Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session B23: Controlling Magnetism in Oxide Heterostructures IFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP DCOMP Chair: Ryan Need, Univ of California - Santa Barbara Room: LACC 402B |
Monday, March 5, 2018 11:15AM - 11:27AM |
B23.00001: Electronic properties of doped and defective NiO – perspectives from quantum Monte Carlo and density functional theory Olle Heinonen, Hyeondeok Shin, Ye Luo, Panchapakesan Ganesh, Janakiraman Balachandran, Jaron Krogel, Anouar Benali, Paul Kent NiO is a Mott (or charge-transfer) insulator and is difficult to describe using density functional theory (DFT). Doped Mott insulators such as NiO are of interest for various applications, but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge- and spin-structures of NiO with various point defects, such as vacancies or substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than for a Ni vacancy, making potassium an attractive monovalent dopant for NiO. We compare our results with DFT results that include an on-site Hubbard U (DFT+U) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. This implies that schemes such as DFT+U are unlikely to capture responses that depend in subtle and complex ways on ground state properties such as charge and spin densities. |
Monday, March 5, 2018 11:27AM - 11:39AM |
B23.00002: Spin - Phonon Coupling in thin film NiO: UV and Visible Raman Spectroscopy Investigation Ece Aytan, Fariborz Kargar, Junxue Li, Weiwei Lin, Bishwajit Debnath, Roger Lake, Chia-Ling Chien, Jing Shi, Alexander Balandin Nickel oxide (NiO) is an antiferromagnetic insulator with a crystalline structure consisting of ferromagnetically aligned (111) planes. This material has recently attracted significant attention owing to proposals for spintronic applications in the THz frequency regime. Raman spectroscopy can provide valuable information on the phonon and magnon states in such materials, and can possibly shed light on specifics of the phonon – magnon interactions. Here, we report a comparative Raman spectroscopic investigation of (111)-oriented NiO single crystals and NiO(111) thin films under ultraviolet (UV) and visible laser excitations, and we compare the bulk results with thin film results to explore the dimension effect. The measurements were conducted in the backscattering configuration under the laser excitation wavelength of 325 nm (resonant) and 488 nm (non-resonant). M. M. Lacerda et al., APL. 110, 202406 (2017). |
Monday, March 5, 2018 11:39AM - 11:51AM |
B23.00003: Coercive Field Enhancement in Microstructured (La1-yPry)1-xCaxMnO3 thin films Ashkan Paykar, Ambika Shakya, Amlan Biswas (La1-yPry)1-xCaxMnO3 (LPCMO) is a perovskite material with complex electronic and magnetic behaviors because of phase competition between its ferromagnetic metallic (FMM) phase and charged order insulating (COI) phase. LPCMO thin films also exhibit unique magnet behavior due to the additional effects of substrate-induced strain such as single-domain to multi-domain transition as a function of temperature. LPCMO thin films were deposited on NdGaO3 (NGO) substrates using pulsed laser deposition. These thin films were then patterned into an array of 100 µm squares using photolithography. We observed that the coercive field increased by a factor of about 4 due to the patterned microstructure. This coercive field enhancement is due to magnetic interactions between the isolated LPCMO regions mediated by the paramagnetic NGO substrate. We will also discuss the effects on the coercive field due to increasing the gap between the patterned squares in the array. |
Monday, March 5, 2018 11:51AM - 12:03PM |
B23.00004: Ultrafast Electron Diffraction on a Magnetoresistive Manganite Anshul Kogar, Alfred Zong, Timm Rohwer, Di Lu, Seung Sae Hong, Harold Hwang, Nuh Gedik Manganite compounds are known to host peculiar behavior such as colossal magnetoresistance, Jahn-Teller polarons and phase separation among other phenomena. In this experiment, we perform ultrafast electron diffraction experiments on freestanding La0.7Sr0.3MnO3 thin films. Ultrafast electron diffraction is a technique whereby an incident ultrafast pump pulse excites the sample into a non-equilibrium state and a probe pulse follows shortly thereafter, examining how the structure of the sample changes after excitation as a function of time delay. In this study, we observe that following the pump pulse, Bragg peaks show anomalous behavior in the form of enhanced coherence on a timescale of approximately 100 picoseconds. These results are discussed in terms of the melting of Jahn-Teller polarons. |
Monday, March 5, 2018 12:03PM - 12:15PM |
