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arXiv · 1810.03212

Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet ${\alpha}$-Li$_2$IrO$_3$

Sungkyun Choi·S. Manni·J. Singleton·C. V. Topping·T. Lancaster·S. J. Blundell·D. T. Adroja·V. Zapf·P. Gegenwart·R. Coldea
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Abstract

The layered honeycomb iridate $\alpha$-Li$_2$IrO$_3$ 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 Ir$^{4+}$ magnetic moments. Here we report powder inelastic neutron scattering measurements that observe sharply dispersive low-energy magnetic excitations centered at the magnetic ordering wavevector, attributed to Goldstone excitations of the incommensurate order, as well as an additional intense mode above a gap $\Delta\simeq2.3$ meV. Zero-field muon-spin relaxation measurements show clear oscillations in the muon polarization below the N\'{e}el temperature $T_{\rm N}\simeq15$ 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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Sungkyun Choi, S. Manni, J. Singleton, C. V. Topping, T. Lancaster, S. J. Blundell, D. T. Adroja, V. Zapf, P. Gegenwart, R. Coldea. 2018-10-07. Spin dynamics and field-induced magnetic phase transition in the honeycomb Kitaev magnet ${\alpha}$-Li$_2$IrO$_3$. https://doi.org/10.1103/physrevb.99.054426

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