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Quantum Beam Sci. 2018, 2(3), 16; https://doi.org/10.3390/qubs2030016

The Magnetic Phase Transition and Universality Class of h-YMnO3 and h-(Y0.98Eu0.02)MnO3 Under Zero and Applied Pressure

1
Nanoscience Center, Niels Bohr Institute, University of Copenhagen, 2100 Copenhagen, Denmark
2
Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
3
Institut für Theoretische Physik, Universität Leipzig, 04103 Leipzig, Germany
4
Laboratory for Multiscale Materials Experiments, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
*
Author to whom correspondence should be addressed.
Received: 30 June 2018 / Revised: 21 August 2018 / Accepted: 27 August 2018 / Published: 31 August 2018
(This article belongs to the Special Issue Magnetic Materials and Magnetism)
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Abstract

We investigated the antiferromagnetic phase transition in the frustrated and multiferroic hexagonal manganites h-YMnO 3 (YMO) and h-(Y 0.98 Eu 0.02 )MnO 3 (YEMO). Elastic neutron scattering was used to study, in detail, the phase transition in YMO and YEMO under zero pressure and in YMO under a hydrostatic pressure of 1.5 GPa. Under conditions of zero pressure, we found critical temperatures of T N = 71.3 ( 1 ) K and 72.11 ( 5 ) K and the critical exponent 0.22 ( 2 ) and β = 0.206 ( 3 ) , for YMO and YEMO, respectively. This is in agreement with earlier work by Roessli et al. Under an applied hydrostatic pressure of 1.5 GPa, the ordering temperature increased to T N = 75.2 ( 5 ) K, in agreement with earlier reports, while β was unchanged. Inelastic neutron scattering was used to determine the size of the anisotropy spin wave gap close to the phase transition. From spin wave theory, the gap is expected to close with a critical exponent, β , identical to the order parameter β . Our results indicate that the gap in YEMO indeed closes at T N = 72.4 ( 3 ) K with β = 0.24 ( 2 ) , while the in-pressure gap in YMO closes at 75.2(5) K with an exponent of β = 0.19 ( 3 ) . In addition, the low temperature anisotropy gap was found to have a slightly higher absolute value under pressure. The consistent values obtained for β in the two systems support the likelihood of a new universality class for triangular, frustrated antiferromagnets. View Full-Text
Keywords: critical exponent; multiferroics; spin-wave; magnetic phase transition; applied pressure; inelastic neutron scattering critical exponent; multiferroics; spin-wave; magnetic phase transition; applied pressure; inelastic neutron scattering
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Holm-Dahlin, S.; Janas, S.; Kreisel, A.; Pomjakushina, E.; White, J.S.; Fennell, A.L.; Lefmann, K. The Magnetic Phase Transition and Universality Class of h-YMnO3 and h-(Y0.98Eu0.02)MnO3 Under Zero and Applied Pressure. Quantum Beam Sci. 2018, 2, 16.

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