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 Y37: Bulk Complex Oxides: ExperimentsFocus Live
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Sponsoring Units: GMAG DMP DCOMP Chair: Rebecca Dally, National Institute of Standards and Technology |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y37.00001: Non-Kramers doublet ground state of the triangular-lattice spin-liquid candidate TbInO3 Mai Ye, Xianghan Xu, Xiangyue Wang, Jaewook Kim, Sang-Wook Cheong, Girsh Blumberg Ferroelectric insulator TbInO3 has been proposed to be a 2D spin-liquid candidate. This material has a Weiss temperature of -17K, but no magnetic ordering occurs down to 0.1K [Nat. Phys. 15, 262 (2019)]. It remains unclear whether the magnetic lattice has honeycomb or triangular symmetry at low temperature. We study the ground state properties of this system by probing its crystal-field (CF) excitations using inelastic light scattering. The experimentally established CF level scheme provides a satisfactory description for the low-temperature specific heat and entropy data. In particular, we demonstrate that the Tb ions have a non-Kramers doublet ground state, and these doublets from a triangular magnetic lattice. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y37.00002: Partial melting of the charge order in the mixed-valent homometallic ludwigite Co22+Co3+BO5 Carlos William Galdino, Cynthia P. C. Medrano, Daniele C Freitas, Gustavo Azevedo, Carlos B. Pinheiro, Mucio A. Continentino, Eduardo Granado Co22+Co3+BO5 is investigated from 6 to 800 K by single crystal X-ray diffraction (XRD), Raman spectroscopy, neutron diffraction (NPD) and Co K-edge X-ray absorption spectroscopy (XANES and EXAFS), where the latter is analyzed by reverse Monte Carlo methods with a genetic algorithm [1]. XANES data demonstrate the coexistence of Co2+ and Co3+ ions over the investigated temperature interval. XRD, NPD and EXAFS data show that all four Co1-Co4 sites present nearly rigid CoO6 octahedra up to ~400 K, with the smallest Co4 site hosting the Co3+ ions. Above 400 K, a substantial lattice disorder is perceived, accompanied by an increment (reduction) of the mean Co4-O (Co2-O) distances up to ~500 K that indicates a redistribution of the Co charges inside the Co4-Co2-Co4 ladders in this temperature interval [2]. The phonon Raman spectra are sensitive to the partial melting of charge order at ~400-500 K, also showing anomalies related to short-range magnetic correlations below ~70 K and the long-range magnetic ordering transition at TC = 43 K. Our results bring insight into the nature of the electronic states and lattice configurations in this intriguing mixed-valent Co oxide. |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y37.00003: Magnetic properties and magnetic structure of the frustrated quasi-one-dimensional antiferromagnet SrCuTe2O6 Pakornsak Saeaun, Yang Zhao, Pharit Piyawongwatthana, Taku J. Sato, Fangchang Chou, Maxim Avdeev, Ganatee Gitgeatpong, kittiwit Matan We will present results of magnetization measurements and neutron diffraction measurements to investigate a magnetic structure of the frustrated quasi-one-dimensional antiferromagnet SrCuTe2O6. The magnetization measurements on single-crystal cubic SrCuTe2O6 with an applied magnetic field along three inequivalent high symmetry directions [100], [110], and [111] reveal weak magnetic anisotropy. The results from a quantum Monte Carlo simulation on the Heisenberg spin-chain model, where the chain is formed via the dominant third-nearest-neighbor exchange interaction J3, yield the intrachain interaction (J3/kB) between 50.12(7) K for the applied field along [110] and 52.5(2) K along [100] with about the same g factor of 2.2. Single-crystal neutron diffraction unveils the transition to the magnetic ordered state as evidenced by the onset of the magnetic Bragg intensity at TN1 = 5.25(9)K. Based on irreducible representation theory and magnetic space group analysis of powder and single-crystal neutron diffraction data, the magnetic structure in the Shubnikov space group P4132, where the Cu2+ S = 1/2 spins antiferromagnetically align in the direction perpendicular to the spin chain, is proposed with the ordered moment of 0.52(6)μB. