Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S37: Multipolar and Novel Magnetic Orders in Complex OxidesFocus Live
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Sponsoring Units: GMAG DMP DCOMP Chair: Pat Woodward, Ohio State University |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S37.00001: Multipolar orders in d-orbital systems Invited Speaker: Arun Paramekanti Traditionally, magnetism in solids deals with ordering patterns of the electron magnetic dipole moment, as probed, for instance, via neutron diffraction. However, in quantum materials can also exhibit more complex forms of symmetry breaking, involving higher-order magnetic or electric multipoles. In this talk, I will discuss our recent theoretical proposal for Ising octupolar order in d-orbital systems, which explains a wide range of experiments in certain 5d transition metal oxides with spin-orbit coupling. Such multipolar symmetry broken states might serve as potential platforms for information storage. I will also highlight new experiments on realizing 2DEGs with j=3/2 fermions, which our theory suggests as candidates for multipolar stripe ordering. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S37.00002: Multipolar magnetism in d-orbital systems: Crystal field levels, octupolar order, and orbital loop currents Sreekar Voleti, Dalini D Maharaj, Bruce Gaulin, Graeme Luke, Arun Paramekanti Quantum magnets with spin J=2, which arise in spin-orbit coupled Mott insulators, can potentially display multipolar orders. Motivated by gaining a better microscopic understanding of the local physics of such d-orbital quantum magnets, we carry out an exact diagonalization study of an octahedral crystal field Hamiltonian for two electrons, incorporating spin-orbit coupling and interactions. While the rotationally invariant Kanamori interaction in the t2g sector leads to a five-fold degenerate J=2 manifold, we propose two mechanisms which cause a degeneracy breaking of the J=2 levels. This can lead to a low-lying non-Kramers doublet carrying quadrupolar and octupolar moments, where spontaneous time-reversal symmetry breaking due to ferro-octupolar ordering within the doublet leads to electronic orbital loop currents. The resulting internal magnetic fields can potentially explain the small fields inferred from muon-spin relaxation (μSR) experiments on cubic 5d2 Osmate double perovskites. Our work highlights the intimate connection between the physics of heavy transition metal oxides and that of f-electron based heavy fermion compounds. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S37.00003: 4d/5d Row Transition Metal Oxide d-Orbital Systematics by X-Ray Absorption Near Edge Spectra (XANES) Eric Kurywczak, Mehmet Alper Sahiner, Mark Clyde Croft XANES L2 and L3-edge X-Ray Absorption Near Edge Spectra (XANES) for 4d and 5d row transition metals (TM) oxides are assumed to directly reflect unoccupied d-orbitals influenced by the local symmetry of the metal ion.1 XANES L2 and L3-edge data analysis through non-linear curve fitting allows for a unique, efficient look at the structural eccentricities of transition metal oxides. In this way it is possible to determine the oxidation state of a material as well as its site symmetry. We have used non-linear least-squares fitting across the near-edge region of various 4d row and 5d row TM oxides in order to investigate the systematics of their d-orbital occupancies and the XANES white line features for t2g and eg symmetry orbitals. The statistics show promising trends to be expected in 4d and 5d row level transition metal oxides. The systematics obtained by these results provide crucial information for the synthesis of the new materials with specific electronic structures and crystal symmetries. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S37.00004: Diamagnetic d10 and d0 cations direct magnetic interactions in double perovskites Otto Mustonen, Charlotte Pughe, Helen Walker, Heather Mutch, Gavin Stenning, Fiona Coomer, Edmund Cussen The main magnetic interaction in oxides is superexchange mediated by oxygen anions. Recently, it has been shown that diamagnetic d10 and d0 cations can play a role in extended superexchange interactions due to differences in orbital hybridization. Here we formulate simple rules for this d10/d0 effect in A2B'B''O6 double perovskite oxides. We have investigated magnetic interactions in cubic Mn2+ double perovskites Ba2MnTeO6 (d10 Te6+) and Ba2MnWO6 (d0 W6+). Our analysis reveals d10 cations on the B'' site promote strong J1 interactions, while d0 cations promote J2 interactions. This effect is general to 3d transition metal double perovskites. The d10/d0 effect can be used to tune magnetic interactions and ground states as we have previously shown for Sr2CuTe1-xWxO6, where the ground state can be tuned from magnetic order to a random singlet state. