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Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet α−Li2IrO3.

Choi, Sungkyun and Manni, S. and Singleton, J. and Topping, C. V. and Lancaster, T. and Blundell, S. J. and Adroja, D. T. and Zapf, V. and Gegenwart, P. and Coldea, R. (2019) 'Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet α−Li2IrO3.', Physical review B, 99 (5). 054426.


The layered honeycomb iridate α-Li2IrO3 displays an incommensurate magnetic structure with counterrotating moments on nearest-neighbor sites, proposed to be stabilized by strongly frustrated anisotropic Kitaev interactions between spin-orbit entangled Ir4+ magnetic moments. Here we report powder inelastic neutron scattering measurements that observe sharply dispersive low-energy magnetic excitations centered at the magnetic ordering wave vector, attributed to Goldstone excitations of the incommensurate order, as well as an additional intense mode above a gap 2.3 meV. Zero-field muon-spin relaxation measurements show clear oscillations in the muon polarization below the Néel temperature TN 15 K with a time-dependent profile consistent with bulk incommensurate long-range magnetism. Pulsed-field magnetization measurements observe that only about half the saturation magnetization value is reached at the maximum field of 64 T. A clear anomaly near 25 T indicates a transition to a phase with reduced susceptibility. The transition field has a Zeeman energy comparable to the zero-field gapped mode, suggesting gap suppression as a possible mechanism for the field-induced transition.

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Publisher statement:Reprinted with permission from the American Physical Society: Choi, Sungkyun, Manni, S., Singleton, J., Topping, C. V., Lancaster, T., Blundell, S. J., Adroja, D. T., Zapf, V., Gegenwart, P. & Coldea, R. (2019). Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet α−Li2IrO3. Physical Review B 99(5): 054426 © 2019 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.
Date accepted:23 January 2019
Date deposited:08 March 2019
Date of first online publication:25 February 2019
Date first made open access:08 March 2019

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