Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S40: Emergent Phases in Magnetic OxidesFocus
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Sponsoring Units: GMAG DMP Chair: Nandini Trivedi, Ohio State University Room: BCEC 208 |
Thursday, March 7, 2019 11:15AM - 11:51AM |
S40.00001: Emergent electronic phases in Ruddlesden-Popper chromium oxide perovskites Invited Speaker: Riccardo Comin Chromium-based compounds realize a multitude of electronic and magnetic phases: half-metals (CrO2), ferromagnetic insulators (CrI3, YCrO3), antiferromagnetic insulators (Cr2Se3, CrSe2, Cr2O3 and LaCrO3), or antiferromagnetic metals (Cr and SrCrO3). These compounds, whose magnetic transitions are often near room temperature, represent a far less charted platform for emergent quantum matter compared to their other 3d transition metal siblings. |
Thursday, March 7, 2019 11:51AM - 12:03PM |
S40.00002: Rh-based Double Perovskites with Unusual Properties: A computer prediction Tanusri Saha-Dasgupta, Anita Halder, Prabuddha Sanyal Using a combination of computational tools involving genetic algorithm, denisty functional theory and finite temperature Monte Carlo simulation, we make prediction on yet-to-be synthesized Rh-based double perovskites with novel properties. |
Thursday, March 7, 2019 12:03PM - 12:15PM |
S40.00003: Transition between two metallic ferroelectric orders in multiferroic Ca3Ru2O7, induced by magnetism-mediated orbital re-polarization Zheting Jin, Wei Ku For the past decades, the low-temperature phase of Ca3Ru2O7 below the 48K first-order phase transition remains a puzzle with controversial suggestions involving metallic ferroelectric, orbital or magnetic ordering. |
Thursday, March 7, 2019 12:15PM - 12:27PM |
S40.00004: Electronic correlations in early transition metal oxides with oxygen vacancies Jaime Souto Casares, Nicola Spaldin, Claude Ederer Oxygen vacancies are known to affect profoundly the properties of the host system, coupling to the already coupled degrees of freedom. Electronically, in early transition metal oxides, the presence of oxygen vacancies locates electronic states in the gap between the transition metal t2g-band and the oxygen p-band, with occasional occurrences of crossings with the t2g-band. The closeness and influence of the vacancy band on the correlated electronic bands calls for a beyond-DFT analysis. Constructing an extended t2g correlated subspace where the oxygen vacancy state is explicitly consider, we have performed dynamical mean-field theory (DMFT) and constrained random phase approximation (cRPA) calculations for three different lanthanum transition metal oxides with different t2g-occupations (LaBO3, with B={Ti(d1), V(d2), Cr(d3)}) in order to investigate what is the effect of the vacancy on the Mott insulating phase, and to monitor how the ab-initio effective Coulomb interaction parameters change. |
Thursday, March 7, 2019 12:27PM - 12:39PM |
S40.00005: An ab-initio DFT+DMFT study of the effect of oxygen vacancies on structural, electronic and magnetic properties of rare-earth nickelate perovskites (RNiO3) Uthpala Herath, Hyowon Park, Aldo H Romero The electronic correlations in materials are responsible for a variety of fascinating phenomena including magnetism, superconductivity, colossal magnetoresistance and metal-insulator transitions. As shown in previous studies, the ability to manipulate the oxygen vacancies within these strongly correlated materials gives rise to new degrees of freedom in tuning their properties. We employ ab-initio density functional theory (DFT) coupled to dynamical mean field theory (DMFT) calculations to systematically study the influence of oxygen vacancies on structural, electronic and magnetic properties of strongly correlated rare-earth nickelates, RNiO3 (R-rare earth element). The DFT Kohn-Sham orbitals are projected onto maximally localized Wannier Functions within a hybridization window to provide the correlated subspace for the DMFT problem which is solved using a continuous time quantum Monte-Carlo (CTQMC) algorithm. Based on our calculated results we elucidate the role of oxygen vacancies on the material properties also focusing their effects on individual orbitals, which thus far has not been studied extensively in the case of strongly correlated rare earth nickelate perovskites. |
Thursday, March 7, 2019 12:39PM - 12:51PM |
