Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B53: Thin Films: Spintronics/Spin-Orbit/Hall EffectsFocus Recordings Available
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Sponsoring Units: GMAG Chair: Jason Hoffman, Harvard Room: McCormick Place W-475B |
Monday, March 14, 2022 11:30AM - 12:06PM |
B53.00001: Exotic Magnetic Properties In Strain-Modulated Slater-Mott Crossover Regime Invited Speaker: Junyi Yang Novel states and emergent phenomena arising from the interplay of charge, spin, and structural degree of freedoms in complex oxides are of particular interest in both fundamental physics and engineering application. Recent developments in 5d transition metal oxides, which have a strong spin-orbital coupling and an intermediate electronic correlation, have unraveled various exotic phenomena that are rarely observed or absent in 3d transition metal oxides. One of the prominent examples is the pseudospin-½ square lattice in iridates that can simulate the 2D single-orbital Hubbard Hamiltonian with a hidden SU(2) symmetry in the Slater-Mott crossover regime, in contrast to the strong antiferromagnetic (AFM) Mott insulating state in 3d transition metal oxides. By creating artificial superlattice of the pseudospin-½ square lattice, we are able to capture the anomalous transport behavior in this crossover regime. We have also achieved modulating the correlation strength of the pseudospin-1/2 electronic state across this regime by applying epitaxial strain and directly probing the AFM order parameter in these ultrathin samples. Moreover, combined dimensionality-control and site dilution over the superlattice, we have observed emergent isotropic spin fluctuations despite the planar anisotropy of the square lattice. This enhanced fluctuation enables giant responses of the AFM order to the external magnetic field. Our work has shown that pseudospin-1/2 iridate superlattice is a powerful platform to study correlation physics as well as realize function controls. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B53.00002: Competing interactions and emerging phases in low-spin d5 perovskites: Bulk and Ultrathin Films Amit Chauhan, B. R. K. Nanda Due to the delicate interplay between onsite Coulomb repulsion (U) and spin-orbit coupling (SOC), the 4d and 5d transition metal oxides have emerged out as exotic quantum materials. By performing SOC tunable DFT+U calculations supplemented with a multi-orbital Hubbard model, on bulk and thin films of the prototype system SrIrO3, we present eight electronic and magnetic phases in the U-SOC space that can be observed in the family of low-spin bulk d5 perovskites. With reduced dimensionality, we observe six unique phases. Specifically, the film terminated by IrO2 layers exhibits multiple Dirac states in the weak correlation regime. The films exhibits large magnetic anisotropy energy to become promising candidates for magnetic memory and storage devices. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B53.00003: Giant Room Temperature Spin Hall Effect in BaPb1-xBixO3 Thin Film Heterostructures Anthony L Edgeton, Michael V Patton, Neil G Campbell, Yahong Chai, Daniel C Ralph, Mark S Rzchowski, Tianxiang Nan, Chang-Beom Eom BaPb1-xBixO3 (BPBO) is a superconductor with strong spin-orbit coupling and a Tc of 11K at optimal doping ( x=0.25 ) [1], bounded by metallic BaPbO3 (x=0) and charge density wave insulator BaBiO3 (x=1) in its phase diagram. We study room temperature charge to spin conversion in BPBO/Permalloy thin film heterostructures by spin-torque ferromagnetic resonance, finding a large spin Hall angle in BPBO (x=0.25). The much smaller spin Hall angle we observe in the parent BaPbO3 (x=0) indicates a significant role of Bi in engineering the spintronic properties of this system. This work highlights the potential of BPBO and other phase-competition superconductors for superconducting spintronics. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B53.00004: Non-Linear Magnetoelectric effects in Hexagonal and Spinel Ferrite Films Gopalan Srinivasan, Maksym Popov, Igor Zavislyak This report is on electric field induced nonlinear magnetoelectric effects (NLME) in single crystals films of spinel and hexagonal ferrites. The effect manifests as variations in the magnetic order parameters that are proportional to square of the electric field [1,2]. Measurements were carried out on NiZn spinel ferrite, barium and strontium M-type hexaferrites, and Y-type hexagonal ferrite and for electric fields applied either in plane or perpendicular to the film plane. Ferromagnetic resonance (FMR) in the single domain and multidomain states at 10-58 GHz was utilized to investigate the phenomenon. The shift in the FMR resonance frequency was measured as a function of input electric power and the data were utilized to estimate the NLME induced changes in the magnetization and anisotropy field. The shift in FMR frequency and variations in the magnetic parameters were higher in the single domain state than in the multidomain state. The NLME coefficients estimated from changes in the magnetic parameters were higher for in plane E than for out of plane electric fields. A phenomenological model for the NLME effect is proposed and qualitatively accounts for the observed dependence of magnetic parameters on input power. The NLME effects in the ferrites are of importance for electrically tunable ferrite microwave signal processing devices. