Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F46: Pyrochlores IFocus
|
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Jinguang Cheng, Chinese Academy of Sciences Room: 708 |
Tuesday, March 3, 2020 8:00AM - 8:12AM |
F46.00001: Spherical Neutron Polarimetry and the Phase Diagram of Magnetically Dilute Er2Ti2O7 Connor Buhariwalla, Jonathan Gaudet, Cissy Suen, Navid Qureshi, Anne Stunault, Timothy Munsie, Hanna Dabkowska, Bruce D. Gaulin The ground state of XY pyrochlore antiferromagnet Er2Ti2O7 has been a rich topic of research due to the selection of a non-coplanar k=0 magnetically ordered state ψ2 through order by disorder. Several proposed mechanisms account for this selection of ψ2 over the coplanar ψ3, the alternate basis state of the Γ5 irreducible representation. Recent theory work has proposed that magnetic dilution that will lead to an instability in the ground state selection, resulting in a ψ3 ground state for a dilute Er2Ti2O7. Through systematic substitution of non-magnetic Y3+ on the Er3+ site, we have probed the effect of such dilution with samples of 5%, 10%, and 20% Y3+. While the magnetic structures of ψ2 and ψ3 are indistinguishable in an unpolarized neutron scattering measurement, the contrast is clear using spherical neutron polarimetry(SNP). In this talk, I will present the results of our SNP study of these 3 diluted samples, following our previous work using inelastic neutron scattering. |
Tuesday, March 3, 2020 8:12AM - 8:24AM |
F46.00002: Magnetic phase competition in the rare-earth pyrochlore Er2Sn2O7 Danielle R Yahne, Liurukara D Sanjeewa, Joseph Kolis, Ludovic DC Jaubert, Darren Pereira, Matthew John Enjalran, Michel J P Gingras, Kate Ross Rare-earth pyrochlore oxides (A2B2O7) can host a wealth of exotic phenomena due to geometric- and exchange-frustration. Er2Sn2O7 is especially interesting in this regard as, based on available estimates of the exchange interactions, it lies near a phase boundary in the anisotropic exchange parameter space, between two antiferromagnetic states: the Palmer-Chalker states (where Er2Sn2O7 orders) and the Γ5 states. A natural tool to probe such multi-phase competition is the application of an external magnetic field, but until now the absence of single crystals made such approach difficult to analyze. In this talk, we report specific heat measurements on single crystals of Er2Sn2O7 under fields applied along the three high symmetry directions, [111], [110], and [100]. Each field direction provides a distinct phase diagram, but with the shared feature that one (sometimes even two) reentrant lobe(s) appear above a threshold field of 0.2 T. The nature of this reentrance can be understood semi-quantitatively through classical Monte-Carlo simulations and mean field theory, the details of which will be described in a presentation by D. Pereira. |
Tuesday, March 3, 2020 8:24AM - 8:36AM |
F46.00003: Theory of Multiple Reentrant Phenomena in the XY Pyrochlore Er2Sn2O7 Darren Pereira, Ludovic DC Jaubert, Matthew John Enjalran, Danielle Yahne, Kate Ross, Michel J P Gingras Rare-earth pyrochlore magnets are known to exhibit a variety of exotic phenomena. The dipolar XY pyrochlore magnets in particular act as playgrounds for effects like order-by-disorder, multiphase competition, and strong quantum fluctuations. Er2Sn2O7, a member of the XY pyrochlore family, has recently been synthesized as a single crystal and studied under a magnetic field. The resulting (H,T) phase diagram reveals multiple reentrant lobes for fields applied in the [100], [110], and [111] directions. In this talk, I will discuss our efforts to understand these reentrant phenomena from the theoretical front, drawing from variational mean-field theory, classical Monte Carlo simulations, and classical spin wave analysis. I will argue that the reentrant lobes are related to a complex multiphase competition, in which the changing ground state degeneracy in a field is associated with the apparition of soft mode excitations. We expect our reasoning to be applicable to other rare-earth pyrochlores and frustrated magnets in general, especially for systems with a discrete ground state degeneracy. |
Tuesday, March 3, 2020 8:36AM - 9:12AM |
F46.00004: High pressure synthesis and characterization of R2Pt2O7 pyrochlores Invited Speaker: Jinguang Cheng Rare-earth pyrochlore oxides R2B2O7 constitute a versatile material platform to study a wide range of magnetic phenomena including order by disorder, geometric frustration, spin ice, and spin freezing. While being non-magnetic, the B-site cations are thought to be able to influence the magnetic properties of these compound primarily through the chemical pressure, which has been well demonstrated in the comparative studies of R2B2O7 (B = Ge, Ti, Sn) through varying the radius of the B-site cation. The high-pressure synthesis of R2Ge2O7 with the cubic pyrochlore structure is essential for these studies. Recently, we have further extended our research to the R2Pt2O7 system, which can only be stabilized under high-pressure