Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session X46: 3D Frustrated Magnets: Other GeometriesFocus
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Sponsoring Units: GMAG DMP Chair: Jeremy Carlo, Villanova Univ Room: 708 |
Friday, March 6, 2020 11:15AM - 11:51AM |
X46.00001: Frustrated Magnetism in Mott Insulating V2O3 Invited Speaker: Harald Jeschke The phase diagram of V2O3 as function of transition metal doping and temperature is famous for showing transitions between metallic and insulating and between paramagnetic and antiferromagnetic phases. In particular, the Mott metal-insulator transition which is induced by a few percent of chromium doping has been studied intensively. Using a combination of density functional theory calculations and inelastic neutron scattering experiments, we study the magnetic interactions in the chromium-stabilized antiferromagnetic and paramagnetic insulating phases as function of temperature [1]. The calculations based on an energy mapping technique [2] are performed for low temperature monoclinic and high temperature rhombohedral structures. Both calculations and INS cross sections reveal significant magnetic frustration and degeneracy of the paramagnetic insulating phase which is relieved by the rhombohedral-to-monoclinic transition at TN=185 K. Magnetic frustration can be shown to be present in rhombohedral (V1−xCrx)2O3 for a large range of dopings. This suggests that magnetic frustration plays an important role in suppressing the magnetic long-range-ordering temperature and thereby exposing a large phase space for the paramagnetic Mott metal-insulator transition. |
Friday, March 6, 2020 11:51AM - 12:03PM |
X46.00002: Magnetic Field Induced Phase Transition in Spinel GeNi2O4 Tathamay Basu, Tao Zou, Z Dun, Clarina Reloj Dela Cruz, Tao Hong, Huibo Cao, Mengze Zhu, Haidong Zhou, Xianglin Ke Cubic spinel GeNi2O4 exhibits intriguing magnetic properties with two successive antiferromagnetic phase transitions (~12 and 11 K) in the absence of structural distortion. By means of heat capacity and magnetic susceptibility measurements, we have revealed a new magnetic phase in presence of magnetic field field (≥ 4 T) along the [111] direction, which is not observed when the magnetic field is applied along the [100] and [110] directions. Neutron powder diffraction measurements confirm such a field-induced phase transition and suggest it be ascribed to a spin reorientation in presence of magnetic field. We will discuss the potential mechanisms regarding such a peculiar magnetic anisotropy in this cubic system. |
Friday, March 6, 2020 12:03PM - 12:15PM |
X46.00003: Characterization of the crystal field scheme of a new family of geometrically frustrated rare earth spinels. Dalmau Reig-i-Plessis, Greg MacDougall, Adam Aczel, Alexandra Cote, Sean van Geldern The pyrochlore lattice is known for having a large variety of exotic, frustration-driven phases, the specifics of which are determined by the symmetry of the local moments and their interactions. Here we present on a new family of compounds MgRE2Se4 (RE = Ho, Tm, Er, and Yb), which form in the spinel structure, were the rare earth atoms are a pyrochlore sublattice. In this presentation we will show inelastic neutron scattering measurements of the crystal electric field (CEF) excitations. We fit this neutron data to find the most likely CEF Hamiltonian for each compound in the family and comment on the possible consequences of the result. We show that MgTm2Se4 has a spin singlet ground ground state with a low lying signlet excited state, similar to an Ising moment in a transverse field. MgHo2Se4 has an Ising ground state with several additional thermally accessible levels. MgEr2Se4 is shown to have Ising moments and is a spin ice compound. MgYb2Se4 is shown to be an effective spin 1/2 system with strong spin anisotropy. |
Friday, March 6, 2020 12:15PM - 12:27PM |
X46.00004: Update on the Magnetic and Structural Properties of the Solid Solutions CuAl2(1-x)Ga2xO4 Thomas Bullard, Michael Susner, Keith Taddei, Jacilynn Brant, Timothy Haugan Magnetic frustration continues to be an area of interest due to its association with the emergence of novel magnetic ground states such as spin glasses. Two systems that have been identified as spin glasses are the spin ½ antiferromagnetic spinels CuAl2O4 and CuGa2O4. In this research we examine the solid solution between these two end members, CuAl2(1-x)Ga2xO4. The solution displays magnetic glassy properties such as bifurcation in the FC - ZFC DC susceptibility, a frequency dependence of the freezing temperature, memory effects, and slow relaxation. Whether the system is better classified as a cluster glass or insulator spin glass will be discussed. Further, we observe an increase in the magnetic frustration as Ga3+ is replaced with Al3+. We have examined the atomic occupancy of the even members of the solid solution via neutron and synchrotron diffraction. As Ga+3 is replaced with Al+3 we find an increase in frustration as the magnetic Cu+2 ion shifts from the octahedral to the tetrahedral sublattice. |
