Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X43: Defects and Structural Control in Magnetic Oxide HeterostructuresFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP DCOMP Chair: Suzanne te Velthuis, Argonne National Laboratory Room: 390 |
Friday, March 17, 2017 8:00AM - 8:12AM |
X43.00001: Magnetic domains and magneto-optic responsivity of bismuth-doped iron garnet films Dong Ho Wu, Mannix Shinn It is well known that diamagnetic dilution of iron (Fe) and gallium (Ga) in bismuth-doped iron garnet materials increases the Faraday rotation response (i.e. magneto-optic responsivity). However, our experiments indicate that such enhancement of the magneto-optic (MO) responsivity is a macroscopically averaged effect. Careful MO responsivity measurements at a magnetic field exceeding a certain critical field $H_{c}$, reveal Barkhausen steps, a step-like responsivity curve which is due to pinning effect in the domain walls. The critical field $H_{c}$ varies sensitively even with a slight change of Fe and Ga in the MO material. Also, our polarization microscopy indicates the magnetic domain structure seems to be sensitively dependent on the chemical content of the MO material. We suspect that the variation of the chemical composition alters chemical inhomogeneities and stress in the MO crystal, leading to drastic changes in pinning sites and the domain wall behavior. We will present our experimental results on the magnetic domain behavior and the magneto-optic responsivity as a function of the chemical components. [Preview Abstract] |
Friday, March 17, 2017 8:12AM - 8:24AM |
X43.00002: Cation Valence Control in La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$Co$_{\mathrm{0.5}}$Mn$_{\mathrm{0.5}}$O$_{\mathrm{3}}$ Thin Films and Bilayers Alex Kane, Rajesh Chopdekar, Elke Arenholz, Apurva Mehta, Yayoi Takamura The unique interplay between spin, orbital, charge, and lattice degrees of freedom at interfaces in perovskite oxides makes them model systems to probe and exert magnetic control at the nanoscale. Previous work revealed exchange coupling in bilayers composed of a hard ferromagnetic (FM) La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$CoO$_{\mathrm{3}}$ (LSCO) layer and a soft FM La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ (LSMO) layer, coincident with charge transfer across the LSCO/LSMO interface. An interfacial Co$^{\mathrm{2+}}$-rich LSCO layer produced a FM superexchange interaction with Mn$^{\mathrm{4+}}$ ions in the adjacent LSMO layer, [1] mimicking the behavior of ordered Co$^{\mathrm{2+}}$/Mn$^{\mathrm{4+\thinspace }}$ions in the double perovskite La$_{\mathrm{2}}$CoMnO$_{\mathrm{6}}$ [2]. In an attempt to manipulate the extent of charge transfer in this system, La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$Co$_{\mathrm{0.5}}$Mn$_{\mathrm{0.5}}$O$_{\mathrm{3}}$ (LSCMO)/LSMO and LSCMO/LSCO bilayers were deposited by pulsed laser deposition. Bulk magnetometry and soft x-ray magnetic spectroscopy were used to investigate the Mn/Co magnetic and electronic structures, comparing the surface/interface dominant effects vs. the film average. The LSCMO/LSMO bilayer enhanced the magnetically soft Co$^{\mathrm{2+}}$ population at the interface, while the LSCMO/LSCO bilayers strongly suppressed the Co$^{\mathrm{2+}}$ state in the LSCMO layer. [1] B. Li, et. al., APL. 105, 202401 (2014) [2] R. I. Dass and J. B. Goodenough, PRB, 67, 014401 (2003) [Preview Abstract] |
Friday, March 17, 2017 8:24AM - 8:36AM |
