Sodium vanadium oxide Na2V6O16·3H2O nanobelts and nanorings: A new room-temperature ferromagnetic semiconductor

Abstract

We report the first observation of nanorings coiled by nanobelts in our synthesized Na₂V₆O₁₆·3H₂O (Barnesite) sample by a simple and novel cost-effective low-temperature hydrothermal method, and also find room temperature ferromagnetism in the product for the first time. The Na₂V₆O₁₆·3H₂O samples are characterized by XRD, SEM and XPS to ascertain their structure, morphology and composition. They exhibit ferromagnetic properties with coercivity of 400 Oe at 300 K observed from a hysteresis loop. The XPS spectra, and the hysteresis loops of the sample before and after annealing both demonstrate that the origin of ferromagnetism in the Na₂V₆O₁₆·3H₂O product is attributed to the introduction of oxygen vacancies. The polarization-induced self-coiling of in situ formed Na₂V₆O₁₆·3H₂O nanobelts is responsible for the formation of the perfectly circular nanoring geometry and it may be useful to investigate polar surface-induced growth processes, fundamental physics phenomena, and the design for nanoscale devices.