Conference Agenda

Overview and details of the sessions of this conference. Please select a date or location to show only sessions at that day or location. Please select a single session for detailed view (with abstracts and downloads if available).

Please note that all times are shown in the time zone of the conference. The current conference time is: 1st Nov 2024, 12:27:31am CET

 
 
Session Overview
Session
MS-45: Frustrated magnetic order and emerging science
Time:
Wednesday, 18/Aug/2021:
10:20am - 12:45pm

Session Chair: Romain Sibille
Session Chair: Geetha Balakrishnan
Location: Club C

50 1st floor

Invited: Beauvois Ketty (France), Nicolas Gauthier (USA)


Session Abstract

The microsymposium focuses on the recent developments in the field of frustrated magnetism. Submissions are welcome in the field of (quantum) spin liquids, frustrated long-range orders and emerging properties (spin ices, chiral, zig-zag magnetic structures, spin-nematics, spin
liquids…).

 

For all abstracts of the session as prepared for Acta Crystallographica see PDF in Introduction, or individual abstracts below.

 


Introduction
Show help for 'Increase or decrease the abstract text size'
Presentations
10:20am - 10:25am

Introduction to session

Roman Sibille, Geetha Balakrishnan



10:25am - 10:55am

Dimer physics in the frustrated Cairo pentagonal antiferromagnet Bi2Fe4O9

Ketty Beauvois1,2, Virginie Simonet3, Sylvain Petit4, Julien Robert3, Frédéric Bourdarot2, Marin Gospodinov5, Sacha Mukhin6, Rafik Ballou3, Vassil Skumryev7, Eric Ressouche2

1Institut Laue Langevin, Grenoble, France; 2CEA, IRIG/DEPHY/MEM-MDN, Grenoble, France; 3Institut Néel, CNRS, Grenoble, France; 4CEA-CNRS, LLB Saclay, France; 5Institute of Solid State Physics, Bulgarian Academy of Sciences, Bulgaria; 6Russian Academy of science, Russia; 7Universitat Autonoma de Barcelona, Spain

The research field of magnetic frustration is dominated by triangle based lattices but exotic phenomena can also be observed in pentagonal networks. The Fe3+ ions in Bi2Fe4O9 materialize the first analogue of a magnetic pentagonal lattice [1]. The unit cell contains two different sites of four iron atoms each, which have different connectivities with the other irons (three or four neighbours for Fe1 and Fe2 respectively), and that form a lattice of pentagons. Because of its odd number of bonds per elemental brick, this lattice is prone to geometric frustration. The compound magnetically orders around 240 K: the resulting spin configuration on the two sites is the same, i.e. two orthogonal pairs of antiferromagnetic spins in a plane, with a global rotation between the two sites Fe1 and Fe2. This peculiar magnetic structure, which is the result of the complex connectivity and magnetic frustration, has opened new perspectives in the field of magnetic frustration.

In this original compound, we have measured the spin wave excitations in the magnetically ordered state by inelastic neutron scattering. The measurements have revealed an unconventional excited state related to local precession of pairs of spins. The confrontation of the experimental results with spinwave calculations allowed to determine the Hamiltonian of the system and shows a hierarchy of the interactions. This leads to a paramagnetic state constituted of strongly coupled antiferromagnetic pairs of spins (materializing isolated dimers) separated by much less correlated spins. This produces two types of response to an applied magnetic field associated with the two nonequivalent Fe sites, as observed in the magnetization density distributions obtained using polarized neutrons.

