Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G6: Focus Session: Magnetic Oxide Thin Films and Heterostructures: Strain Effects |
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Sponsoring Units: DMP GMAG Chair: Christian Urban, University of California, San Diego Room: 108 |
Tuesday, March 4, 2014 11:15AM - 11:51AM |
G6.00001: Anion-based approaches to tunable functionality in oxide heterostructures Invited Speaker: Steven May The ability to control the position and composition of the anion site is emerging as a promising route to tune properties in epitaxial perovskites. This talk will focus on recent and ongoing efforts aimed at developing anion-based approaches to tailor electronic and magnetic properties in oxide films. First, I will discuss how the position of the oxygen anions can be tailored to stabilize non-bulk-like bond angles and lengths, thereby altering electronic bandwidth. Recent work on La$_{2/3}$Sr$_{1/3}$MnO$_3$ will be presented in which ultrathin films under the same strain state exhibit dramatically different electronic and magnetic properties when grown on substrates with different symmetries. In the second half of the talk, I will describe efforts focused on altering the composition of the anion site. In La$_{1/3}$Sr$_{2/3}$FeO$_{3-\delta}$ films, a reversible change in oxygen content leads to dramatic changes in electrical, optical, and structural properties. Finally, the synthesis of oxyfluoride ferrite and nickelate perovskite films via topotactic reactions carried out following thin film deposition will be described. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G6.00002: The effect of uniaxial strain versus chemical doping on V$_{2}$O$_{3}$ thin films Christian Urban, Ivan Schuller Vanadium(III) oxide (V$_{2}$O$_{3})$ exhibits as a function of temperature a metal-insulator transition associated with a structural and a magnetic transition which can be influenced either by strain or chemical doping. We investigate the effect of doping and external pressure on V2O3 thin films. Due to the thin film geometry, application of pressure results in a uniaxial strain perpendicular to the surface. In contrast, chemical doping causes isotropic strain. The interplay of the different strains is reflected in the electrical transport behavior throughout the phase transition. Doping with Ti and Cr is employed in highly oriented films to cover a large portion of the phase diagram. Application of external pressure on doped films tests the commonly unquestioned equivalence of doping and pressure. Additionally, we investigate the interplay of doping and pressure on the transition temperature and transport properties. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G6.00003: Magnetic Excitations in Thin Film Ba2IrO4 and Sr2IrO4 Probed by Resonant Inelastic X-ray Scattering J.P. Clancy, A. Lupascu, H. Gretarsson, M.H. Upton, J. Kim, Z. Islam, M. Uchida, D.G. Schlom, K.M. Shen, J. Nichols, J. Terzic, G. Cao, S.S.A. Seo, V.M. Katukuri, L. Hozoi, J. van den Brink, H. Stoll, Y.-J. Kim We have performed resonant inelastic x-ray scattering (RIXS) measurements on epitaxial thin film samples of the layered perovskite iridates Ba2IrO4 and Sr2IrO4. These materials display a novel Jeff = 1/2 Mott insulating ground state driven by strong 5d spin-orbit coupling effects. By studying 10 to 50 nm thin film samples grown on a variety of different substrates (GSO, STO, LSAT), we have investigated the impact of applied tensile/compressive strain on the characteristic magnetic and electronic excitations of these materials. Unlike other perturbations, such as doping or applied magnetic field, we find that applied strain does not alter the magnetic structure of Ba2IrO4 or Sr2IrO4. However, strain does affect the magnetic energy scales of these systems, providing a means of tuning both the ordering temperature (Tn) and the magnetic exchange interactions (J). In addition, we show that the dispersion of the low-lying magnon and spin-orbit exciton modes is renormalized by strain-induced structural changes. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G6.00004: Strain induced magnetization reversal in Ba$_2$IrO$_4$ via strong orbital-lattice coupling Choong H. Kim, Craig J. Fennie We have studied from first principles the structural, electronic, and magnetic properties of the layered-perovskite iridate Ba2IrO4 as a function of epitaxial strain. In contrary to what is usually assumed, we find within density functional theory that the ground state structure displays oxygen octahedra rotations ($\sim 6^\circ$ about the $c$-axis). This leads to a canting of the nominally antiferromagnetic moments. It turns out that the magnitude and direction of the orbital moment canting, which is in the opposite direction to the spin canting moment, can be controlled with strain. This leads to a situation in which the total magnetization can be tuned and in fact be reversed with strain. Our observations highlight a difficulty with describing magnetism in Ba$_2$IrO$_4$ within a simple effective $j_{\rm eff}$-spin Hamiltonian. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G6.00005: Influence of the SrTiO$_{3}$ Phase Transformation on Magnetotransport Phenomena in Ultrathin SrTiO$_{3}$(001) / La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$ Srinivas Polisetty, Shameek Bose, Shun Wang, Chris Leighton The existence of electronic and magnetic ``dead layers'' at interfaces in complex oxide heterostructures presents a significant challenge to the realization of functional oxide devices. Our recent work on La$_{0.5}$Sr$_{0.5}$CoO$_{3-\delta}$ (LSCO) [1,2] has shown that the formation of these ``dead layers'' in cobaltites is due to strain-induced oxygen vacancy formation and ordering. Here, we present some of the remarkable array of complex magnetotransport phenomena that accompany this interfacial magnetic inhomogeneity in SrTiO$_{3}$(001)/LSCO. Reduction of the film thickness from 70 to 30 {\AA} results in a percolative metal-insulator transition, the onset of large magnetoresistance due to inter-cluster transport, and clear signatures of the 108 K cubic-tetragonal phase transition in the SrTiO$_{3}$. The latter include resistivity anomalies at 108 K, strong temperature hysteresis, in-plane anisotropy, and stochastic discontinuities in resistivity [3]. We attribute these effects to strain-mediated propagation of the substrate phase transformation into the pseudomorphic LSCO and argue that the interplay between this effect and the thickness evolution of the magnetic inhomogeneity provides qualitative understanding of all observed phenomena. \\[4pt] [1] Torija \textit{et al.}, Adv. Mater. \textbf{23}, 2711 (2011).\\[0pt] [2] Gazquez \textit{et al.}, APL Mater. \textbf{1}, 012105 (2013).\\[0pt] [3] Polisetty \textit{et al.} (\textit{unpublished)}. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G6.00006: Making Nonmagnetic Palladium Ferromagnetic by Antiferromagnetic CoO Srijan Kumar Saha, Piotr Ku\'{s}wik, Pedro L. Gastelois, Marek Przybylski, Valeri Stepanyuk, J\"urgen Kirschner We present a novel finding of our combined experimental and theoretical studies which have revealed unexpected spin polarization of the Pd(001) substrate in contact with antiferromagnetic CoO overlayers. We give an evidence that the ferromagnetism of Pd is caused by the zigzag positions of Co atoms with respect to the Pd interface, resulted from the lattice-mismatch driven structural relaxation. Thanks to the itinerant nature of its 4d electrons, we see that the ferromagnetic properties of Pd are highly sensitive to the local environment and can be enhanced further by increasing the thickness of CoO overlayer film or/and by applying an additional uniaxial pressure along c-axis exerted externally on the bottom layers of the Pd substrate. Our finding provides new functionality for the interfacial moments of the CoO/Pd system, which can be accessed experimentally, e.g., by the magneto-optical Kerr effect as we demonstrate here. [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G6.00007: Enhancement of Curie temperature in thin-films of SrRuO$_{3}$ Sean Thomas, Bouwe Kuiper, Jun Hu, Zhicheng Zong, Ruqian Wu, Guus Rindjers, Gertjan Koster, Jing Xia SrRuO$_{3}$ (SRO) is an itinerant ferromagnet that has generated a large amount of interest due to its potential use as an electrode layer in complex oxide heterostructures. We present the results of our ongoing study of the ferromagnetic properties of thin-films of SRO, which have been measured using a scanning Sagnac microscope. By varying the thickness of the a non-ferromagnetic capping-layer, we have observed enhancement of the Curie temperature of over 20 K as compared to uncapped films of the same thickness. The amount of enhancement can be tuned by varying the thickness of the capping-layer. Further, we have performed density functional theory calculations that suggest the enhancement may be due to rotations of the oxygen octahedrons in the SRO near the interface between the SRO and capping-layer. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G6.00008: Strain-dependent, Extraordinary Magnetocrystalline Anisotropy in Sr$_{2}$CrReO$_{6}$ Epitaxial Films Jeremy Lucy, Jennifer Soliz, Molly Ball, Oscar Restrepo, Wolfgang Windl, Patrick Woodward, Fengyuan Yang, Adam Hauser, John Freeland We have grown Sr$_{2}$CrReO$_{6}$ films that exhibit one of the largest anisotropy fields shown to date (18.1 T) and a large uniaxial magnetocrystalline anisotropy energy $K_{u} =$ 9.05 $\times$ 10$^{6}$ erg/cm$^{3}$. We investigate strain-controlled magnetocrystalline anisotropy for epitaxial Sr$_{2}$CrReO$_{6}$ films grown on (LaAlO$_{3})_{0.3}$(Sr$_{2}$AlTaO$_{6})_{0.7}$, SrTiO$_{3}$ and Sr$_{2}$CrNbO$_{6}$/LSAT substrates using high resolution X-ray diffraction, in-plane and out-of-plane superconducting quantum interference device magnetometry, and density functional theory calculations. The substrates impose tetragonal distortions of $c$/$a =$ 1.025, 1.007 and 0.991, respectively, which lead to dramatic changes in magnetocrystalline anisotropy of order tens of tesla and a switching of the magnetic easy axis from in-plane for compressive strain to out-of-plane for tensile strain, as observed via magnetometry measurements. Density functional theory calculations elucidate the dependence of oxygen octahedra tilting and rotation on tetragonal distortions, which affect both electronic and magnetic properties of the films. Finally, X-ray magnetic circular dichroism measurements reveal strong magnetic moment contributions at the oxygen sites, as evident in oxygen-specific X-ray absorption spectra. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G6.00009: Tunable strain-induced phase transitions in manganite thin films on BaTiO3 substrate Wengang Wei, Jinjie Chen, Kai Zhang, Zhang Du, Wenbin Wang, LiFeng Yin, Jian Shen The transport and magnetic properties of manganites depend sensitively on the lattice parameters, which can be conveniently tuned by the epitaxial strain in thin films. In an extreme case of manganites thin films grown on ferroelectric BaTiO3 (BTO), sudden jumps of both magnetization and resistivity have been observed upon cooling (or warming) in accordance with the temperature-dependent structural transitions of the BTO substrate. Surprisingly, both up and down jumps have been reported for both magnetization and resistivity of the LCMO films at the same temperature point where BTO undergoes a structural transition from orthorhombic to rhombohedra. Here we solve the puzzle by showing that the physical origins of the up and down jumps of both magnetization and resistivity are tied to the relative orientations of c-axis of the BTO substrate with respect to the LCMO film plane during the structural transition. Based on this understanding, we demonstrate the ability to control the up and down jumps by electric field poling of the BTO substrate upon cooling. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G6.00010: Strain induced ferromagnetism in LaCoO3 and interface coupling in magnetic multilayers Francisco Rivadulla, Beatriz Rivas-Murias, Irene Lucas, Pilar Cavero, Andrey Chuvilin, Luis Hueso, Luis Morell\'on Bulk LaCoO$_{3}$ (LCO) is rhombohedral with the Co$^{3+}$ atoms in a low spin (LS) diamagnetic configuration. Intraatomic exchange splitting is of similar energy to the crystal field of Co$^{3+}$ in an octahedral oxygen environment, and a transition from LS to high-spin (HS) can be induced by epitaxial tensile stress. We have grown ultrathin films of LCO ($\approx $2 nm) on top of SrTiO$_{3}$ (STO, $\approx $1.5 nm) and La$_{2/3}$Sr$_{1/3}$MnO$_{3}$ (LSMO, $\approx $22 