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Title: Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr 2 O 4

In spinels ACr 2O 4(A=Mg,Zn), realization of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition at T N=12.5 K. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberg et al. [Pow. Diff. 17, 230 (2002)], while other features depend on sample or cooling protocol. A complex, partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectors k 1=($$\frac{1}{2}$$ $$\frac{1}{2}$$ 0),k 2=(1 0 $$\frac{1}{2}$$) appear. The ordered moment reaches 1.94(3) μ B/Cr 3+ for k 1 and 2.08(3) μ B/Cr 3+ for k 2, if equal amount of the k 1 and k 2 phases is assumed. The magnetic arrangements have the dominant components along the [110] and [1-10] diagonals and a smaller c component. We use inelastic neutron scattering to investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. Finally, the distinctive fingerprint of clusterlike excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [5] ;  [6] ; ORCiD logo [7] ; ORCiD logo [7] ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] more »;  [13] « less
  1. Paul Scherrer Inst., Villigen (Switzerland). Lab. for Neutron Scattering and Imaging
  2. Univ. of Augsburg, Augsburg (Germany). Experimental Physics V, Center for Electronic Correlations and Magnetism; Academy of Sciences of Moldova, Chisinau (Republic of Moldova). Inst. of Applied Physics
  3. Univ. of Augsburg, Augsburg (Germany). Experimental Physics V, Center for Electronic Correlations and Magnetism
  4. Univ. of Warwick, Coventry (United Kingdom). Dept. of Physics
  5. Univ. Grenoble Alpes, Grenoble (France)
  6. Inst. Laue-Langevin (ILL), Grenoble (France)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Neutron Scattering Division
  8. Paul Scherrer Inst. (PSI), Villigen (Switzerland). Swiss Light Source
  9. Science and Technology Facilities Council (STFC), Harwell Campus, Oxford (United Kingdom). Diamond Light Source, Ltd.
  10. European Synchrotron Radiation Facility (ESRF), Grenoble (France). Swiss-Norwegian Beamlines
  11. Paul Scherrer Inst. (PSI), Villigen (Switzerland). Lab. for Neutron Scattering and Imaging; Univ. of Geneva (Switzerland). Dept. of Quantum Matter Physics
  12. Univ. of North Florida, Jacksonville, FL (United States). Dept. of Physics
  13. Paul Scherrer Inst. (PSI), Villigen (Switzerland). Lab. for Neutron Scattering and Imaging
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 97; Journal Issue: 13; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1468011
Alternate Identifier(s):
OSTI ID: 1434980

Gao, S., Guratinder, Kaur, Stuhr, Uwe, White, Jonathon S., Mansson, M., Roessli, Bertrand, Fennell, Tom, Tsurkan, V., Loidl, Alois, Hatnean, Monica Ciomaga, Balakrishnan, Geetha, Raymond, S, Chapon, L.C., Garlea, Vasile O., Savici, Andrei T., Cervellino, A., Bombardi, A., Chernyshov, D., Ruegg, Ch., Haraldsen, J. T., and Zaharko, Oksana. Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2O4. United States: N. p., Web. doi:10.1103/PhysRevB.97.134430.
Gao, S., Guratinder, Kaur, Stuhr, Uwe, White, Jonathon S., Mansson, M., Roessli, Bertrand, Fennell, Tom, Tsurkan, V., Loidl, Alois, Hatnean, Monica Ciomaga, Balakrishnan, Geetha, Raymond, S, Chapon, L.C., Garlea, Vasile O., Savici, Andrei T., Cervellino, A., Bombardi, A., Chernyshov, D., Ruegg, Ch., Haraldsen, J. T., & Zaharko, Oksana. Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2O4. United States. doi:10.1103/PhysRevB.97.134430.
Gao, S., Guratinder, Kaur, Stuhr, Uwe, White, Jonathon S., Mansson, M., Roessli, Bertrand, Fennell, Tom, Tsurkan, V., Loidl, Alois, Hatnean, Monica Ciomaga, Balakrishnan, Geetha, Raymond, S, Chapon, L.C., Garlea, Vasile O., Savici, Andrei T., Cervellino, A., Bombardi, A., Chernyshov, D., Ruegg, Ch., Haraldsen, J. T., and Zaharko, Oksana. 2018. "Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2O4". United States. doi:10.1103/PhysRevB.97.134430.
@article{osti_1468011,
title = {Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2O4},
author = {Gao, S. and Guratinder, Kaur and Stuhr, Uwe and White, Jonathon S. and Mansson, M. and Roessli, Bertrand and Fennell, Tom and Tsurkan, V. and Loidl, Alois and Hatnean, Monica Ciomaga and Balakrishnan, Geetha and Raymond, S and Chapon, L.C. and Garlea, Vasile O. and Savici, Andrei T. and Cervellino, A. and Bombardi, A. and Chernyshov, D. and Ruegg, Ch. and Haraldsen, J. T. and Zaharko, Oksana},
abstractNote = {In spinels ACr2O4(A=Mg,Zn), realization of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition at TN=12.5 K. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberg et al. [Pow. Diff. 17, 230 (2002)], while other features depend on sample or cooling protocol. A complex, partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectors k1=($\frac{1}{2}$ $\frac{1}{2}$ 0),k2=(1 0 $\frac{1}{2}$) appear. The ordered moment reaches 1.94(3) μB/Cr3+ for k1 and 2.08(3) μB/Cr3+ for k2, if equal amount of the k1 and k2 phases is assumed. The magnetic arrangements have the dominant components along the [110] and [1-10] diagonals and a smaller c component. We use inelastic neutron scattering to investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. Finally, the distinctive fingerprint of clusterlike excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.},
doi = {10.1103/PhysRevB.97.134430},
journal = {Physical Review B},
number = 13,
volume = 97,
place = {United States},
year = {2018},
month = {4}
}