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Synthesis and characterization of Na03RhO206H2O - a semiconductor with a weak ferromagnetic component

S. Park·K. Kang·W. Si·W. -S. Yoon·Y. Lee·A. R. Moodenbaugh·L. H. Lewis·T. Vogt
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Abstract

We have prepared the oxyhydrate Na03RhO206H2O by extracting Na+ cations from NaRhO2 and intercalating water molecules using an aqueous solution of Na2S2O8. Synchrotron X-ray powder diffraction, thermogravimetric analysis (TGA), and energy-dispersive x-ray analysis (EDX) reveal that a non-stoichiometric Na03(H2O)06 network separates layers of edge-sharing RhO6 octahedra containing Rh3+(4d6, S=0) and Rh4+ (4d5, S=1/2). The resistivities of NaRhO2 and Na03RhO206H2O (T < 300) reveal insulating and semi-conducting behavior with activation gaps of 134 meV and 7.8 meV, respectively. Both Na03RhO206H2O and NaRhO2 show paramagnetism at room temperature, however, the sodium-deficient sample exhibits simultaneously a weak but experimentally reproducible ferromagnetic component. Both samples exhibit a temperature-independent Pauli paramagnetism, for NaRhO2 at T > 50 K and for Na03RhO206H2O at T > 25 K. The relative magnitudes of the temperature-independent magnetic susceptibilities, that of the oxide sample being half that of the oxyhydrate, is consistent with a higher density of thermally accessible electron states at the Fermi level in the hydrated sample. At low temperatures the magnetic moments rise sharply, providing evidence of localized and weakl -ordered electronic spins.

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S. Park, K. Kang, W. Si, W. -S. Yoon, Y. Lee, A. R. Moodenbaugh, L. H. Lewis, T. Vogt. 2005-03-31. Synthesis and characterization of Na03RhO206H2O - a semiconductor with a weak ferromagnetic component. https://doi.org/10.1016/j.ssc.2005.03.063

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