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S37.00005: Structural and magnetic properties in a planar antiferromagnet Xiang Chen, Yu He, Shan Wu, Yu Song, Dongsheng Yuan, Edith Bourret-Courchesne, Jacob Ruff, Zahir Islam, Alex Frano, Robert J Birgeneau A monoclinic compound barium iridium oxide was proposed to host exotic magnetic ground states. By using a combination of thermodynamic, magnetometry and resonant x-ray scattering techniques, we report the structural and magnetic properties of this momoclinic compound. The magnetization data indicates a pronounced antiferromagnetic transition at 25K, a weaker anomaly at 142K, and strong magnetic anisotropy at all temperatures. Resonant elastic x-ray scattering experiments reveal a second order structural phase transition at Ts~142K and a magnetic transition at Tn~25K. Both structural and magnetic superlattice peaks are observed. Magneto-elastic coupling might facilitate the symmetry lowering at Ts, which induces the magnetic anomaly in the magnetization data. Furthermore, our scaling analysis suggests the mean-field like structure transition at Ts. The magnetic ground state below Tn is discussed based on the measured magnetic superlattice peak intensity. Our study presents valuable information for understanding the structural and magnetic properties in this new barium iridium oxides. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S37.00006: Competing magnetic interactions in Sr3(Ru1-xMnx)2O7 Roshan Nepal, Lingyi Xing, Rongying Jin Correlated transition-metal oxides continue to attract widespread interest due to the abundance of exciting phenomena arising from the strong interactions between several degrees of freedom. Among them, the bilayered ruthenate Sr3Ru2O7 is known for its dramatic response to chemical substitution among other external stimuli. The remarkable evolution of the magnetic ground state due to a partial substitution of Ru by Mn in Sr3(Ru1-xMnx)2O7 has been characterized through our experimental investigations. Due to the inherent ferromagnetic (FM) and antiferromagnetic (AFM) interactions in x = 0, introducing Mn results in initially an E-type AFM ordering (x < 0.2) then a spin glass (SG) behavior for 0.20 < x < 0.66 before forming a canted AFM ordering in x = 1 (Sr3Mn2O7). The wide range of the SG state indicates strong competition of FM and AFM interactions. A complete phase diagram of Sr3(Ru1-xMnx)2O7 will be presented. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S37.00007: Large spin-driven dielectric response and magnetoelectric coupling in the buckled honeycomb Fe4Nb2O9 Huibo Cao, LEI DING, Minseong Lee, Eun Sang Choi, Yan Wu, Ryan P Sinclair, Bryan C Chakoumakos, Haidong Zhou A significant spin-driven dielectric anomaly near the magnetic ordering temperature has been observed in single crystal Fe4Nb2O9. By combining neutron and x-ray single crystal diffraction, we unambiguously determined its magnetic symmetry and studied the structural phase transition. The temperature-dependent static dielectric constant is strongly anisotropic, rendering two dielectric anomalies along the a axis in the hexagonal lattice with the first one coupled to the magnetic ordering around TN = 97 K and the second one accompanying with a first-order structural transition around TS = 70 K. Below TN , we found that the anomalous dielectric constant is practically proportional to the square of the magnetic moment from neutron diffraction data, indicating that the exchange striction is likely responsible for the strong spin-lattice coupling. |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S37.00008: Interplay between local and itinerant magnetism in transition metal oxides: the role of anion magnetism Swamynadhan M J, Donghan Shin, Andrew O'Hara, Saurabh Ghosh, Sokrates T Pantelides Transition-metal oxides (TMOs) have been studied widely for their fascinating properties. Recently, neutron diffraction experiments and density-functional-theory (DFT) calculations found sizable magnetic moments on the oxygen anions in ferromagnetic SrRuO3. In general, using appropriate functionals, DFT captures the magnetic properties of many TMOs. Here, we report comprehensive DFT calculations in a wide range of 3d-, 4d-, and 5d-TMOs and a few sulfides, aiming to elucidate the microscopic origin of anionic magnetization. We examine the local spin density of states, radial dependence of magnetization, and strain sensitivity. Cation-anion bond lengths play a major role in controlling the degree of anionic magnetization. However, we find a complex spin-density distribution in both coordinate and energy space, whereby the simple picture of TM d-orbitals overlapping the anions is not sufficient to account for the magnitude of anion magnetic moments. Anion magnetic moments range from zero (Heisenberg ferromagnets) to values that are comparable to cation magnetic moments (itinerant ferromagnets). |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S37.00009: Neutron scattering study of Na2Co2TeO6 single crystals Weiliang Yao, Yuan Li, Kazuki Iida, Kazuya Kamazawa Spin-orbital entangled Mott insulators have been focused to search for the novel Kitaev physics in real magnets. Recently d7 high-spin compounds have become a new platform to realize the spin-anisotropic exchange interaction after many years of studies on the d5 cases [1,2]. With d7 Co2+ ion, Na2Co2TeO6 is regarded as one of the promising candidate materials [1] and it was experimentally found to exhibit some resemblances[3] to the famous α-RuCl3. To further understand the magnetic interactions in this compound, we have performed inelastic neutron scattering experiments on Na2Co2TeO6 single crystals. In this talk, we will present its magnetic excitation spectrum and make the comparison to other honeycomb magnets, in order to assess the prominence of Kitaev physics in this system. