Oxygen Vacancy Driven Room Temperature Ferromagnetism in Biogenic Synthesized Black Zirconia Nanoparticles

We herein report the emergence of ferromagnetic ordering in black zirconia nanoparticles at room temperature, induced by the oxygen vacancies present in the sample. Black zirconia nanoparticles were synthesized in a biogenic route employing Melia Dubia extract and the prepared nanoparticles are observed to have crystallized in the metastable cubic phase. The optical absorption characteristics shows extended absorption in the ultraviolet and visible region, which is consistent with the black hue of the sample. The morphological analysis reveals that the shape is roughly spherical, with particle size between 200 and 250 nm. Electron paramagnetic resonance (EPR) spectrum offers insights into the origin of magnetism stemming from the presence of singly charged oxygen vacancies. The magnetization (M–H) hysteresis loop exhibits a clear signature of ferromagnetism (M_s = 23.12 memu g⁻¹, H_c = 13.17 mT) at room temperature arising from double exchange mediated ferromagnetic coupling between localized paramagnetic centers and itinerant electrons in the conduction band. The progress in oxygen vacancy-driven magnetism at room temperature marks a substantial advancement in integrating spin functionality into non-magnetic semiconductors through defect states.