nm). Magnetization and conductive AFM (C-AFM) experiments in the trilayer demonstrate that the ferromagnetic insulating behavior is kept in ultrathin LCO, with a T$_{\mathrm{C}}\approx $90 K, and M$\approx $0.8 $\mu_{\mathrm{B}}$/Co. The magnetization of LCO and LSMO is decoupled by the STO barrier, and so can be independently switched. C-AFM experiments show I-V curves characteristic of tunnel conduction between the ferromagnetic electrodes across the STO barrier. Moreover, the magnetization of both layers can be conveniently coupled/decoupled by changing the order of deposition of the films (either LCO/LSMO or LSMO/LCO). These results show that new approaches for the design of insulating ferromagnets are possible. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G6.00011: Structure, strain, and control of ground state property in LaTiO$_{3}$/LaAlO$_{3}$ superlattice Alex Taekyung Lee, Myung Joon Han We examined the ground state property of LaTiO$_{3}$/LaAlO$_{3}$ superlattice through density functional band calculations. Total energy calculations, including the structural distortions, $U$ dependence, and the exchange correlation functional dependence, clearly showed that the spin and orbital ground state can be controlled systematically by the epitaxial strain. In the wide range of strain, the ferromagnetic-spin and antiferro-orbital order are stabilized, which is notably different from the previously reported ground state in the titanate systems. By applying $+$2.8{\%} of tensile strains, we showed that the antiferromagnetic-spin and ferro-orbital ordered phase become stabilized. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G6.00012: Strain-Tunable Magnetocrystalline Anisotropy in Epitaxial Y3Fe5O12 Thin Films Hailong Wang, Chunhui Du, P. Chris Hammel, Fengyuan Yang Magnetocrystalline anisotropy plays an essential role in many applications and there is intense interest in understanding the role of magnetoelastic coupling in phonon-magnon interactions in thermal spintronics. It is important to understand magnetocrystalline anisotropy in the presence of lattice distortion induced by epitaxial strain and the underlying magnetization-lattice coupling. Y3Fe5O12 (YIG) has been widely used in microwave applications and spin pumping. Most YIG epitaxial film fabrication has employed Gd3Ga5O12 (GGG) substrates with nearly perfect lattice match. In order to probe the magnetocrystalline anisotropy and control magnetization by epitaxial strain in epitaxial YIG films, we grow YIG epitaxial thin films on (001)-oriented Y3Al5O12 (YAG) substrate with -3.0{\%} lattice mismatch. We demonstrate strain-tuning of magnetocrystalline anisotropy over a range of more than one thousand Gauss in epitaxial YIG films of excellent crystalline quality grown on YAG substrates. Ferromagnetic resonance (FMR) measurements reveal a linear dependence of both out-of-plane and in-plane uniaxial anisotropy on the strain-induced tetragonal distortion of Y3Fe5O12. Importantly, we find the spin mixing conductance determined from inverse spin Hall effect and FMR linewidth broadening remains large in Pt/YIG/YAG heterostructures, quite comparable to the value found in Pt/YIG grown on lattice-matched GGG substrates. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G6.00013: Strain's role at the 4-point phase boundary of La$_{0.4}$Sr$_{0.6}$MnO$_{3}$ T. Zac Ward, Anthony Wong, Hangwen Guo, Christianne Beekman, Zheng Gai Bulk La$_{0.4}$Sr$_{0.6}$MnO$_{3}$ shows a 4-point phase boundary where ferromagnetic metal, paramagnetic metal, canted antiferromagnetic metal, and A-type antiferromagnetic metal phases meet at 240K. The strong spin-charge-lattice coupling inherent in these materials make this a prime candidate for exploring the impact of interfacial strain effects on phase behavior. We use pulsed laser deposition to grow single crystal thin films of this composition on several different substrates to induce a range of epitaxial strains. We will present data showing a high level of tunability in resistive and magnetic properties and show the results as being directly tied to changes arising from shifts in the orbital occupancy. [Preview Abstract] |
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