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Hydration-Induced Spin-Glass State in a Frustrated Na-Mn-O Triangular Lattice



Ioanna Bakaimi, Rosaria Brescia, Craig Brown, Alexander A. Tsirlin, Mark A. Green, Alexandros Lappas


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 analogues of the magnetic frustrated, mixed-valent manganese oxide structures, with general formula, NaxMnO2. Here we demonstrate that the direct hydration of layered rock-salt type α-NaMnO2, with the geometrically frustrated triangular lattice topology, yields the birnessite type oxide, Na0.36MnO2&#82260.2H2O, transforming its magnetic properties. This compound has a much-expanded interlayer spacing compared to its parent αNaMnO2 possess a Neel temperature of 45 K as a result of broken symmetry in the Mn3+ sub-lattice, the hydrated derivative undergoes a collective spin-freezing at 29 K within the Mn3+/Mn4+ sub-lattice. Scaling-law analysis of the frequency dispersion of the AC susceptibility and memory effects in the temperature dependent DC magnetization dependent DC magnetization confirm a cooperative spin-glass state of strongly interacting spins. This is supported by complementary spectroscopic analysis (HAADF-STEM, EELS) as well as structural analysis (high-resolution TEM, X-ray and neutron powder diffraction) that yield insights into the chemical and atomic structure modifications that mediate the spin-glass state. We conclude that the degree of spin-frustration in birnessite imposed by the underlinded triangular lattice topology is further enhanced by the in-plane bond-disorder generated by the mixed-valent character of manganese in the layers.
Physical Review B


magnetism, structure, spin glass, neutron diffraction


Bakaimi, I. , Brescia, R. , Brown, C. , Tsirlin, A. , Green, M. and Lappas, A. (2016), Hydration-Induced Spin-Glass State in a Frustrated Na-Mn-O Triangular Lattice, Physical Review B, [online], (Accessed July 15, 2024)


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Created May 17, 2016, Updated October 12, 2021