Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R43: Magnetic Oxide InterfacesFocus
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Sponsoring Units: GMAG DMP DCOMP Chair: Daisuke Kan, Kyoto University Room: 390 |
Thursday, March 16, 2017 8:00AM - 8:12AM |
R43.00001: Investigation of the tunnel magnetoresistance in junctions with a strontium stannate barrier Matthias Althammer, Rohan Mishra, Albina J. Borisevich, Amit Vikam Singh, Sahar Keshavarz, Mehmet Kenan Yurtisigi, Patrick LeClair, Arunava Gupta We experimentally investigate the structural, magnetic and electrical transport properties of La$_{0.67}$Sr$_{0.33}$MnO$_3$ based magnetic tunnel junctions with a SrSnO$_3$ barrier $[1]$. Our results show that despite the high density of defects in the strontium stannate barrier the observed tunnel magnetoresistance is comparable to tunnel junctions with a better lattice matched SrTiO$_3$ barrier, reaching values of up to $350\;\%$ at $T=5\;\mathrm{K}$. Further analysis of the current-voltage characteristics of the junction and the bias voltage dependence of the observed tunnel magnetoresistance show a decrease of the TMR with increasing bias voltage. Our results suggest that by reducing the structural defects in the strontium stannate barrier, even larger TMR ratios might be possible in the future.\\ $[1]$ Althammer et al., arXiv, \textbf{1607.08393}, (2016) [Preview Abstract] |
Thursday, March 16, 2017 8:12AM - 8:24AM |
R43.00002: Tunneling anisotropic magnetoresistance in complex oxide tunnel junctions Benjam\'{\i}n Mart\'{\i}nez, Laura L\'opez-Mir, Regina Galceran, Lluis Balcells, Alberto Pomar, Zorica Konstantinovic, Felip Sandiumenge, Carlos Frontera The magnetotransport properties of La$_{\mathrm{2/3}}$Sr$_{\mathrm{1/3}}$MnO3(LSMO)/LaAlO$_{\mathrm{3}}$(LAO)/ Pt tunneling junctions have been analyzed as a function of temperature and magnetic field. The junctions exhibit magnetoresistance (MR) values of about 37{\%}, at H$=$ 90 kOe at low temperature. However, the temperature dependence of MR indicates a clear distinct origin than that of conventional colossal MR. In addition, tunneling anisotropic MR (TAMR) values around 4{\%} are found at low temperature and its angular dependence reflects the expected uniaxial anisotropy. The use of TAMR response could be an alternative of much easier technological implementation than conventional MTJs since only one magnetic electrode is required, thus opening the door to the implementation of more versatile devices. However, further studies are required in order to improve the strong temperature dependence at the present stage. [Preview Abstract] |
Thursday, March 16, 2017 8:24AM - 8:36AM |
R43.00003: Magnetic Properties of Ba$_{\mathbf{0.4}}$\textbf{Sr}$_{\mathbf{0.6}}$\textbf{TiO}$_{\mathbf{3}}$\textbf{/La}$_{\mathbf{0.7}}$\textbf{Sr}$_{\mathbf{0.3}}$\textbf{MnO}$_{\mathbf{3}}$\textbf{ heterostructures} Luis Martinez, Srinivasa Rao Singamaneni, John Prater, Jagdish Narayan Ba$_{1-x}$Sr$_{x}$TiO$_{3}$ is an excellent material for voltage-tunable dielectric applications. Ba$_{0}_{.}_{4}$Sr$_{0}_{.}_{6}$TiO$_{3}$ (BST)$^{1}$, which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the T$_{C}$ at 200K. The main focus here is to study what happens when BST (200nm) is placed in contact with ferromagnetic layer such as La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) (63nm), when BST/LSMO were deposited onto MgO/TiN buffered Si (100)$^{2}$. X-ray diffraction measurements showed that these films were of single phase and epitaxial in nature. The magnetic measurements showed that the Curie temperature (T$_{C})$ of LSMO remained unchanged at 350K when BST was in contact with LSMO layer. Interestingly, at 4K both the coercive field and the exchange bias of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at 200K. $^{1}$Singamaneni et al Appl. Phys. Lett., \textbf{108}, 142407 (2016); $^{2}$Appl. Phys. Rev. \textbf{3}, 031301~(2016). [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R43.00004: Quantum confinement in double perovskite