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y37.00004: Giant and highly anisotropic magnetocaloric effects in single crystals of disordered-perovskite RCr0.5Fe0.5O3 (R= Gd, Er) Hyunjun Shin, Jinseok Kim, Jonghyuk Kim, Donggun Oh, Nara Lee, Youngjai Choi We have synthesized disordered-pervoskite RCr0.5Fe0.5O3 (R=Gd, Er) single crystals and investigated the influences of magnetic anisotropy and additional ordering of rare-earth moments on the cryogenic magnetocaloric properties. Both GdCr0.5Fe0.5O3 (GCFO) and ErCr0.5Fe0.5O3 (ECFO) crystallize in an orthorhombic Pbnm structure with randomly distributed Cr3+ and Fe3+ ions. In GCFO, the long-range order of Gd3+ moments emerges at TGd = 11 K. The relatively isotropic nature of large Gd3+ moment originating from zero orbital angular moment exhibits giant and almost isotropic magnetocaloric effect with a maximum magneto entropy chagne as ΔSM ~ 50.0 J/kgK. On the contrary, in ECFO, the Er3+ moments tend to align along the c-axis below TEr = 12 K. The highly anisotropic magnetizations lead to a gaint rotating magnetocaloric effect demonstrated by a rotating magnetic entropy chagne ΔSR = 21.8 J/kgK. Due to the disordered characteristic of Cr3+ and Fe3+ ions in these compounds, the magnetocaloric properties appear to be determined principally by the magnetic anisotropic of rare-earth magnetic moments. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y37.00005: The Origin of Ising Magnetism in Ca3O2O6 Unveiled by Orbital Imaging Brett Leedahl, Martin Sundermann, Andrea Amorese, Andrea Severing, Hlynur Gretarsson, Lunyong Zhang, Alexander Komarek, Antoine Maignan, Maurits Wim Haverkort, Liu Tjeng One-dimensional CoO6 chains in Ca3Co2O6 give rise to an Ising-like magnetism with an intriguing quantum tunneling staircase structure in its magnetization. To resolve the underlying local electronic configuration of the Co ions in this material we applied s-core-level non-resonant inelastic x-ray scattering (s-NIXS), a new technique that is capable of imaging the shape of the 3d orbitals in real space. The orbital shapes that we found established that both Co sites (octahedral and trigonal prismatic) are in the 3+ valence state (i.e. 3d6); the trigonal Co site has a high-spin configuration, while the octahedral Co site is low spin. We directly "see" that it is the complex d2 orbital that is stabilized by the prismatic trigonal coordination, which naturally explains the Ising magnetism in the system. Utilizing this ability to image electron orbitals, and thus directly relating the orbital occupation with the local crystal structure—without the need for theoretical modeling—is essential for modeling magnetic properties. This is especially true in situations where one would like to make use of the delicate balance of competing interactions to stabilize a particular orbital state for a desired or optimized physical property. This work is published in Nature Communications. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y37.00006: A novel low temperature dynamic correlated paramagnet on a randomly diluted lattice Akmal Hossain, S. Kundu, Pranava Sivakumar, Ranjan Das, M. Baenitz, Peter J Baker, Jean-Christophe Orain, D. C. Joshi, Roland Mathieu, Priya Mahadevan, Sumiran Pujari, Subhro Bhattacharjee, Avinash Mahajan, Dipankar Das Sarma The presence of interacting spins on a lattice could lead to magnetically ordered states. However, magnetic frustration arising from competing exchange interactions could lead to such orderings being strongly suppressed, leading to quantum spin liquid-like states. An alternate approach to realize such exotic ground states is to introduce sufficient magnetic disorder in the lattice. Combining the two approaches, we explore a frustrated triangular lattice in presence of an extensive disorder such that the possibility of both spin liquid and spin glass states exist. Y2CuTiO6 has magnetically coupled spin- ½ Cu2+ on a triangular lattice in which 50% of the sites are randomly replaced by nonmagnetic Ti4+ atoms. We establish [1] that this system does not achieve either a magnetic ordering or a pure glassy state down to 50 mK, though the magnetic interaction strength is nearly 3000 times larger than this temperature. Various experiments and specific scaling behaviours of thermodynamic properties with temperature and magnetic fields suggest that the system remains in a disorder driven, dynamic cooperative paramagnetic state, opening new possibilities to explore the field of frustrated magnetism aided by disorder. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y37.00007: Magnetic Structure Characterization of Spinel Type High Entropy Oxide (MnFeCrCoNi)3O4 Graham Johnstone, Alannah M. Hallas High entropy oxides (HEOs) are crystallographically ordered compounds comprised of an equimolar proportion of five randomly distributed cations and a chemically ordered oxygen anion sublattice. In the formation of these crystals at high temperatures, the energy scale of configurational entropy rivals the enthalpy of formation for constituent oxide phases and minimizes the Gibbs free energy to produce a single-phase material. The discovery of long-range antiferromagnetic ordering in (MgCoNiCuZn)0.2O at TN = 113 K despite intense chemical disorder and a 40% magnetic dilution highlights the importance of studying magnetic order in these materials. More recently, there have been promising advancements in the synthesis of spinel type HEOs based on 3d transition metals. Here we presented a detailed structural and magnetic characterization of the spinel (MnFeCrCoNi)3O4 with the goal of elucidating the relationship between magnetism and chemical disorder. We verify the high entropy phase by Rietveld refinement and energy dispersive x-ray spectroscopy. Our magnetic susceptibility measurements reveal that this HEO transitions into a ferrimagnetic ordered state below 400 K. We will present the magnetic structure of (MnFeCrCoNi)3O4 determined from neutron diffraction. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y37.00008: Phase transition and magnetism in Fe-P-O-H based synthetic mineral Matthias Gutmann, Maria Poienar, Gavin Stenning, Carsten Paulmann, Martin Tolkiehn, Rudic Svemir, Pascal Manuel, Fabio Orlandi, Vaclav Petricek, Gheorghe Pascut Iron hydroxyl phosphates are minerals with rich crystal chemistry and potential applications in life sciences, where they can be used as effective catalysts, electrode materials, etc. Specific heat and susceptibility measurements combined with structural and magnetic studies performed on iron hydroxyl phosphates in the 2K - 470K temperature range, revealed an interesting non-magnetic monoclinic isostructural phase transition which will be discussed in terms of phenomenological Bond-Valence Model and Density Functional Theory with Embedded Dynamical Mean Field Theory (DFT+eDMFT). In addition, we will show the low temperature complex magnetic behavior, which is a consequence of the phase transition. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y37.00009: Role of Oxygen Vacancies in transposing the Electronic Properties of a Nonmagnetic Band Insulator KTaO3 Sanat Gogoi, Shashank Ojha, Manju Mishra Patidar, RANJAN PATEL, Prithwijit Mandal, Siddharth Kumar, Radhakrishnan Venkatesh, Vedachalaiyer Ganesan, Srimanta Middey, Manish Jain Potassium Tantalate (KTaO3) based 2-DEG is a potential platform for investigating spin-orbit coupling driven novel electronic and magnetic phenomena. In KTaO3 (KTO), oxygen vacancies emerge new exotic and collective behaviors like the observation of anomalous and topological Hall effect, an insulator to metal transition, etc. Our ab-initio calculations show that the isolated oxygen vacancies in KTO behave like a magnetic impurity, transforming the system from non-magnetic to a magnetic state. Noncollinear calculations reveal that isolated oxygen vacancies in KTO lead to non-trivial spin texture formation in real and momentum space. The local magnetic moments around the oxygen vacancies can cause skew scattering of the electrons, which originate the observation of the anomalous Hall effect in oxygen-deficient KTO. The ab-initio calculations also show that the oxygen vacancies tend to form a linear cluster around the Ta atoms. |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y37.00010: Structural and magnetic phases of rare-earth disilicates, R2Si2O7 Monica Ciomaga Hatnean, Oleg Petrenko, Martin Lees, Geetha Balakrishnan Rare-earth disilicates are interesting due to the variety of physical properties that they exhibit. The rich range of magnetic behaviors originates in the polymorphism exhibited by these materials. Recent reports showing that Yb2Si2O7 exhibits a quantum dimer magnet state motivated us to embark upon the investigation of some less-studied disilicate compounds, R2Si2O7 (R = Er, Ho and Tm). Previous studies show that Er2Si2O7 orders antiferromagnetically below TN = 1.9 K, as well as exhibiting a highly anisotropic magnetic behavior, however, the magnetic ground state of this compound is not yet established. To date, the magnetic properties of Ho2Si2O7 and Tm2Si2O7 have not been reported. Here, we present the results of our investigations to optimize the synthesis and crystal growth conditions of R2Si2O7 (R = Er, Ho and Tm), and also discuss the structural and magnetic properties of these materials. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y37.00011: magnetic structures and excitations in the series of A2PrO3 (A: alkali metals) mergen tunggiya, Kemp Plumb