conditions. Unlike the previously studied R2B2O7 with the B site occupied by either a 3d transition-metal like Ti or a p-block metal such as Ge and Sn, the Pt4+ has spatially more extended 5d orbitals and thus enhanced Pt 5d-O 2p hybridizations that might modify the local anisotropic exchange interactions of R3+ ions. Such an effect beyond the steric effect has not been taken into account in previous studies on the geometrically frustrated magnets. Indeed, we found enhanced magnetic ordering temperature in Gd2Pt2O7 due to presence of extra superexchange pathways through the empty Pt-eg orbitals [1]. We also revealed distinct influences on the anisotropic exchange interactions in the XY pyrochlores Er2Pt2O7 and Yb2Pt2O7 [2]. In addition, we observed unusual behaviors in the classical spin ice Ho2Pt2O7 [3]. |
Tuesday, March 3, 2020 9:12AM - 9:24AM |
F46.00005: Single crystal neutron scattering study of the pyrochlore Yb2Ge2O7 Colin Sarkis, Jeffrey Rau, Duminda Sanjeewa, Matthew Powell, Joseph Kolis, Jonathan J Marbey, Stephen Hill, Jose Rodriguez-Rivera, Harikrishnan S Nair, Michel J P Gingras, Kate Ross Rare earth pyrochlore oxides have been found to be hosts for a wide breadth of exotic phenomena based on strong frustration. Previous single crystal studies of Yb2Ti2O7 have established that it forms a ferromagnetic (FM) ground state, but lies near a classical phase boundary between FM and antiferromagnetic (AFM) states. Meanwhile, powder neutron scattering studies of Yb2Ge2O7 show it selects the AFM state. Despite this difference, these Yb pyrochlores share the same unusual spin dynamics in zero field. Further experimental progress on Yb2Ge2O7 has been stymied by a lack of large single crystal samples. We report inelastic neutron scattering measurements on single crystals of Yb2Ge2O7 grown by a hydrothermal method. We have used the field-polarized spin waves to determine the exchange parameters for Yb2Ge2O7. The g-tensor was independently determined from electron paramagnetic resonance on a Lu1.98Yb0.02Ge2O7 sample in order to enable an unambiguous determination of these parameters. Our analysis and theoretical modeling show that Yb2Ge2O7 lies in extreme proximity to the classical phase boundary between the AFM and FM phase, lending strong support to the notion of phase competition as playing a key role in the Yb pyrochlore family. |
Tuesday, March 3, 2020 9:24AM - 9:36AM |
F46.00006: Orientation Dependence of the Magnetic Phase Diagram of Yb2Ti2O7 Steffen Säubert, Allen Scheie, Christopher Duvinage, Jonas Kindervater, Shu Zhang, Hitesh Changlani, Guangyong Xu, Seyed Koohpayeh, Oleg Tchernyshyov, Collin Leslie Broholm, Christian Pfleiderer We present the orientation dependence of the magnetic phase diagram of stoichiometric Yb2Ti2O7 using four experimental probes: magnetization, heat capacity, susceptibility, and neutron scattering. The magnetic phase diagram for fields along 〈110〉 shows dramatic reentrant character (similar to fields along 〈111〉), whereas for fields along 〈100〉, the upper phase boundary collapses and the system enters a field polarized state for small applied fields. By comparing this data to theoretical models, we show that Yb2Ti2O7 is a cubic ferromagnet that is qualitatively described by Landau theory, but a comparison of upper critical fields show that the system cannot be described only by classical mean-field considerations, more that it is subject to collective or quantum effects. |
Tuesday, March 3, 2020 9:36AM - 9:48AM |
F46.00007: Exploring the influence of disorder on magnetic moment fragmentation Eli Zoghlin, Julian L Schmehr, Stephen Wilson Recent neutron scattering measurements demonstrating concurrent all-in-all-out antiferromagnetic order and pinch-point diffuse scattering in the pyrochlore Nd2Zr2O7 provide compelling evidence for the phenomenon of magnetic moment fragmentation1. However, the influence of chemical and crystallographic disorder native to the pyrochlore lattice on the formation of this underlying state remains poorly understood. Here we present an experimental exploration of the role of native disorder on the features associated with spin fragmentation in Nd2Zr2O7. Neutron scattering and thermodynamic measurements of crystals with varying defect concentrations, examined by electron microprobe analysis, are studied to resolve the impact of disorder on the ground state of this material. |
Tuesday, March 3, 2020 9:48AM - 10:00AM |
F46.00008: Magnetization plateaus of the quantum pyrochlore Heisenberg antiferromagnet SANTANU PAL, SIDDHARTHA LAL We predict magnetization plateaus ground states for S = 1/2 Heisenberg antiferromagnets on pyrochlore lattices by formulating arguments based on gauge and spin-parity transformations. We derive a twist operator appropriate to the pyrochlore lattice, and show that it is equivalent to a large gauge transformation. Invariance under this large gauge transformation indicates the sensitivity of the ground state to changes in boundary conditions. This leads to the formulation of an Oshikawa-Yamanaka-Affleck–like criterion at finite external magnetic field, enabling the prediction of plateaus in the magnetization versus field diagram. We also develop an analysis based on the spin-parity operator, leading to a condition from which identical predictions are obtained of magnetization plateaus ground states. Both analyses are based on the non-local nature of the transformations, and rely only on the symmetries of the Hamiltonian. This suggests that the plateaus ground states can possess properties arising from non-local entanglement between the spins. |