S40.00006: The Electronic Structure and Properties of Negative Charge Transfer Compounds Robert Green, George Albert Sawatzky In high oxidation state oxides like the trivalent nickel oxides, tetravalent cobalt and iron oxides as well as the parent superconductors BaBiO3 and SrBiO3, the cation electron affinity for the formal valence taking oxygen to be 2- can result be larger than the oxygen ionization potential. This leads to a so-called negative charge transfer energy, where the cations are more accurately described with reduced valences and the oxygen states are self-doped with holes. As a consequence, one can have very different electronic structures and x-ray spectra than expected from the formal oxidation state picture. We demonstrate that with this in mind we can very well explain many of the properties and phases of the trivalent nickelates and tetravlent ferrates. Utilizing the negative charge transfer approach in cluster exact diagonalization calculations resolves a 25 year old puzzle concerning core level spectra of nickelates, and reveals interesting orbital polarization phenomena in strained nickelate and ferrate films. |
Thursday, March 7, 2019 12:51PM - 1:03PM |
S40.00007: Evolution of Antiferromagnetism with Hole Doping in HgBa2Ca2Cu3O8: A Parameter Free Perspective Christopher Lane, Yubo Zhang, Matthew Matzelle, Johannes Nokelainen, James Furness, Robert Markiewicz, Bernardo Barbiellini, Jianwei Sun, Arun Bansil Since the discovery of the cuprates 33 years ago, connecting their physical properties to their electronic structure has proven extremely challenging to capture within a uniform theoretical picture. Here, by utilizing the recently constructed SCAN metaGGA, we show how the charge, spin and lattice degrees of freedom of HgBa2Ca2Cu3O8+δ evolve with oxygen hole doping. Both the layer and doping dependence of our theoretically predicted antiferromagnetic order are in good agreement with NMR observations. In particular, a local maximum in the number of holes in the CuO2 plane is found in agreement with near optimal δ=0.16 doping for high-Tc superconductivity. Additionally, we find the doped interstitial oxygens play a consequential role at the Fermi level throughout the phase diagram, indicating the importance of inter-layer coupling between the CuO2 planes and the charge reservoir layer. |
Thursday, March 7, 2019 1:03PM - 1:15PM |
S40.00008: Antiferromagnetism in a rocksalt high entropy oxide Junjie Zhang, Jiaqiang Yan, Stuart Calder, Qiang Zheng, Erich T. Von Geis, Douglas L Abernathy, Yang Ren, Saul H. Lapidus, Katharine L. Page, Hong Zheng, John William Freeland, John D Budai, Raphael Hermann High entropy oxides have attracted much attention because they not only significantly broaden the phases beyond the conventional phase diagram of doping, but also have the potential to exhibit multifunctional physical properties and emergent phenomena including superconductivity and quantum criticality [1-3]. The existence of extreme chemical disorder in these materials is expected to suppress the long range magnetic order. Here, by combining magnetometry, synchrotron x-ray and neutron powder diffraction, we report for the first time that a rocksalt high entroy oxide exhibits long range antiferromagnetic order at ~120 K with q=(½, ½, ½). Inelastic neutron scattering reveals strong magnetic excitations at 100 K that survive up to room temperature. The shear modulus obtained from resonant ultrasound spectroscopy shows an anomaly around the magnetic transition, and surprisingly it hardens with decreasing of temperature without saturation down to 3 K. References: [1] Rost, C. M. et al. Nat. Commun. 6, 8485 (2015). [2] Gao, M. C. et al. J. Mater. Res., 1-18 (2018). [3] Sales, B. C. et al. npj Quantum Mater. 2, 33 (2017). |
Thursday, March 7, 2019 1:15PM - 1:27PM |
S40.00009: The effect of the Co-O covalency on the spin-state ordering in LaCoO3: A DFT+DMFT study Hyowon Park, Ravindra R Nanguneri We investigated the effect of the Co-O covalency on the spin-state transition in LaCoO3 using the charge-self-consistent density functional theory plus dynamical mean field theory (DFT+DMFT) method imlemented using the maximally localized Wannier functions as basis sets. The strong covalent bonding between Co and O produces the occupancy of the Co d orbital as d7 with one hole in the O ion when computed using DFT+DMFT with the fully localized form of the double counting potential. The effect of the Co-O covalency is studied by changing the double counting potential within DFT+DMFT for both homogeneous and the mixed high/low spin states. The total energy calculation of DFT+DMFT shows that the low-spin state is the lowest in energy for the d occupancy close to 7 while the spin-state ordering (high and low spins) between two Co ions occurs when the d occupancy is below 6.7 as the Co-O covalency is reduced. The valence histogram in DFT+DMFT shows that the charge ordering also occurs for the spin-state ordered LaCoO3 as the higher spin state Co ion has a higher d6 configuration than the low-spin state Co ion does. Both the charge and the energy differences between the homogeneous and the spin-state ordered phases are smaller in DFT+DMFT compared to DFT+U results. |
Thursday, March 7, 2019 1:27PM - 1:39PM |