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Friday, March 19, 2021 1:42PM - 1:54PM Live |
Y37.00012: Neutron scattering evidence of spin-liquid behavior in spinel compound CuGa2O4 Zhijun Xu, Aashish Sapkota, Guangyong Xu, Yimin Qiu, Matthew Brandon Stone, Genda Gu, John Tranquada We report neutron scattering measurements on a single crystal of CuGa2O4 sample. DC susceptibility shows no sign of ordering and elastic neutron measurements give no indication of magnetic order down to 0.1K. 3D measurements on low energy magnetic excitations show diffuse continuum intensity distributed about Brillouin zone boundary in momentum space at low temperature. The magnetic excitations extend up to at least 6 meV, and any gap must be smaller than 0.5 meV. With increasing temperature, the low energy magnetic excitation intensity gradually goes away, with a significant intensity reduction by 30 K. |
Friday, March 19, 2021 1:54PM - 2:06PM Live |
Y37.00013: Modification in the local atomic spin configuration drives an insulator to metallic phase transition in disordered double perovskites: the case of Nd2CoFeO6 Fernando Sabino, Leonardo S. de Oliveira, Daniel Z. Florio, Anderson Janotti, José A. Souza, Gustavo Dalpian The double perovskite (DP) Nd2CoFeO6 was recently synthetized presenting short-range magnetic interactions in temperatures below 540K, and a classic paramagnetic behavior above that temperature. In the paramagnetic phase, and for temperatures around 900 K, electrical resistivity measurements show a peculiar insulator to metallic transition, which could suggest a modification in the spin state of Co or Fe. Using DFT calculations, we address this curious phenomenon in the disordered Nd2CoFeO6. To model the complex structural and magnetic state of this DP, we used a supercell with 80 atoms and the quasi-random structure method to distribute the atoms and the magnetic moment of Co/Fe. We demonstrate a direct relation between the local magnetic moment of Co and the band gap of Nd2CoFeO6. In the most stable paramagnetic configuration, Co ions have a low spin configuration resulting in Nd2CoFeO6 with opened band gap. However, when the average Co magnetic moment increases, the band gap decreases. The modification in the spin state of Co ions spreads the unoccupied Co d orbitals in the band gap, resulting in the insulator to metallic phase transition. The energy difference from the insulator to the metallic configuration is around 70 meV, which agree very well to the experimental results. |
Friday, March 19, 2021 2:06PM - 2:18PM Live |
Y37.00014: Highly nonlinear magnetoelectric effect in antiferromagnetic Co4Ta2O9 single crystals Nara Lee, Donggun Oh, Sungkyun Choi, Jae Moon, Jong Hyuk Kim, Hyunjun Shin, Kwanghyo Son, Jürgen Nuss, Valery D Kiryukhin, Youngjai Choi Strongly correlated materials with multiple order parameters provide unique insights into the fundamental interactions in condensed matter systems and present opportunities for innovative technological applications . A class of antiferromagnetic honeycomb lattices compounds, A4B2O9 (A = Co, Fe, Mn; B = Nb, Ta), have been explored owing to the occurrence of linear magnetoelectricity. We observe a highly nonlinear magnetoelectric effect on single crystals of Co4Ta2O9 (CTO), distinctive from the linear behavior in the isostructural Co4Nb2O9. This observation of a strongly nonlinear magnetoelectricity suggests that two types of inequivalent Co2+ sublattices generate magnetic field-dependent ferroelectric polarization with opposite signs. These results motivate fundamental and applied research on the intriguing magnetoelectric characteristics of these honeycomb lattice materials. |
Friday, March 19, 2021 2:18PM - 2:30PM Live |
Y37.00015: Noncollinear antiferromagnetic order in the buckled honeycomb lattice of magnetoelectric Co4Ta2O9 determined by single-crystal neutron diffraction Sungkyun Choi, Donggun Oh, Matthias Gutmann, Shangke Pan, Gideok Kim, Kwanghyo Son, Jae Wook Kim, Nara Lee, Sang-Wook Cheong, Youngjai Choi, Valery D Kiryukhin Co4Ta2O9 is a newly interested magnetoelectric material with strong coupling. It exhibits unusual magnetoelectric effects, including sign change and non-linearity, which cannot be understood without detailed knowledge of the magnetic structure. |
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