multilayers: Sr$_{2}$FeMoO$_{6}$/La$_{2}$CoMnO$_{6}$ Subhasis Samanta, Birabar Nanda We have examined the interfacial electronic structure of multilayers grown along [001] out of half metallic ferrimagnet Sr$_{2}$FeMoO$_{6}$ (SFMO) and insulating ferromagnet La$_{2}$CoMnO$_{6}$ (LCMO) using the density functional theory calculations. The half-metallic nature arises due to the partial occupancy of xz, yz and x$^{2}$-y$^{2}$ states of SFMO in the spin minority channel. We find that LCMO provides a confinement potential along z the direction to the spin-polarized free electrons at the interface. The confinement potential ensures further quantization of the delocalized states, namely xz and yz of SFMO, lying on the Fermi level. The x$^{2}$-y$^{2}$ states remain unaffected and therefore, spin-polarized two dimensional electron gas (2DEG) is intrinsically formed. The formation of 2DEG is very distinct from that of the widely studied LAO/STO and LMO/SMO heterostructures. In these compounds, the 2DEG is formed via interfacial electron reconstruction to quench the polar catastrophe. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R43.00005: Enhanced Interfacial Ferromagnetism in (111)-Oriented LaNiO$_3$/CaMnO$_3$ Superlattices Charles Flint, Yuri Suzuki Interfacial ferromagnetism (i-FM) in complex oxides is a promising route for generating magnetic phenomena. An interesting example is FM in CaMnO$_3$ (CMO)-based superlattices (SLs), which is attributed to Mn-Mn double exchange (DE). In (LaNiO$_3$)$_N$/(CaMnO$_3$)$_M$ (LNO/CMO) SLs on (001)-oriented LaAlO$_3$, i-FM arises from Mn-Mn DE and Ni-Mn superexchange (SE). The relative contribution from these mechanisms can be tuned via cooperative distortions of the oxygen octahedra. For CMO, a G-type antiferromagnet, (001) planes are fully spin compensated, while (111) planes are fully uncompensated. Therefore, one may expect (111)-oriented SLs to have enhanced interfacial coupling, giving us insight into the interplay between the magnetic mechanisms in these SLs. We have fabricated LNO/CMO SLs on (111)-oriented LaAlO$_3$. We observe a significant enhancement in i-FM compared to (001)-oriented LNO/CMO SLs. Magnetometry measurements show that a (111)-oriented N=4, M=4 SL has more than a threefold enhancement in i-FM compared to the (001)-oriented N=4, M=4 SL with ~1.0 μB/int. Mn for (111) and ~0.3 μB/int. Mn for (001) SLs. These results are consistent with enhanced Ni-Mn SE arising from increased interfacial Ni-Mn bonding as a result of the (111) growth axis. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:36AM |
R43.00006: Resonant elastic x-ray scattering studies of magnetism in nickelate heterostructures Invited Speaker: Eva Benckiser Perovskite rare-earth nickelates exhibit an unusual period-four antiferromagnetic order. The realization of collinear and non-collinear spin structures and a different amplitude of magnetic moments on alternating nickel sublattices have been subjects of debate for decades. In my talk, I will present results of our resonant x-ray scattering studies on different nickelate-based heterostructures. In combination with density functional theory calculations and a local many-body model we showed that both, collinear and non-collinear magnetic states can be realized in thin NdNiO$_3$ layers if the interaction between neighboring magnetic sites is truncated along the [111] pseudocubic direction. Furthermore the relative size of nickel magnetic moments in the antiferromagnetic sublattices is determined by the crystallographic symmetry of the confining layers. In a second study we focused on the magnetic exchange interaction between rare-earth and transition-metal ions in epitaxial LaNiO$_3$-DyScO$_3$ superlattices and observed induced collinear magnetic order in interfacial Dy moments with the same periodicity as in LaNiO$_3$. The results give new, important insight to the relevant interactions stabilizing the magnetic order in nickelates and open up new perspectives for their selective manipulation. [Preview Abstract] |