[1] E. Ressouche, V. Simonet, B. Canals, M. Gospodinov, V. Skumryev, Phys. Rev. Lett. 103, 267204 (2009)

External Resource:
Video Link


10:55am - 11:25am

Characterizing the local charge density to determine complex magnetic correlations, and vice versa

Nicolas Gauthier

Stanford University & SLAC National Accelerator Laboratory, Stanford, California 94305, USA

Crystal electric fields play an essential role in shaping the local electronic density of ions. For ions with strong spin-orbit coupling such as rare earths, this also results in defining the single-ion magnetic moment properties. Therefore, the study of crystal electric field levels is a common approach to establish the fundamental building blocks of the magnetic Hamiltonian. Indeed, the moment anisotropy and the single-ion wavefunction provide crucial information to describe complex magnetic materials such as spin liquids and multipolar systems [1,2]. In the first part of my presentation, I will illustrate this approach on the frustrated magnet SrDy2O4. This material exhibits two inequivalent zigzag chains of magnetic ions. The combination of low dimensionality and frustration inhibits long range order and only short range magnetic correlations are observed down to 60 mK [3]. Domain walls in the chains decay slowly and interchain interactions ultimately lead to their freezing, leading to a weakly fluctuating short range order [4]. The understanding of this complex behaviour could only be achieved from the knowledge of the moment anisotropies, established from the analysis of crystal field electric levels.

Above, we took advantage of strong spin-orbit coupling to determine magnetic properties by studying electric ones, i.e. the effect of crystal electric fields. This strong coupling between the electric charge and magnetic moment can also be used in the other direction: using magnetism to learn more about electric effects beyond the single-ion properties. As spin waves are collective excitations of the magnetic moments, the local charge densities can also sustain collective modes. Taking again the magnetic insulator SrDy2O4 as an example, I will demonstrate that neutron spectroscopy can measure these electric waves and that this observation is facilitated by the material’s magnetism. Interestingly, our results indicate that electric interactions dominate the magnetic interactions in this case, although they remain hidden to most measurement techniques. This observation encourages a reassessment of the description of rare-earth based magnets with unconventional properties.

[1] P. Santini, S. Carretta, G. Amoretti, R. Caciuffo, N. Magnani, G. H. Lander, Rev. Mod. Phys. 81, 807 (2009).

[2] R. Sibille, N. Gauthier, E. Lhotel, V. Porée, V. Pomjakushin, R. A. Ewings, T. G. Perring, J. Ollivier, A. Wildes, C. Ritter, T. C. Hansen, D. A. Keen, G. J. Nilsen, L. Keller, S. Petit & T. Fennell, Nat. Phys. 16, 546 (2020).

[3] A. Fennell, V. Y. Pomjakushin, A. Uldry, B. Delley, B. Prévost, A. Désilets-Benoit, A. D. Bianchi, R. I. Bewley, B. R. Hansen, T. Klimczuk, R. J. Cava & M. Kenzelmann, Phys. Rev. B 89, 224511 (2014).

[4] N. Gauthier, A. Fennell, B. Prévost, A.-C. Uldry, B. Delley, R. Sibille, A. Désilets-Benoit, H. A. Dabkowska, G. J. Nilsen, L.-P. Regnault, J. S. White, C. Niedermayer, V. Pomjakushin, A. D. Bianchi & M. Kenzelmann, Phys. Rev. B 95, 134430 (2017).

External Resource:
Video Link


11:25am - 11:45am

Magnetic structure and interactions in 2D layered van der Waals semiconductors CrPS4 and MnPSe3 probed with neutron scattering

Stuart Calder1, Amanda Haglund2, Yaohua Liu1, Daniel Pajerowski1, Huibo Cao1, Travis Williams1, Alexander Kolesnikov1, Vasile Garlea1, David Mandrus2

1Oak Ridge National Laboratory; 2University of Tennessee

Two-dimensional (2D) materials are of intense current fundamental and applied interest as a route to create novel fundamental phenomena beyond well-established classical behaviour within their topologically constrained layers. In this context 2D monolayer graphene, formed from the isolation of weakly connected van der Waals (vdW) bonded 2D layers in graphite by exfoliation, ignited widespread interest. Exotic quantum relativistic phenomena, such as Dirac semi-metals and quantum anomalous Hall insulators, have been predicted in graphene and related materials ranging from isolated 2D monolayers to quasi-2D bulk materials with vdW bonded layers. The focus has expanded to “beyond graphene” 2D vdW layered materials with intrinsic properties such as magnetism and semiconductivity not present in graphene, however the number of materials is limited and detailed understanding only just beginning.