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S37.00010: Probing quantum spin liquids in equilibrium using the inverse spin Hall effect Joshua Aftergood, So Takei We propose a strongly spin-orbit coupled metal to quantum magnet bilayer as a probe of quantum magnets lacking long range magnetic order, e.g., quantum spin liquids (QSLs), via examination of the voltage noise spectrum in the metal layer. The bilayer is held in equilibrium, and spin fluctuations arising across the interface are converted into voltage fluctuations in the metal via the inverse spin Hall effect. We show the theoretical workings of the system, and predict the frequency characteristics of the enhancement to the ac electrical resistance measured in the metal layer for three QSL models. We apply our model to the Heisenberg spin-1/2 kagome lattice model, a QSL consisting of fermionic spinons coupled to a U(1) gauge field, and the Kitaev model in the gapless QSL phase. In each case we extract characteristic features of a given QSL model, and therefore show that spectral analysis of the ac resistance across the metal layer in a single interface, equilibrium bilayer can test the relevance of a QSL model to a given candidate material. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S37.00011: Competing energetic states in γ-Fe2WO6 with strong spin-charge-lattice coupling Milos Sretenovic, Satoshi Okamoto, Gordon Peiker, Xudong Tang, Heda Zhang, CQ Xu, Thomas W Heitmann, Clarina Dela Cruz, Xianglin Ke We report magnetic and electronic properties of γ-Fe2WO6 via neutron powder diffraction measurements and first-principles density function theory calculations. We reveal a magnetic ground state which is distinct from an earlier report [1], despite the fact that both materials studied have the same space group but with slightly different atomic positions. Interestingly, both spin structures are well captured by first-principles calculations. Furthermore, we show that the spin structures of this system are correlated with electronic properties, with one being insulating and the other being metallic. These features suggest that γ-Fe2WO6 exhibits competing energetic states in which spin, charge, and lattice degrees of freedom are strongly coupled to each other. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S37.00012: Structure of the magnetic order induced by Ti-doping in Sr2RuO4 Bastian Zinkl, Manfred W Sigrist Replacing less than one percent of Ru atoms by non-magnetic Ti4+ is sufficient to induce incommensurate spin density wave order in Sr2RuO4. The ordering wave vector Q ∼ (2π/3, 2π/3) coincides with the nesting vector of two out of three Fermi surface sheets. We consider a microscopic model for these two bands and explore the formation of magnetic order through doping with non-magnetic impurities. For this purpose we develop a spatially resolved mean field theory for the microscopic model including spin-orbit coupling and a phenomenological Ginzburg-Landau formulation. The different approaches, which are connected by an effective field theory derived from the microscopic model, deliver consistent results and allow us to examine the inhomogeneous magnetic order. Extending the field theory into a gauge field theory in both charge and spin channels reveals several more features of the system due to spin-orbit coupling, such as impurity induced spin currents and the connection between charge currents and spin polarization. Our findings allow a more detailed analysis of the experimental data for Sr2Ru1-xTixO4. In particular, we find that the available measurements are consistent with our theoretical predictions. |
Thursday, March 18, 2021 2:18PM - 2:30PM Live |
S37.00013: Competition of three-dimensional magnetic phases in Ca$_2$Ru$_{1-x}$Fe$_x$O$_4$: A structural perspective Songxue Chi, Feng Ye, Gang Cao, Huibo Cao, Jaime Fernandez-Baca The crystalline and magnetic structures of Ca$_2$Ru$_{1-x}$Fe$_x$O$_4$ have been studied using neutron and X-ray diffraction. The Fe-doping reduces the Ru-O bond length in both apical and planar directions. The smaller Ru(Fe)O$_6$ octahedron leads to its reduced distortion. The $Pbca$ space group is maintained in all the Fe-dopings, so is the octahedral flattening. Two competing antiferromagnetic orders, $A$- and $B$-centered phases have been observed. The Fe-doping-relaxed crystal structure prefers the latter to the former. The absence of the two-dimensional antiferromagnetic critical fluctuations above the magnetic transition temperature and the three-dimensional magnetic correlation below the transition, together with the anomalous lattice response, point to an important role of orbital degree of freedom in driving the magnetic phase competition. |
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