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Revisiting the ground state of CoAl2O4: Comparison to the conventional antiferromagnet MnAl2O4

G. J. MacDougall, A. A. Aczel, Yixi Su, W. Schweika, E. Faulhaber, A. Schneidewind, A. D. Christianson, J. L. Zarestky, H. D. Zhou, D. Mandrus, and S. E. Nagler
Phys. Rev. B 94, 184422 – Published 17 November 2016

Abstract

The A-site spinel material CoAl2O4 is a physical realization of the frustrated diamond-lattice antiferromagnet, a model in which unique incommensurate or “spin-spiral-liquid” ground states are predicted. Our previous single-crystal neutron scattering study instead classified it as a “kinetically inhibited” antiferromagnet, where the long-ranged correlations of a collinear Néel ground state are blocked by the freezing of domain-wall motion below a first-order phase transition at T*=6.5 K. This paper provides new data sets from a number of experiments, which support and expand this work in several important ways. We show that the phenomenology leading to the kinetically inhibited order is unaffected by sample measured and instrument resolution, while new low-temperature measurements reveal spin correlations are unchanging between T=2 K and 250 mK, consistent with a frozen state. Polarized diffuse neutron measurements show several interesting magnetic features, which can be entirely explained by the existence of short-ranged Néel order. Finally, and crucially, this paper presents some neutron scattering studies of single crystalline MnAl2O4, which acts as an unfrustrated analog to CoAl2O4 and shows all the hallmarks of a classical antiferromagnet with a continuous phase transition to Néel order at TN=39 K. Direct comparison between the two compounds indicates that CoAl2O4 is unique, not in the nature of high-temperature diffuse correlations, but rather in the nature of the frozen state below T*. The higher level of cation inversion in the MnAl2O4 sample indicates that this behavior is primarily an effect of greater next-nearest-neighbor exchange.

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  • Received 29 June 2016

DOI:https://doi.org/10.1103/PhysRevB.94.184422

©2016 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

G. J. MacDougall1,2,*, A. A. Aczel2, Yixi Su3, W. Schweika4, E. Faulhaber3,5, A. Schneidewind5,6, A. D. Christianson2, J. L. Zarestky7, H. D. Zhou8,9, D. Mandrus10,11, and S. E. Nagler2,12

  • 1Department of Physics and Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
  • 2Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  • 3Jülich Centre for Neutron Science JCNS at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich GmbH, Lichtenbergstr. 1, D-85747 Garching, Germany
  • 4Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
  • 5Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner-Platz 1, D-14109 Berlin
  • 6Forschungsneutronenquell Heinz Meier-Leibnitz (FRM-II), D-85747 Garching, Germany
  • 7Division of Materials Science and Engineering, Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
  • 8Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
  • 9National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
  • 10Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
  • 11Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 USA
  • 12Bredesen Center, University of Tennessee, Knoxville, Tennessee 37996, USA

  • *gmacdoug@illinois.edu

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Issue

Vol. 94, Iss. 18 — 1 November 2016

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