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Hydration-induced spin-glass state in a frustrated Na-Mn-O triangular lattice

Bakaimi, Ioanna, Brescia, Rosaria, Brown, Craig M., Tsirlin, Alexander A., Green, M.A., Lappas, Alexandros (2016) Hydration-induced spin-glass state in a frustrated Na-Mn-O triangular lattice. Physical Review B, 93 (18). Article Number 184422. ISSN 2469-9950. (doi:10.1103/PhysRevB.93.184422) (KAR id:60105)

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Birnessite compounds are stable across a wide range of compositions that produces a remarkable diversity in their physical, electrochemical, and functional properties. These are hydrated analogs of the magnetically frustrated, mixed-valent manganese oxide structures, with general formula, NaxMnO2. Here we demonstrate that the direct hydration of layered rock-salt type ?-NaMnO2, with the geometrically frustrated triangular lattice topology, yields the birnessite type oxide, Na0.36MnO2?0.2H2O, transforming its magnetic properties. This compound has a much-expanded interlayer spacing compared to its parent ?-NaMnO2 compound. We show that while the parent ?-NaMnO2 possesses a Néel temperature of 45 K as a result of broken symmetry in the Mn3+ sublattice, the hydrated derivative undergoes collective spin freezing at 29 K within the Mn3+/Mn4+ sublattice. Scaling-law analysis of the frequency dispersion of the ac susceptibility, as well as the temperature-dependent, low-field dc magnetization confirm a cooperative spin-glass state of strongly interacting spins. This is supported by complementary spectroscopic analysis [high-angle annular dark-field scanning transmission electron miscroscopy (TEM), energy-dispersive x-ray spectroscopy, and electron energy-loss spectroscopy] as well as by a structural investigation (high-resolution TEM, x-ray, and neutron powder diffraction) that yield insights into the chemical and atomic structure modifications. We conclude that the spin-glass state in birnessite is driven by the spin frustration imposed by the underlying triangular lattice topology that is further enhanced by the in-plane bond-disorder generated by the mixed-valent character of manganese in the layers.

Item Type: Article
DOI/Identification number: 10.1103/PhysRevB.93.184422
Divisions: Divisions > Division of Natural Sciences > Physics and Astronomy
Depositing User: Mark Green
Date Deposited: 26 Jan 2017 13:15 UTC
Last Modified: 09 Dec 2022 05:24 UTC
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