B23.00005: Electronic Excitations of Strained LaCoO3 Thin Films Investigated by Resonant Inelastic X-ray Scattering Ting-Chun Huang, Hsiao-Yu Huang, Amol Singh, Jun Okamoto, Ashish Chainani, Ying-Hao Chu, C. Chen, Di-Jing Huang The spin-state transition of perovskite LaCoO3 is an interest and important subject, which has received much attention for decades. Here we present measurements of high-resolution resonant inelastic X-ray scattering (RIXS) at Co L-edge on LaCoO3 thin films grown on LSAT substrates of various orientations, including (110) and (111), by pulse laser deposition. The change in the magnetic transition of LaCoO3 thin films shows that magnetic structure is sensitive to tensile-strain. We will present RIXS results to discuss the change of dd excitations and related elementary electronic excitations in response to different tensile-strain in the thin films. Our data provide an effective method to quantify the ratio of high-spin and and low-spin states in the thin films. |
Monday, March 5, 2018 12:15PM - 12:27PM |
B23.00006: Strain-induced phase arrangement in LaVO3 thin films Jason Lapano, Matthew Brahlek, Jacob Ruff, Nouamane Laanait, John Freeland, Roman Engel-Herbert The perovskite oxide LaVO3 is an archetypical Mott insulator which undergoes a antiferromagnetic (AFM) orbital and spin order transition at ~140 K, concomitant with a structural distortion from the high temperature Pbnm structure 1. In this talk, we report on the arrangement of coexisting phases stabilized by epitaxial strain imposed by the substrate using a combination of synchrotron x-ray diffraction2, x-ray diffraction microscopy3 and scanning transmission electron microscopy. Coherently strained LaVO3 thin films were grown by hybrid molecular beam epitaxy (hMBE)4 on NdGaO3 and GdScO3. It is found that different order and phase arrangement occurs at room temperature and low temperatures at dramatically different length scales ranging from about 3 nm to 300 nm. We discuss the nature and origin of these ordered phases, which have not been observed in bulk LaVO3, in light of the structural constraints imposed by the substrate. |
Monday, March 5, 2018 12:27PM - 12:39PM |
B23.00007: Epitaxial growth of high quality SrFeO3 films on (001) oriented (LaAlO3)0.3(Sr2TaAlO6)0.7 Deshun Hong, Changjiang Liu, John Pearson, Anand Bhattacharya Growth of SrFeO3 films with stoichiometry of (1:1:3) is challenging as the unstable Fe4+ oxidation state favors the formation of O vacancies. Here, we report layer by layer growth of SrFeO3 on (001) oriented LSAT using ozone assisted molecular beam epitaxy. Upon cooling from room temperature, the film's resistivity is as low as the best single crystals, with two identifiable transition points near 110 K and 60 K in resistivity measurements, being hysteretic between cooling and warming through the 60 K transition. During various annealing steps, the low temperature resistivity changes by orders of magnitude, accompanied by an increase in the c-axis lattice parameter. The hysteresis near 60 K persists for a wide range of annealing conditions. We have identified conditions where changes due to annealing can be reversed. We attribute resistiviy and lattice changes to the reversible movement of oxygen. Thus, SrFeO3 may be a promising material for resistive memory . |
Monday, March 5, 2018 12:39PM - 12:51PM |
B23.00008: Ultralow Damping in Epitaxial Spinel Ferrite Thin Films Satoru Emori, Di Yi, Samuel Crossley, Jacob Wisser, Purnima Balakrishnan, Padraic Shafer, Christoph Klewe, Alpha N'Diaye, Brittany Urwin, Krishnamurthy Mahalingam, Brandon Howe, Harold Hwang, Elke Arenholz, Yuri Suzuki Magnetic insulator thin films are expected to be excellent media for spin-based information without charge flow. This expectation relies on the premise that magnetic insulators exhibit lower magnetic damping compared to their metallic counterparts. However, insulating behavior is not a sufficient requirement for low damping, as evidenced by the very limited options for low-damping magnetic insulators. In this presentation, we demonstrate a new class of ultralow-damping insulator based on design criteria minimizing orbital angular momentum as well as crystalline and cation valence disorder. Specifically, we show ultralow damping in spinel structure magnesium aluminum ferrite (MAFO), in which magnetization arises solely from Fe3+ ions with zero orbital angular momentum. Epitaxial MAFO films with thicknesses <20 nm exhibit ferromagnetic resonance linewidths of ≈0.6 mT around 10 GHz and Gilbert damping parameters of ≈0.0015. Our findings demonstrate that minimal spin-orbit coupling and coherent epitaxy allow for ultralow damping in ferrite thin films, expanding the materials choices for energy-efficient insulator spintronics. |
Monday, March 5, 2018 12:51PM - 1:03PM |
B23.00009: Designing global and local magnetic phases with uniaxial lattice expansion Thomas Ward, Andreas Herklotz, Yogesh Sharma Epitaxy and/or isovalent substitutions are widely used to modify the internal lattice energies that control magnetic phase composition in strongly correlated transition metal oxides (TMO). However, these techniques do not allow for continuous and fine command over structural properties post-growth which hampers our ability to systematically study structure-function relationships. We will present our recent work which relies on low energy helium ion implantation to control uniaxial lattice expansion post-growth to bypass these limitations in epitaxial manganites and nickelates thin films. This strategy is shown to provide a means to control orbital degeneracies which can then be exploited to alter magnetic character of TMOs. Magnetic anisotropy, magnetic ordering type, and magnetic onset temperatures can all be controlled. Further, local application of strain doping allows one to design coexisting magnetic phases of vastly different character into a single crystal wafer. |