Friday, March 6, 2020 12:27PM - 12:39PM |
X46.00005: Mean field theory for cooperative magnetism in non-Kramers garnets Bruno Tomasello, Rafal Wawrzynczak, Göran Nilsen, Tom Fennell, Tim Ziman Kramers’ theorem entails a fundamental symmetry valid only for odd-electron systems, i.e. any eigenstate and its time-reversed counterpart belong to the same spectrum. Notwithstanding, the magnetic states of non-Kramers ions, which have even number of electrons, can be constrained because of time-reversal symmetry. Indeed, if the low-lying singlets of a crystal of such ions are well gapped from the eigenstates at higher energies, then the magnetic moments at low-temperatures can only be axially anisotropic and only magneto-striction can account for low energy fluctuations. Rare-earth garnets are a suitable playground for studying the competition of magnetic frustration, magneto-elasticity, induced magnetic ordering, and the role of nuclear moments. This talk presents our current theoretical understanding of the non-Kramers garnet Tb3Ga5O12, benefitting from state of the art neutron scattering experiments for the crystal-field and magnetic structure – PRB,100,094442(2019). The discussion highlights the mean-field theory proposed in the 70s by Hammann & Manneville for the induced magnetic ordering found in both Tb3Ga5O12 and Ho3Ga5O12. We contrast our study to the work of Paddison et al. on the magnetic ordering and excitations of the non-Kramers Ho3Ga5O12 – arXiv:1908.03530(2019). |
Friday, March 6, 2020 12:39PM - 12:51PM |
X46.00006: Absence of long-range magnetic ordering in the S=1/2 frustrated system Ca3Cu2GeV2O12 Christopher Wiebe, Joey A. Lussier, Brooke Richtik, Cole D Mauws, Jeffrey Lynn Quantum spin liquids can be found in materials with a combination of geometric frustration along with low spin. Due to its spin of S=1/2, the copper (II) ion is often present in the discussion of new spin liquid candidates. The solid state compound Ca3Cu2GeV2O12 is a material that crystallizes in the garnet structure (space group #230, Ia-3d), where 3-dimensional frustration from competing exchange interactions is known to occur. Heat capacity measurements have shown a lack of sharp ordering transitions in this compound down to 0.35 K, which is confirmed with a lack of long-range magnetic order via neutron diffraction measurements to 0.07 K. This system displays a Weiss temperature of -0.93(1) K indicating net antiferromagnetic interactions and significant J1-J2 competition causing frustration. Using both neutron and X-ray diffraction along with heat capacity and magnetometry, the work presented here shows that Ca3Cu2GeV2O12 has potential as a new spin liquid candidate. |
Friday, March 6, 2020 12:51PM - 1:03PM |
X46.00007: Magnetic order and single-ion anisotropy in Tb3Ga5O12 rare-earth garnet. Rafal Wawrzynczak, Bruno Tomasello, Pascal Manuel, Dmitry Khalyavin, Duc Le, Tatiana Guidi, Antonio Cervellino, Tim Ziman, Martin Boehm, Göran Nilsen, Tom Fennell Terbium gallium garnet(TGG), Tb3Ga5O12 exhibits complex low-temperature magnetism, that involves frustration, single-ion anisotropy and induced-moment type ordering. Tb3+ magnetic ions form two interpenetrating half-garnet lattices – three-dimensional arrangements of corner-sharing triangles. The low-symmetry local environment of Tb3+ sites provides a complete lifting of the degeneracy within the lowest crystal electric field (CEF) manifold. The resulting ground-state observed with inelastic neutron scattering is a quasidoublet comprised of two closely-lying singlets. The spectroscopic data allowed for refinement of the CEF Hamiltonian parameters and retrieval of its eigenstates. Despite the singlet ground-state TGG orders magnetically at TN=0.25 K, much lower than |θCW|=8 K given by the bulk susceptibility. Neutron powder diffraction has shown the ordered structure to be of a multiaxial antiferromagnet type with strong single ion anisotropy. The results of powder magnetization measurements are in good agreement with values based on the CEF model down to 20 K, where the onset of magnetic correlations is seen. Also, a strong temperature-dependence of the quasidoublet ground-state is found. These observations suggest existence of a correlated paramagnet regime of unknown nature. |