Tuesday, March 3, 2020 10:00AM - 10:12AM |
F46.00009: Magnetism of classical pyrochlore antiferromagnet Na3Mn(CO3)2Cl Kazuhiro Nawa, Daisuke Okuyama, Maxim Avdeev, Hiroyuki Nojiri, Masahiro Yoshida, Daichi Ueta, Hideki Yoshizawa, Taku Sato Pyrochlore antiferromagnets have attracted interests in terms of unconventional ground states and spin excitations owing to competing interactions. When its magnetism is dominated by classical spins coupled by Heisenberg interactions, a spin liquid state is expected as its ground state because of infinite degeneracy in the ground state (R. Moessner and J. T. Chalker, Phys. Rev. Lett. 80, 2929 (1998); Phys. Rev. B 58, 12049 (1998).). In this research, we report structural and magnetic properties together with low-temperature neutron diffraction patterns on a new pyrochlore antiferromagnet Na3Mn(CO3)2Cl. The structure of Na3Mn(CO3)2Cl is isotypic with that of the Co-analogue Na3Co(CO3)2Cl, which exhibits all-in-all-out magnetic order below 1.5 K (Z. Fu et al., Phys. Rev. B 87, 214406 (2013)). On the other hand, no magnetic Bragg peak indicating a magnetic order was detected down to 0.05 K in Na3Mn(CO3)2Cl. A high degeneracy near the ground state is suggested by a magnetic entropy estimated from heat capacity experiments and enhancement of diffuse scattering from neutron diffraction experiments. |
Tuesday, March 3, 2020 10:12AM - 10:24AM |
F46.00010: Magnetic properties of distorted pyrochlore lattice Mn2(OD)3X (X = Cl, Br) Masato Hagihala, X.G. Zheng, Takashi Kamiyama Atacamite family, of which component is M2(OH)3X (M:3dmetal, X:halogen) forms geometrical frustrated lattice, and behave in an exotic magnetic states; the ground state of clinoatacamite is coexistence of long-range order and strong spin fluctuation[1]. Atacamite(Cu2(OH)3Cl), which is distorted pyrochlore, reported as antiferromagnetic transition at TN = 9 K[2]. Recently, it is reported that atacamite is regarded as S =1/2 sawtooth chains system, and its magnetic order is represented k = (1/2 0 1/2) [3,4]. We remark atacamite type compounds Mn2(OH)3X. Both compounds have two successive transitions below T ~ 3K [5]. Our neutron experiment revealed different magnetic orders on these four phases. The ground state of Mn2(OD)3Br is also represented k = (1/2 0 1/2), its magnetic structure have two kind of spin configurations on the saw tooth chains. Spin configurations on other three phases are modulated along the a axis. Successive transition and different k vector imply stronger frustration effect than atacamite. [1] X. G. Zheng et al., PRL 95, 057201 (2005). [2] X. G. Zheng et al., PRB 71, 174404 (2005). [3] L. Heinze et al., Pyhsica B 536, 377-378 (2018). [4] L. Heinze et al., arXiv:1904.07820v1. [5] M. Hagihala et al., J. Phys.: Cond. Matt. 19, 145281 (2007). |
Tuesday, March 3, 2020 10:24AM - 10:36AM |
F46.00011: Magnetometry and transport studies of single crystal pyrochlore iridates Matthew Pearce, Kathrin Goetze, Paul Goddard, Martin Lees, Dharmalingam Prabhakaran, Andrew T Boothroyd, Tycho Sikkenk, Attila Szabo, Claudio Castelnovo Magnetic pyrochlore oxides have attracted significant interest due to their geometrically frustrated lattice, which acts to suppress long range magnetic order and leads to a variety of unusual magnetic ground states and exotic excitations. |
Tuesday, March 3, 2020 10:36AM - 10:48AM |
F46.00012: Magnetisation and monopole density response to applied magnetic fields in rare earth pyrochlore iridates Attila Szabo, Tycho Sikkenk, Claudio Castelnovo, Matthew Pearce, Kathrin Goetze, Martin Lees, Dharmalingam Prabhakaran, Andrew T Boothroyd, Paul Goddard We investigate the behaviour of rare earth pyrochlore iridates Dy2Ir2O7 and Ho2Ir2O7 using dipolar Monte Carlo simulations for the rare earth moments and an effective representation of the Ir moments as local fields [Lefrancois et al, Nat. Comm. 2017]. We study in particular how the magnetisation and defect population respond to externally applied magnetic fields along different crystal directions. We uncover an intriguing interplay between the rare earth moments and the correlations in the underlying Ir moments, and we comment on their possible relevance to experimental results. |
Tuesday, March 3, 2020 10:48AM - 11:00AM |
F46.00013: Study of the spin orbit coupling metal Cd2Re2O7 by torque magnetometry Kuan-Wen Chen, Tomoya Asaba, Ziji Xiang, Colin B Tinsman, Lu Chen, Jiaqiang Yan, Lu Li
|
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700