X43.00003: External tuning of the spin state of oxygen vacancies at strontium titanate surfaces Oleg Brovko, Erio Tosatti Among the wealth of optical, electronic and magnetic phenomena induced in strontium titanate $\mathrm{(SrTiO_3)}$ bulk or at its surface by vacancies or dopants, oxygen-vacancy-induced magnetism remains one of the most studied yet still one of the least understood ones. Here we use density functional theory to explore the possibility of dynamically switching the multiplet state of an oxygen vacancy or a vacancy cluster at ideal and reconstructed $\mathrm{SrTiO_3}$ surfaces by external stimuli such as charge injection, electric bias or tip-induced force fields. We relate the mechanism responsible for the change in the spin state to charge redistribution at the vacancy site. Since each state change should imply, as for a quantum dot, a dissipation channel for the external agent, these ideas can be tested experimentally, e.g. within the scope of atomic force microscopy at low temperatures. [Preview Abstract] |
Friday, March 17, 2017 8:36AM - 8:48AM |
X43.00004: Striped lanthanum cobaltite films: how strain orders oxygen defects Axiel Yael Birenbaum, Michael D. Biegalski, Liang Qiao, Valentino R. Cooper, Albina Borisevich Oxygen-deficient metal cobalt oxides have been widely studied for solid oxide fuel cell cathode applications. In order to predict atomic-scale transport pathways, a thorough understanding of its defect properties is crucial. Previous studies, including Scanning Transmission Electron Microscopy (STEM), demonstrate lanthanum cobaltite, grown as thin films on [100]$_{pc}$ oriented perovskites, spontaneously order its oxygen vacancies. In this work, we investigate the behavior of $\rm LaCoO_{3-\delta}$ thin films grown on $\rm SrTiO_3$ [111] surface to determine if orientation can be used to shape the anisotropy of oxygen transport. For these films, STEM studies reveal ordered vacancy arrangements. We do so by establishing the structural and electronic properties of $\rm LaCoO_{3-\delta}$ on $\rm SrTiO_3$, using ab initio electronic structure calculations. We then treat how epitaxial strain leads to oxygen vacancies forming these distinctive stripe patterns. The impact of different substrates is addressed. In addition, this leads to an opportunity to discuss the effect of reduced symmetry in oxygen deficient compounds on cobalt oxide behavior compared to the ideal perovskite environment. [Preview Abstract] |
Friday, March 17, 2017 8:48AM - 9:00AM |
X43.00005: Coupling and competition between ferroelectricity, magnetism, strain and oxygen vacancies in AMnO$_{\mathrm{3}}$ perovskites Astrid Marthinsen, Sverre Magnus Selbach First-principles calculations based on density functional theory is employed to investigate the interplay between oxygen vacancies, $A$-site cation size, epitaxial strain in the 001 plane, ferroelectricity and magnetism in the perovskite manganite series, $A$MnO$_{\mathrm{3}}$ ($A=$Ca$^{\mathrm{2+}}$, Sr$^{\mathrm{2+}}$, Ba$^{\mathrm{2+}})$. Increasing the unit cell volume through either chemical pressure or tensile strain generally lowers the formation energy of neutral oxygen vacancies. Increased volume also favors polar distortions, both because competing rotations of the oxygen octahedra are suppressed and because Coulomb repulsion associated with cation off-centering is reduced. Ferroelectric polarization favors ferromagnetism over antiferromagnetism as the polar distortion bends the Mn-O-Mn bond angles away from the optimal 180$^{\mathrm{o}}$. Polar distortions compete with the formation of oxygen vacancies, which have a higher formation energy in the polar phases; conversely the presence of oxygen vacancies suppresses the onset of polarization. In contrast, oxygen vacancy formation energies are lower for ferromagnetic than antiferromagnetic order. Our findings suggest a rich and complex phase diagram, in which defect chemistry, polarization, structure and magnetism can be modified using $p$O$_{\mathrm{2}}$, strain, and electric or magnetic fields. [Preview Abstract] |
Friday, March 17, 2017 9:00AM - 9:12AM |
