demand |
V37.00012: High-quality single-crystalline Europium iron garnet films with perpendicular magnetic anisotropy by sputtering Meng-Xin Guo, Y.C. Liu, Chi-Nan Wu, C. K. Cheng, W. N. Chen, Tian-Yue Chen, S.Q. Zhou, Chi-Feng Pai, Shang-Fan Lee, Minghwei Hong, Jueinai Kwo We demonstrate the high-quality europium iron garnet (EuIG) thin films with strain-induced perpendicular magnetic anisotropy (PMA) grown on GGG (001) using an off-axis sputtering technique. Our thin film samples exhibit an extremely smooth, particle-free surface with root-mean-square roughness as low as 0.1 nm. High-resolution synchrotron radiation x-ray diffraction analysis revealed excellent crystallinity of the films and the reciprocal lattice mapping (RSM) showed the film is lattice matched to the substrate without strain relaxation. By adjusting the Eu/Fe composition ratio, we are able to fine-tune the magnetic properties such as saturation magnetization (MS), coercive field (HC), and strength of PMA field (H⊥). The relative orientations of the magnetic moments of the cations were probed by x-ray magnetic circular dichroism (XMCD) measurement at Eu M4, 5 and Fe L3, 4 absorption edges. Finally, we demonstrate the current-induced magnetization switching in Pt/EuIG structure with a low critical switching current density of 3.5×106 A/cm2, showing great potential for low-dissipation spintronic devices. |
Thursday, March 18, 2021 5:48PM - 6:00PM On Demand |
V37.00013: SrTiO3-based 2-dimensional electron gases for ultralow power spintronics Manuel Bibes SrTiO3 (STO) 2DEG may be exploited to interconvert spin and charge currents with high efficiencies. By applying a gate voltage, we tune the position of the Fermi level in the complex multi-orbital structure of STO, which results in a strong variation of the conversion amplitude. This can be related to the band structure through ARPES experiment and tight-binding calculations. I will present results from both spin-charge conversion where spins are injected by spin pumping in a FMR cavity and detected as a transverse voltage1, and from charge-spin conversion probed through the bilinear magnetoresistance (BMR) effect. Through a semi-classical model, the analysis of the BMR amplitude yields a measure of the Rashba coefficient2. In a second part, I will present gate-controlled, all-electrical spin current generation and detection in planar nanodevices free from ferromagnets3. Finally, I will propose a new approach to achieve a non-volatile control of spin-charge interconversion with Rashba 2DEGs based on ferroelectricity rather than ferromagnetism, that may pave the way to an entirely new family of ultralow power spintronics devices4. |
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