Thursday, March 16, 2017 9:36AM - 9:48AM |
R43.00007: Numerical study of resonant inelastic x-ray scattering for transition-metal complexes and oxides Chunjing Jia, Brian Moritz, Yao Wang, Thomas Devereaux Resonant inelastic x-ray scattering (RIXS) has become an important technique for understanding electronic transitions in transition-metal complexes and low-energy excitations in transition-metal oxides. A theoretical understanding of RIXS for such correlated systems has remained a challenge, especially for understanding momentum dependence and photon-polarization. Here we present exact diagonalization results for RIXS spectra at the Co K pre-edge for Co complexes to understand valence tautomerism. A more general method for calculating RIXS on transition metal oxides, which includes multiplet and charge-transfer effects, will also be discussed. [Preview Abstract] |
Thursday, March 16, 2017 9:48AM - 10:00AM |
R43.00008: Spin State Control using Oxide Interfaces in LaCoO$_{\mathbf{3}}$\textbf{-based Heterostructures} Sangjae Lee, Ankit Disa, Frederick Walker, Charles Ahn The flexibility of the spin degree of freedom of the Co 3d orbitals in LaCoO$_{3}$ suggests that they can be changed through careful design of oxide heterostructures. Interfacial coupling and dimensional confinement can be used to control the magnetic exchange, crystal fields, and Hund's coupling, through orbital and charge reconstructions. These parameters control the balance between multiple spin configurations, thereby modifying the magnetic ordering of LaCoO$_{3}$. We study (LaCoO$_{3})_{m}$/(LaTiO$_{3})_{2}$ heterostructures grown by molecular beam epitaxy, which allow interfacial charge transfer from Ti to Co, in addition to structural and dimensional constraints. The electronic polarization at the interface and consequent structural distortions suppress the ferromagnetism in the LaCoO$_{3}$ layers. This effect extends well beyond the interface, with ferromagnetic order absent up to LaCoO$_{3}$ layer thickness of m$=$10. We compare the properties of the LaCoO$_{3}$/LaTiO$_{3}$ heterostructures with LaCoO$_{3}$/SrTiO$_{3}$, to untangle how charge transfer and structural modifications control the spin and magnetic configuration in cobaltates. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R43.00009: Magnetism and electronic order in SmTiO$_{\mathrm{3}}$ quantum well heterostructures Ryan Need, Patrick Marshall, Brandon Isaac, Eugen Weschke, Andreas Suter, Michael Graf, Susanne Stemmer, Stephen Wilson Complex oxide heterostructures that possess high density interfacial electron gases due to charge discontinuities between neighboring layers provide a unique platform with which to study correlated electron physics. In heterostructures containing band insulator SrTiO$_{\mathrm{3}}$ and Mott insulating rare earth titanate layers, it has been shown that tuning relative layer thicknesses can in turn tune both the electronic and magnetic properties found in each layer type, leading to exotic metal-insulator transitions and electronic symmetry breaking in the interleaving quantum wells. Here we use a combination of resonant x-ray reflectometry (RXR), polarized neutron reflectometry (PNR), and muon spin rotation (muSR) to probe the electronic and magnetic properties of SmTiO$_{\mathrm{3}}$ thin films and SrTiO$_{\mathrm{3}}$-SmTiO$_{\mathrm{3}}$ heterostructures. RXR measurements demonstrate the effect of tuning both SrTiO$_{\mathrm{3}}$ and SmTiO$_{\mathrm{3}}$ layer thicknesses on the electronic structure, and our combined PNR and muSR results resolve the freezing of interface-induced free electrons within the SrTiO$_{\mathrm{3}}$ quantum wells below a critical temperature. The correlations between our scattering results and previously reported anomalous transport in SrTiO$_{\mathrm{3}}$-SmTiO$_{\mathrm{3}}$ heterostructures will be discussed. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R43.00010: Emergent magnetism of quasi-two-dimensional frustrated lattices by geometric design Xiaoran Liu, B Kirby, B Pal, Y Cao, M Kareev, D Sarma, J Freeland, P Shafer, E Arenholz, J Chakhalian When antiferromagnetic exchange interactions cannot be satisfied simultaneously on triangle-related lattices, the systems become geometrically frustrated with magnetically disordered phases significantly different from simple paramagnets. From theory, spin liquid belongs to one of these exotic states, in which a macroscopic degeneracy of the ground state coexist, giving rise to remarkable collective phenomena. So far, very few candidates have been achieved experimentally due to the challenges in fabricating the peculiar lattices with networks of triangles. Here, we report the discovery of emergent magnetic states on artificial heterostructures composed of ultrathin (111)-oriented CoCr$_{\mathrm{2}}$O$_{\mathrm{4}}$ sandwiched by nonmagnetic Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ spacer. We reveal the degree of frustration is remarkably enhanced at the two-dimensional limit, where the slab of CoCr$_{\mathrm{2}}$O$_{\mathrm{4}}$ contains four alternating layers of triangle and kagome planes. The system sustains a spin-disordered state down to 2 K without any magnetic phase transition, indicating possible realization of a spin liquid phase. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R43.00011: Interfacial magnetism in manganite-based synthetic multiferroics S.G.E. te Velthuis, Q. Wang, Y. Liu, H. Ambaye, V. Lauter, T.R. Charlton, M.R. Fitzsimmons, M. Cabero, J. Santamaria Ferromagnetic/ferroelectrics heterostructures, i.e. synthetic multiferroics, provide a pathway for studying the competition between these incompatible orders and the interfacial magnetoelectric coupling, which may be utilized for energy-efficient spintronics. We present polarized neutron reflectometry (PNR) results on La$_{0.7}$Sr$_{0.7}$MnO$_{3}$ (LSMO) and ferroelectric BaTiO$_{3}$ (BTO) heterostructures. We find that the magnetization and anisotropy of the LSMO layer near the interfaces is modified with respect to the central part of the layer. While a pinned magnetization is observed at the STO interface, instead a weaker anisotropy is found at the BTO interface. These results are discussed in relationship to the tunnel magnetoresistance measurements of this system, that indicate oxygen vacancies can be induced within BTO and manipulated with electric fields. Due to charge transfer, oxygen vacancies at the interface can result in modification of the interfacial magnetism of the LSMO. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R43.00012: Spin Hall Effect Driven Non-Local Spin Diffusion at Oxide Heterointerfaces. MiJin Jin, Seon Young Moon, Jungmin Park, Vijayakumar Modepalli, Junhyeon Jo, Shin-Ik Kim, Hyun Cheol Koo, Byoung-Chul Min, Hyun-Woo Lee, Seung-Hyub Baek, Jung-Woo Yoo The conductive interface at LaAlO3/SrTiO3 (LAO/STO) can be designed to exhibit high mobility with tunable carrier concentration and exhibits various unique electronic behaviors. This interface could be also interesting playground for `'spin-orbitronics'' as the structure itself strongly couple the spin and orbital degree of freedom through the Rashba spin-orbit interaction. We report the non-local spin diffusion at LAO/STO interface induced by the spin Hall effect. The Hall-bar (H-bar) like geometry was employed to generate a transverse spin polarized current, which in turn can be detected by the inverse spin Hall effect. Our results clearly demonstrated the non-local spin diffusion as well as effective spin charge conversion at this oxide heterointerface. The analysis on the non-local spin voltage displays that both D''yakonov-Perel'' and Elliott-Yafet mechanisms involve in the spin relaxation. Our results show that the oxide heterointerface is highly efficient in spin-charge conversion with exceptionally strong spin Hall coefficient $\gamma $ \textasciitilde 0.24 and could be an outstanding platform for the study of coupled charge and spin transport phenomena and their electronic applications. [Preview Abstract] |
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