X43.00006: Imaging oxygen vacancies in EuO$_{1-x\, }$using Scanning Tunneling Microscopy and Spectroscopy Aaron Wang, Gaurab Rimal, Jinke Tang, TeYu Chien EuO$_{1-x}$, a ferromagnetic semiconductor, attracts plenty of attention due to its unique magnetic properties, such as the possible existence of the magnetic polarons and skyrmions. Here we present a scanning tunneling microscopy and spectroscopy study of the EuO$_{1-x}$ thin film made by pulsed laser deposition. After an ultra-high vacuum sputtering followed by a 300 $^{o}$C annealing, the topography and d$I$/d$V$ mapping of the EuO$_{1-x}$ were successfully measured. Interestingly, in d$I$/d$V$ mapping, around 5 nm sizes dot-like features with higher d$I$/d$V$ contrast were observed. The observed dot-like features were sparsely and uniformly distributed over the measured surfaces. After further annealing at 500 $^{o}$C for another 30 minutes, the number of the dot-like features in d$I$/d$V$ mapping increased to overlap each other, indicating the dot-like features are most likely related to the oxygen vacancies created by vacuum annealing. The d$I$/d$V$ spectra inside and outside of the dot-like features showed similar bandgap but distinct spectral weight in both valence and conduction bands. This work paves the road for further STM study on this intriguing material. [Preview Abstract] |
Friday, March 17, 2017 9:12AM - 9:24AM |
X43.00007: Tracking BO$_{\mathrm{6}}$ Coupling in Perovskite Superlattices to Engineer Magnetic Interface Behavior Albina Borisevich, Qian He, Saurabh Ghosh, Eun Ju Moon, Steve May, Andrew Lupini, Sokrates Pantelides In the past several years, control of BO$_{\mathrm{6}}$ octahedral coupling at ABO$_{\mathrm{3\thinspace }}$perovskite interfaces has emerged as a new tool for engineering of interface properties due to its strong coupling to polar and magnetic properties. High resolution data on tilt transitions at interfaces is instrumental for evaluating the validity of existing theoretical models and developing predictive theories. Recently, we have developed a unique method to investigate BO$_{\mathrm{6}}$ rotation patterns in complex oxides with unit cell resolution. Our method involves column shape analysis in ABF-STEM images of the perovskite heterointerfaces taken in specific orientations. This method will allow us to determine local symmetry between adjacent unit cells, revealing the BO$_{\mathrm{6}}$ coupling behavior at heterointerfaces in 3D. This technique was used to characterize structure and predict properties via a combined STEM and DFT study of magnetic superlattice of La(Ca)MnO$_{\mathrm{3}}$/La(Sr)MnO$_{\mathrm{3}}$ with different periodicities, which exhibit a range of electromagnetic coupling behaviors. We will also discuss the prospects for tilted structure determination using electron ptychography. The correlations among the BO$_{\mathrm{6}}$ rotation, domain size, superlattice periodicity and the electromagnetic coupling will be discussed in detail. [Preview Abstract] |
Friday, March 17, 2017 9:24AM - 10:00AM |
X43.00008: Interface engineering of metal-oxygen bonds as a new route for exploring functional properties of transition metal oxides Invited Speaker: Daisuke Kan Metal-oxygen bonds in transition-metal oxides are responsible for a broad spectrum of functional properties, and atomic-level control of the bonds is a key for developing future oxide-based electronics. Artificial heterostructures with chemically abrupt interfaces consisting of dissimilar oxides have provided a good platform for engineering novel bonding geometries that could lead to emergent phenomena not seen in bulk oxides. Here we show that the Ru-O bonds (or oxygen coordination environments) of a perovskite, SrRuO$_{\mathrm{3}}$, can be controlled by heterostructuring SrRuO$_{\mathrm{3}}$ with a thin (0--4 monolayers thick) Ca$_{\mathrm{0.5}}$Sr$_{\mathrm{0.5}}$TiO$_{\mathrm{3}}$ layer grown on GdScO$_{\mathrm{3}}$ substrates [1]. We found that a Ru-O-Ti bond angle characterizing the SrRuO$_{\mathrm{3}}$/Ca$_{\mathrm{0.5}}$Sr$_{\mathrm{0.5}}$TiO$_{\mathrm{3}}$ interface structure can be engineered by layer-by-layer control of the Ca$_{\mathrm{0.5}}$Sr$_{\mathrm{0.5}}$TiO$_{\mathrm{3}}$ layer thickness, and that the engineered Ru-O-Ti bond angle not only stabilizes a Ru-O-Ru bond angle never seen in bulk SrRuO$_{\mathrm{3}}$ but also tunes the magnetic anisotropy in the entire SrRuO$_{\mathrm{3}}$ layer. The results demonstrate that interface engineering of the metal-oxygen bonds is a good way to control additional degrees of freedom in designing functional oxide heterostructures. [1] D. Kan et al Nature Materials 15, 432 (2016). [Preview Abstract] |
Friday, March 17, 2017 10:00AM - 10:12AM |
X43.00009: Probing tailored octahedral modulations in isovalent manganite superlattices with standing-wave-excited angle-resolved photoemission Weibing Yang, Ravini Chandrasena, Eun Ju Moon, Arian Arab, Vladimir Strokov, Steven May, Alexander Gray Tailoring and spatially-confining electronic and ferroic behavior via coherent epitaxy offers a promising avenue towards engineering new functional properties in complex oxide heterostructures [1]. Here we utilize soft x-ray standing-wave photoemission spectroscopy to non-destructively probe depth-dependent electronic structure of isovalent manganite superlattices wherein the electronic and magnetic properties are modulated with depth via O octahedra rotations. Standing-wave-excited spectroscopy of the Mn 2p and O 1s core-levels confirms isovalent nature of the Mn ions in the superlattice and reveals significant depth-dependent variations in the local chemical and electronic environment around the O atoms consistent with rotational modulations of the O octahedra. Momentum-resolved standing-wave spectroscopy reveals modulations in the valence-band dispersion of the strongly-hybridized Mn and O states. \newline [1] E. J. Moon et al., Nature Comm. 5, 5710 (2014). [Preview Abstract] |
Friday, March 17, 2017 10:12AM - 10:24AM |
X43.00010: Investigation of magnetic interactions at Y$_{3}$Fe$_{5}$O$_{12}$/Gd$_{3}$Ga$_{5}$O$_{12}$ interface by inserting a diamagnetic Y$_{3}$Sc$_{2}$Al$_{3}$O$_{12}$ buffer layer Yang Cheng, Aidan Lee, Muqing Yu, Jack Brangham, Fengyuan Yang Y$_{3}$Fe$_{5}$O$_{12}$ (YIG) is a well-established material for microwave applications and pure spin transport. Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) is a widely used substrate for epitaxial YIG film growth with very small lattice mismatch. Based on our recent study showing enhanced magnetization in YIG films, we suspect the strong Gd moment in GGG may couple to YIG and affect ferromagnetic resonance spin pumping. To probe this effect, we selected a lattice-matched diamagnetic buffer layer, Y$_{3}$Sc$_{2}$Al$_{3}$O$_{12}$ (YSAG), to decouple the potential magnetic interaction between YIG and GGG. Phase-pure YSAG powder, prepared by sol-gel synthesis, was made into a target for epitaxial growth of YSAG films on GGG using off-axis sputtering. X-ray diffraction revealed clear Laue oscillations and a narrow YSAG rocking curve of FWHM 0.0074 degrees, demonstrating high crystalline quality. In addition, the in-plane lattice constant of YSAG films is within 0.1{\%} to those of GGG and YIG, making it an ideal buffer layer for this study. We then grow YIG films on YSAG buffered GGG, which show similarly high crystalline quality and ferromagnetic resonance properties to YIG films on GGG. We will also discuss dynamic spin transport studies using YIG/YSAG/GGG. [Preview Abstract] |
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