MnPSe3 and CrPS4 are such layered vdW materials that are both magnetic and semiconducting, with magnetic ions forming hexagonal and rectangular 2D motifs. To access their low dimensional behaviour we probe bulk powder and single crystal samples with neutron scattering measurements [1,2]. Through magnetic symmetry analysis and spin wave analysis we are able to isolate and explore the 2D structural and magnetic behaviour in these bulk materials. Interactions shown in Fig. 1. The data highlights subtle competing interactions in both materials that leads to the stabilization of the determined magnetic ground states. These magnetic ground states were further tuned with small applied perturbations of field and temperature and found to undergo both subtle spin alterations and more dramatic metamagnetic transitions. The determination of the intralayer and interlayer exchange interactions and anisotropy within model spin Hamiltonians allowed the underlying observed exotic bulk behaviour to be explored.

The results show that for MnPSe3 the Se ion drives unexpectedly strong magnetic interactions between the 2D layers, which forms a contrast to the wider studies S analogue MnPS3. While for CrPS4 a further lowering of interaction dimensionality to 1D-chains is shown to be of significance. Collectively, these results highlight the subtle role of the crystalline structure on the emergent behaviour and show the powerful insights neutron scattering can supply to studies of low dimensional materials.

[1] S. Calder, A. Haglund, Y. Liu, D. M. Pajerowski, H. B. Cao, T. J. Williams, O. V. Garlea, D. Mandrus, “Magnetic structure and exchange interactions in the layered semiconductor CrPS4”, Physical Review B, Phys. Rev. B 102, 024408 (2020).

[2] S. Calder, A. Haglund, A. I. Kolesnikov, D. Mandrus, “Magnetic exchange interactions in the van der Waals layered antiferromagnet MnPSe3”, Physical Review B 103, 024414 (2021).

External Resource:
Video Link


11:45am - 12:05pm

Geometric frustration on the trillium lattice in a magnetic metal–organic framework

Johnathan M. Bulled1, Joseph A. M. Paddison2,3, Andrew Wildes4, Elsa Lhotel5, Breogan Pato-Doldan6, L. Claudia Gomez-Aguirre7, Paul J. Saines8, Andrew L. Goodwin1

1Inorganic Chemistry Laboratory, University of Oxford, South Parks Rd., Oxford OX1 3QR, U.K; 2Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, U.S.A.; 3Churchill College, University of Cambridge, Storey’s Way, Cambridge CB3 0DS, U.K.; 4Institut Laue-Langevin, BP156, 71 Avenue des Martyrs, 38000, Grenoble, France; 5Institut Néel, 25 Avenue des Martyrs, 38042 Grenoble, France; 6Department of Chemistry, University of Bergen, P.O. Box 7803, N-5020 Bergen, Norway; 7Department of Fundamental Chemistry and CICA, Faculty of Sciences University of A Coruña, 15071 A Coruña, Spain; 8School of Physical Sciences, University of Kent, Canterbury CT2 7NH, U.K.

In the dense metal-organic framework Na[Mn(HCOO)3], Mn2+ ions (S = 5/2) occupy the nodes of a ‘trillium’ net. We show that this material exhibits a variety of behaviour characteristic of geometric frustration: the Néel transition is suppressed well below the characteristic magnetic interaction strength; neutron scattering indicates that short-range magnetic order persists far above the Néel temperature; and the magnetic susceptibility exhibits a pseudo-plateau at 1/3-saturation magnetisation. We demonstrate that a simple nearest-neighbour Heisenberg antiferromagnet model accounts quantitatively for each observation, and hence Na[Mn(HCOO)3] is the first experimental realisation of this model on the trillium net. We demonstrate how both link geometric frustration within the classical spin liquid regime to a strong magnetocaloric response at low fields.

