Abstract

The Mn³⁺-containing oxide MnTaO₄ was synthesized at 1050 °C and 2 kbar partial oxygen gas pressure. It has a rutile-type structure, space group P4₂/mnm, with a = 4.7189(3), c = 2.9843(3) Å, and a statistical distribution of Mn/Ta. The structure was refined by the Rietveld method using both X-ray and neutron powder diffraction. The refinements, and energy-dispersive X-ray microanalysis, indicate that the phase may contain a small amount of Mn⁴⁺ and have the actual composition Mn_1.08(2)Ta_0.92(2)O₄. The magnetic susceptibility shows a maximum at 16 K and Curie–Weiss behavior at higher temperatures, with μ_eff = 5.11(4) μ_B per Mn atom. The susceptibility is consistent with spin-glass behavior: (i) the temperature at the susceptibility maximum is frequency-dependent and (ii) field cooled and zero-field cooled susceptibility curves differ below the maximum. Neutron powder diffraction data collected at 10 K does not show any sharp magnetic reflections, but a very broad reflection, with a full width at half maximum height of 7°, at a position corresponding to the 100 reflection is seen.