S40.00010: Spontaneous non-stoichiometry and ordering of metal vacancies in degenerate transparent conductive oxides Oleksandr Malyi, Michael T. Yeung, Kenneth Poeppelmeier, Clas Persson, Alex Zunger The existence of non-stoichiometry in oxides is often thought to be a growth effect rather than a specific electronic instability. We show via DFT calculations that the presence of electrons in the conduction band of insulators can destabilize materials with respect to the spontaneous formation of cation vacancy acceptors. These tendencies result ultimately in the formation of ordered vacancy compounds (OVCs). For Ca-Al-O and Ba-Nb-O, we find that OVCs with different stoichiometries l:m:n are stable under different ranges of elemental chemical potentials, controllable during synthesis. Since each l:m:n OVC depletes the conduction band of electrons by a different amount, the formation of OVCs can be used to reduce plasma absorption, modify interband absorption, and enhance materials stability. This clarifies how non-stoichiometry often seen in oxides is an electronic effect – a high Fermi energy induces the formation of electron-killer acceptors such as cation vacancies. This also provides insights into the stability of the transparent conductive states while pointing out that controllable formation of non-stoichiometric degenerate insulators can be used to design next-generation transparent conductive oxides. |
Thursday, March 7, 2019 1:39PM - 1:51PM |
S40.00011: Magnetic percolation transition in diluted hexaferrites Cameron Lerch, Thomas Vojta The hexagonal ferrites BaFe12O19, SrFe12O19 and PbFe12O19 are ferrimagnets with Neel temperatures of approximately 720K that also show interesting ferroelectric properties. By randomly substituting Ga ions for the Fe ions, the Neel temperature can be suppressed to zero. Recent experiments [1] have found the phase boundary to vary as TN ∼ (1 - x/xc)2/3 over a wide x range, with xc very close to the percolation threshold of the iron spins. The shape of the phase boundary in the neighborhood of xc does not agree with current theoretical predictions for a classical percolation transition. We investigate the shape of the low-temperature phase boundary close to the percolation threshold using large-scale Monte Carlo simulations of a three-dimensional site-diluted Heisenberg model. |
Thursday, March 7, 2019 1:51PM - 2:03PM |
S40.00012: Variations in the Magneto-optical Properties of CuAl1-xFexO2 with Fe Concentration Mina Aziziha, James Patrick Lewis, Seth A Byard, Mohindar S Seehra, Matthew Bruce Johnson CuAlO2 is among several ternary delafossites in which the electronic bandgap (2.68 eV) is less than the optical bandgap (3.5 eV). Because alloying is expected to allow band engineering in delafossites, we are investigating magneto-optical properties of CuAl1-xFexO2 for x = 0 to1. The samples were prepared by solid-state reaction in air. X-ray diffraction of the powder samples shows an expansion of the rhombohedral unit cell with increasing x, in accordance with Vegard’s Law. X-ray photoelectron spectroscopy, and SEM-based energy dispersive (x-ray) spectroscopy were also used to confirm the Fe concentrations. Analysis of the magnetization (M) vs. temperature data (T = 2 to 300 K) and magnetic field (up to H = 90 kOe) verifies Fe3+ as the electronic state of Fe and Fe3+-Fe3+ exchange coupling signifies anti-ferromagnetism for CuAl1-xFexO2 for x = 0 to 0.1. The high-resolution M vs. H hysteresis loop measurements done at 300 K and 10 K shows some hysteresis, particularly for the x= 0.1 sample. However, it is concluded that this hysteresis is due to hematite impurity which is not detectable in the XRD analysis of the samples. In this talk, we will specifically report on magnetic measurements of CuAl1-xFexO2 for x > 0.1 and optical absorption studies in the CuAl1-xFexO2 samples. |
Thursday, March 7, 2019 2:03PM - 2:15PM |
S40.00013: Anti-doping in Insulators and Semiconductors Qihang Liu, Gustavo Dalpian, Alex Zunger Ordinary doping by electrons (holes) generally means that the Fermi level shifts towards the conduction band (valence band) and that the conductivity of free electrons (holes) increases. Recently, however, some peculiar doping characteristics were sporadically recorded in different materials without noting the mechanism: electron doping was observed to increase the band gap and thus lead to a decrease in conductivity. This behavior we dub as “anti-doping” was seen in rare-earth nickel oxides SmNiO3, cobalt oxides SrCoO2.5, Li-ion battery materials and even MgO with metal vacancies. Given the apparent generality of this phenomenon and that it may offer an unconventional way of controlling conductivity, we demystify the physical origin of anti-doping as well as its inverse problem – the “design principles” that would enable intelligent search of materials. We find that electron anti-doping is expected in materials having pre-existing trapped holes and is caused by annihilation of such “hole polarons” via doping. |
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