Monday, March 5, 2018 1:03PM - 1:39PM |
B23.00010: Electronic properties of nickelate based films and heterostructures Invited Speaker: Jean-Marc Triscone Perovskite nickelates (RNiO3, RE = Rare Earth) are fascinating materials, well-known for their metal to insulator transition (MIT) and unique antiferromagnetic (AFM) ground state [1]. In this talk, I will discuss the electronic and magnetic properties of [001] LaNiO3 and (La1-xNdx)NiO3 films [2]. In the latter, the Nd content allows the MIT temperature to be controlled. Particular attention will be paid to samples with an MIT close to 0K. I will also discuss the properties of [001] (SmNiO3)/(NdNiO3) and (LaNiO3)/(LaMnO3) superlattices [3,4]. The former display a single or a double MIT depending on the structure wavelength. In the latter system, an unusual exchange bias and antiferromagnetic interlayer exchange coupling are observed in [111]-oriented (LaNiO3)/(LaMnO3) superlattices [3,4]. |
Monday, March 5, 2018 1:39PM - 1:51PM |
B23.00011: Nernst effect measurements on LaNiO3 grown by molecular beam epitaxy Changjiang Liu, Friederike Wrobel, Deshun Hong, Jason Hoffman, John Pearson, Anand Bhattacharya Perovskite LaNiO3 is a correlated metal, the only member in the ReNiO3 (Re = Rare earth) series showing metallic behavior down to the lowest temperatures. Recently, LaNiO3 has received renewed attention due to advancements in growth techniques for producing high quality bulk single crystal samples with very low resistivities, leading also to a re-examination of the magnetic properties of LaNiO3. In this work, we report on Nernst effect measurements on LaNiO3 thin films grown by ozone-assisted molecular beam epitaxy. The films have a resistivity of ~ 16 µΩ cm at T = 2 K with a residual resistivity ratio (R(300 K)/R(2 K)) > 8. Hall measurements indicate that the majority charge carriers are hole like, with an increasing Hall slope as temperature decreases. In the Nernst signal, there is a sign change at low temperatures, which is unusual. This phenomenon combined with other transport measurements will be discussed in the context of what is known about the electronic and magnetic properties of this correlated metal. |
Monday, March 5, 2018 1:51PM - 2:03PM |
B23.00012: Thickness Dependent Metal-Insulator Transition in (111) LaNiO3 Thin Films Margaret Kane, Charles Flint, Di Yi, Arturas Vailionis, Yuri Suzuki LaNiO3 is the only metallic rare earth nickelate, but a metal-insulator transition can be induced as a function of thickness in LaNiO3 films. Some proposed mechanisms for this behavior include charge disproportionation, symmetry changes, and order-disorder transition. To better understand this metal-insulator transition, we synthesized (111)-oriented LaNiO3 films of various thicknesses on (111)-oriented LaAlO3 substrates in layer-by-layer mode by interval pulsed laser deposition. In contrast to the 2-4 unit cell transition thickness seen in most (001) LaNiO3 films studied thus far, we have found the onset of insulating behavior in (111) LaNiO3 to occur at 6 unit cells. Atomic force microscopy shows typical rms roughness of < 0.2 nm and X-ray diffraction confirms excellent crystallinity. X-ray absorption spectroscopy indicates the presence of Ni2+ in the thinnest insulating films while thicker metallic films are primarily Ni3+. The correlation of Ni2+ with insulating behavior in (111) and (001) films suggests charge disproportionation might play a significant role in the metal-insulator transition. The tilts and deformations of the NiO6 octahedra in the strained (111) films likely also affect the onset of the metal-insulator transition. |
Monday, March 5, 2018 2:03PM - 2:15PM |
B23.00013: Paramagnetic to Antiferromagnetic Phase Transition in Non-Fermi Liquid Perovskites Induced by Strong Electronic Correlation Z. S. Lim, Ariando Ariando A fourfold symmetric in-plane anisotropic magnetoresistance (AMR) is consistently measured from CaIrO3 perovskite thin films grown on SrTiO3(001) substrate, whose bulk property is known to be a paramagnetic semimetal. We demonstrate that the origin of this AMR signal is a spin-flop of antiferromagnetic phase in the localization regime of this material, which is supported by magnetometry data. We further discuss the fourfold symmetric in-plane AMR to be a universal behaviour observable from other perovskite compounds having neighbouring properties with CaIrO3 when those materials are grown into ultrathin films to reach the localization regime. This work provides an experimental linkage between AMR and the tuning of quantum critical phase transition by electron-electron correlations. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700