External Resource:
Video Link


12:05pm - 12:25pm

Investigating Kosterlitz-Thouless physics in the triangular lattice antiferromagnet TmMgGaO4

Benjamin A. Frandsen1, Zhiling Dun2, Raju Baral1, Martin Mourigal2

1Brigham Young University, Provo, United States of America; 2Georgia Institute of Technology, Atlanta, United States of America

The transverse-field Ising model on a triangular lattice is predicted to support a topological Kosterlitz-Thouless (KT) phase at nonzero temperature through a mapping of the Ising spins to a complex order parameter defined for each triangular unit. Recently, the triangular lattice antiferromagnet TmMgGaO4 has emerged as a candidate material to realize this theoretical scenario. Through the complementary use of neutron diffraction and magnetic pair distribution function (mPDF), we have quantitatively investigated the spin correlations in TmMgGaO4 in the temperature region of interest, tracking their evolution across the proposed transitions into and out of the KT phase. We confirm the presence of the three-sublattice order predicted for the ground state and show that the local magnetic structure undergoes distinct changes in the temperature range expected for the KT phase. Modeling the real-space mPDF reveals a preferential tendency for the system to form bound vortex-antivortex pairs, the hallmark of the KT phase, precisely in the expected temperature range. These findings constitute promising evidence for the KT phase, potentially establishing TmMgGaO4 as a rare platform for studying KT physics in a dense spin system.

External Resource:
Video Link


12:25pm - 12:45pm

Nanoscale distortions and ground state selection in geometrically frustrated magnets

Alexandros Lappas1, Benjamin Frandsen2, Emil Bozin3

1Foundation for Research and Technology - Hellas, 71110 Heraklion, Crete, Greece; 2Brigham Young University, Provo, Utah 84602, USA; 3Brookhaven National Laboratory, Upton, New York 11973, USA

Geometrically frustrated magnets, such as triangular networks of antiferromagnetically coupled spins, can display incredibly rich physical properties that may have potential applications in quantum information science and other technologies. Determining if and how magnetic order emerges from competing magnetic tendencies is an important objective in this field. Here, we discuss the Jahn-Teller active triangular AMnO2 (A= Na, Cu; Fig. 1) antiferromagnets [1] to highlight that the degree of frustration, mediated by residual disorder, contributes to the rather differing pathways towards a single, stable magnetic ground state, albeit with varying ordering temperatures. For these insulating sister compounds, complementary high-resolution synchrotron XRD, local-probe muon-spin relaxation (μ+SR) studies, corroborate that the layered NaMnO2 adopts a remarkable magnetostructurally inhomogeneous ground state. [2] In view of this peculiarity, we employ powerful neutron total scattering and magnetic pair distribution function (PDF) analysis to uncover that although CuMnO2 undergoes a conventional symmetry-lowering lattice distortion driven by Néel order, in the Na-derivative a short-range triclinic distortion (Fig. 2) lifts the degeneracy of the isosceles triangular network on the nanoscale, thereby enabling long-range magnetism to develop with enhanced magnetic correlations above the transition. [3] More generally, the work illuminates the cooperative intertwining of the local atomic and magnetic structures that permits ground state selection when spatial inhomogeneity meets geometrical frustration, a mechanism that may also be operative in other frustrated materials with electronically active transition metal cations.

[1] M. Giot et al., Phys. Rev. Lett. 99, 247211 (2007).

[2] A. Zorko et al., Sci. Rep. 5, 9272 (2015).

[3] B. A. Frandsen et al., Phys. Rev. B 101, 024423 (2020).

External Resource:
Video Link


 
Contact and Legal Notice · Contact Address:
Privacy Statement · Conference: IUCr 2021 | August 14 - 22, 2021 | Prague, Czech Republic
Conference Software: ConfTool Pro 2.8.103+TC+CC
© 2001–2024 by Dr. H. Weinreich, Hamburg, Germany