Friday, March 6, 2020 1:03PM - 1:15PM |
X46.00008: Field dependence of magnetic order in frustrated diamond-like antiferromagnet LiYbO2 Mitchell Bordelon, Lorenzo J Posthuma, Eric M Kenney, Nicholas Butch, Craig Brown, Arnab Banerjee, Michael John Graf, Stephen Wilson Frustrated magnetism is a hotbed for searching for new electronic phases of matter. This can theoretically lead to states such as the spiral spin liquid where coplanar degenerate spiral states contain coherently fluctuating spins. One proposed venue for this state has been in the cubic diamond lattice arising from frustration in a J1-J2 Hamiltonian. Here we propose a new materials system where spiral spin liquids may potentially be observed based upon a tetragonally-elongated diamond lattice. This is exemplified by effective J = 1/2 moments within LiYbO2 via a combination of low-energy inelastic neutron scattering, crystalline electric field analysis, and linear spin wave theory. Magnetic order and its evolution under magnetic field will be discussed. |
Friday, March 6, 2020 1:15PM - 1:27PM |
X46.00009: Terahertz spectroscopy on breathing pyrochlore LiGaCr4S8 YUFEI Li, Evan Jasper, Ganesh Pokharel, Andrew D Christianson, David Mandrus, Rolando Valdes Aguilar A breathing pyrochlore lattice has alternating tetrahedra of different sizes, in which there exist different interactions. The competition of these interactions could lead to some interesting phenomena, for example, magnetic frustration and magnetoelastic coupling [1]. |
Friday, March 6, 2020 1:27PM - 1:39PM |
X46.00010: Single Crystal Growth and Magnetic-Thermal Characterization of a Rare-Earth Based Breathing Pyrochlore Family Rabindranath Bag, Lalit Yadav, Zhenzhong Shi, Sachith Dissanayake, David E Graf, Eun Sang Choi, Franz Lang, Catalina Salazar Mejia, Elizabeth Green, Stephen Blundell, Sara Haravifard The Breathing Pyrochlore (BP) lattice, which consists of three dimensionally corner sharing tetrahedra with alternating sizes, has recently attracted much attention due to presence of frustrated or competing interactions. BP system has also been proposed to host of many intriguing phenomena such as Quantum Spin Liquid, Quantum Spin Ice and Weyl magnons, due to anisotropic spin-spin interactions [1-3]. Large and high quality single crystals of BP compounds are highly needed, in order to advance these hypotheses experimentally. We have successfully grown single crystals of a rare-earth BP family, using the uniquely modified travelling solvent floating zone techniques. Additionally, we have performed specific heat, thermal conductivity, AC /DC magnetic susceptibility, magnetization, magneto-dielectric, μSR and X-ray diffraction measurements to probe the physical properties of these new compounds. In this talk I will present the results of our single crystal growth and characterization efforts. |
Friday, March 6, 2020 1:39PM - 1:51PM |
X46.00011: Field Dependent Neutron Scattering Studies of Breathing Pyrochlore Ba3Yb2Zn5O11 Sachith Dissanayake, William Steinhardt, Zhenzhong Shi, Stephen J Kuhn, Jeffrey Rau, Nicholas Butch, Matthias D Frontzek, Andrey Podlesnyak, Yiming Qiu, Wangchun Chen, David E Graf, Tao Hong, Casey Marjerrison, Michel J P Gingras, Sara Haravifard Breathing pyrochlore systems are composed of corner-sharing tetrahedra of different sizes pointing in opposing directions, leading to different intra- and inter-tetrahedra exchange interactions and the emergence of the Dzyaloshinskii-Moriya interaction due to loss of inversion symmetry. They are predicted to host exotic physics including quantum spin ice, quantum spin liquid, and field-tunable Weyl magnons. In this talk we will present single-crystal field-dependent unpolarized and polarized inelastic neutron scattering measurements on Yb-based breathing pyrochlore system, as well as a theoretical model that can effectively describe some of our experimental findings. |
Friday, March 6, 2020 1:51PM - 2:03PM |
X46.00012: Neutron Scattering Studies of Rare-Earth Based Breathing Pyrochlore System. Lalit Yadav, Rabindranath Bag, Sachith Dissanayake, Zhenzhong Shi, Guangyong Xu, Hui Wu, Craig Brown, Nicholas Butch, Franz Lang, Stephen Blundell, Sara Haravifard
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