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B53.00005: Anomalous Hall Effect and Perpendicular Magnetic Anisotropy in Ultrathin NiCo2O4 Films Qiuchen Wu, Xuegang Chen, Xia Hong The high Curie temperature (TC) and high spin polarization of ferrimagnetic spinel NiCo2O4 (NCO) make it a promising material candidate for spintronic applications.1 We report the magnetotransport study of 1.5 uc (unit cell) to 5 uc (1.2-4 nm) epitaxial NCO thin films deposited on (001) MgAl2O4 substrates. The 3 uc and thicker NCO films exhibit metallic conduction, while the 1.5 and 2 uc films become totally insulating. Samples of all thicknesses exhibit anomalous Hall effect (AHE) below TC, with the AHE switching hysteresis revealing strong perpendicular magnetic anisotropy. For all films, the coercive field HC increases exponentially with decreasing temperature, which can be attributed to thermally activated domain wall depinning. The AHE resistance shows a nonmonotonic temperature dependence and reverses sign at low temperature. The scaling between the AHE conductivity σxy and longitudinal conductivity σxx points to the dominating dirty metal behavior. We also discuss the topological Hall effect and magnetic force microscopy studies of the ultrathin NCO films. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B53.00006: Ferroelectric field effect in ultrathin Sr2IrO4 films YUANYUAN ZHANG, Le Zhang, Xia Hong Sr2IrO4 (SIO) is a Jeff = 1/2 Mott insulator with large spin-orbit coupling and strong correlation effect. The correlated behavior depends sensitively on the charge density. In this study, we investigate the effect of ferroelectric field effect doping in ultrathin SIO films. We deposit epitaxial PbZr0.2Ti0.8O3 (PZT)/SIO heterostructures on LaAlO3 (001) substrates via off-axis RF magnetron sputtering, with atomically smooth surface and high crystallinity achieved. By switching the polarization of PZT, we demonstrate nonvolatile resistance switching in 2-3 nm SIO channels. The field effect modulation increases with decreasing channel thickness and temperature. In PZT/2.6 nm SIO, the resistance switching ratio between the polarization up and down states of PZT is ~5% at room temperature, which increases to ~10% at 10 K. We compare the results with the field effect obtained on SrIrO3 channels with similar thickness and discuss the critical material parameters that control the magnitude of the modulation. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B53.00007: Control of non-local magnon spin transport via magnon drift currents Richard Schlitz, Saul Vélez, Akashdeep Kamra, Charles-Henri Lambert, Michaela Lammel, Sebastian T Goennenwein, Pietro Gambardella A key research focus in the field of magnonics are electrically generated and detected magnon spin currents in heterostructures consisting of a magnetic insulator and a heavy metal. Careful device design enables the investigation of spin transport via magnon diffusion [1]. However, the absence of the magnon equivalent of an electric force is an obstacle for realizing the full potential of pure spin currents. In this work, we report the controlled generation of magnon drift currents in heterostructures of yttrium iron garnet and platinum. Relying on the electrical injection and detection of incoherent magnons, we find magnon drift currents that stem from the odd contribution of the interfacial Dzyaloshinskii-Moriya interaction to the magnon dispersion. By changing the orientation of the magnetic field, we can control the magnon drift, where a maximum change of the magnon propagation length by up to ±6% relative to diffusion can be achieved. We find good agreement between experiments and an extended spin transport theory which includes a finite drift velocity resulting from any inversion asymmetric interaction [2]. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B53.00008: Interfacial manipulation of spin-orbit torques in BaPb1-xBixO3/La1-xSrxMnO3 system Isaac A Harris, Lucas M Caretta, Ramamoorthy Ramesh The spin Hall effect (SHE) in a correlated electronic system can be used to apply a torque on the magnetization of an adjacent magnet, offering a promising candidate for energy efficient, nonvolatile data storage. Modifying the properties of the spin-current generating layer has provided tools with which the SHE can be controlled; however, few have studied how the interface between the magnet and the spin-current generating layer can be engineered to control the strength of a spin-orbit torque (SOT) onto the magnetization. Here, we synthesized BaPb1-xBixO3/La1-xSrxMnO3 (BPBO/LSMO) heterostructures on SrTiO3 substrates using pulsed laser deposition (PLD) to investigate how interfacial engineering can modify the strength of SOTs across the interface of the heterostructure. We modify the interface quality by manipulating PLD growth parameters and characterize the interface quality using transmission electron microscopy. We quantify the SOT strength and symmetry using spin-torque ferromagnetic resonance, illuminating the role of the interface in the strength of SOTs. With a better understanding of the role of the interface in utilizing the SHE, we will be better equipped to select for material systems that will excel in applications such as magnetic memory. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B53.00009: Spin transport in ferrimagnetic LaCrO3/LaMnO3 superlattices Xuanyi Zhang, Zhengjie Huang, Athby H Al-Tawhid, Eric Vetter, Dali Sun, Divine P Kumah Understanding the fundamental mechanisms which govern and enhance spin transport in materials is technological and scientific interest due to potential applications in novel spintronic devices and quantum computation. While spin transport in normal metals has been explored extensively, open questions remain related to the spin transport properties of antiferromagnetic and ferrimagnetic systems. Here, we studied the temperature-dependent spin coherence length in ferrimagnetic LaCrO3/LaMnO3(LCO/LMO) superlattices. The antiferromagnetic Mn-Cr coupling in LCO/LMO superlattices confirmed by X-ray circular dichroism measurements leads to a paramagnetic to ferrimagnetic transition at 100 K. Changes to the spin coherence length in the paramagnetic (above TC) and ferrimagnetic (below TC) phases are investigated by ferromagnetic resonance (FMR) spin pumping measurements. Here, ferromagnetic LaSrMnO3 or nickel alloy layers serve as the spin source/sink and are deposited adjacent to the epitaxially grown LCO/LMO superlattices. The spin coherence length of LCO/LMO system are derived from the frequency-dependence of the FMR response above and below the magnetic phase transition. By tuning the period and thickness of the LCO/LMO superlattices with atomic-scale control using the molecular beam epitaxy, we demonstrate effective pathways for modulating spin transport in artificially layered systems. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B53.00010: Anomalous Magnetoresistance by Breaking Ice Rule in Bi2Ir2O7/ Dy2Ti2O7 Heterostructure Chengkun Xing, Han Zhang, Kyle Robert Noordhoek Pyrochlore Dy2Ti2O7 is one of the most well-known spin ice prototypes that has attracted much attention due to its extensively degenerate ground state, emergent monopole excitations and coulomb phase. The ice rule can be broken when raising the temperature or applying a magnetic field along a [1,1,1] direction. The latter is known to drive the spin ice state into a 3-in-1-out state evidenced by a quantized magnetization increment. In this talk, we will discuss our recent work on synthesizing epitaxial pyrochlore heterostructures Bi2Ir2O7/Dy2Ti2O7. Bi2Ir2O7 is a paramagnetic correlated metal of the pyrochlore iridate series and in proximity to a quantum critical point of an all-in-all-out state. Systematic transport measurements show that the correlated charge carriers in Bi2Ir2O7 are highly sensitive to spin fluctuations due to breaking of the ice rule in Dy2Ti2O7, resulting in anomalous magnetoresistance. Our work demonstrates the possibility of “metallizing” insulating quantum magnets through epitaxial interfaces. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B53.00011: Enhanced ferromagnetism in (111)-oriented CaRuO3/CaMnO3 superlattices Margaret Kane, Megan Holtz, Churna B Bhandari, Purnima P Balakrishnan, Alexander Grutter, Durga Paudyal, Sashi S Satpathy, Yuri Suzuki Emergent ferromagnetism observed at (001) CaRuO3/CaMnO3 (CRO/CMO) interfaces is attributed to charge transfer from the itinerant metal CRO into antiferromagnetic CMO. Experiment and theory agree that the ferromagnetism is confined to the first unit cell of CMO. At the (111) CRO/CMO interface, emergent ferromagnetism is observed but with a comparably enhanced moment. Transmission electron microscopy, atomic force microscopy, and x-ray reflectivity indicate smooth, atomically sharp interfaces in the superlattices. SQUID magnetometry confirms emergent ferromagnetism with an increase in magnetic moment to 2.8 µB/interfacial Mn compared to the 1 µB/interfacial Mn found in previous (001) superlattices. Transport measurements show a hysteretic anomalous Hall effect below the observed Curie temp (TC = 150 K) and a surprising change from n- to p-type carriers near Tc. Ab initio calculations indicate that the conductive CRO contributes to an additional magnetic moment. Thus, emergent ferromagnetism at (111) interfaces can be explained through charge transfer from CRO to CMO and proximity induced ferromagnetism in the CRO. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B53.00012: Nansocale imaging of antiferromagnetic domains in epitaxial Cr2O3 films using diamond quantum sensing microscopy Adam Erickson, Ather Mahmood, Syed Qamar Abbas Shah, Rupak Timalsina, Christian Binek, Abdelghani Laraoui Magnetic microscopy using nitrogen vacancy (NV) centers in diamond has become a versatile tool to study magnetic phenomena at the nanoscale [1]. In this study we use NV microscopy to map magnetic domains in antiferromagnetic (AFM) epitaxial Cr2O3 films. Cr2O3 thin films have been used to realize voltage-controlled AFM spintronics utilizing the peculiar boundary magnetization of single domains [2]. Boron doping can increase the Néel temperature of Cr2O3 to above 400 K and allow Voltage controlled Néel vector 900-rotation in zero magnetic field [3]. We present a detailed investigation of magnetic domains configuration in pure 200-nm thick Cr2O3 grown via pulsed laser deposition on Al2O3. Our study shows unique magnetic-domain structures similar to the granular Cr2O3 films [4]. We perform magnetic-field cooling measurements (heating above Néel temperature, then cooling under an applied field > 0.4 T) and measure the new magnetic domain configuration. We discuss plans to measure the dynamic domain wall evolution on voltage-induced domain reversal in pure and B doped films. [1] F. Casola, et al., Nat. Rev. Mat. 3, 17088 (2018). [2] N. Wu, et al., Phys. Rev. Lett. 106, 087202 (2011). [3] A. Mahmood, et al. Nat. Comms. 12, 1674 (2021). [4] P. Appel, et al., Nano Lett. 19, 1682 (2019). |
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