Probing defect driven tunable spontaneous magnetization in paramagnetic Zn0.95Co0.05O epitaxial films by X-ray absorption investigations

In order to address existing unresolved issues related to intrinsic and extrinsic origins of ferromagnetism in Zn1_xCoxO based diluted magnetic semiconductors for varying x, the present work aims to investigate the tunable ferromagnetism triggered in paramagnetic Zn0.95Co0.05O films using 500 KeV inert xenon ion irradiation of different fluences. The origin of ferromagnetism in post irradiated Zn0.95Co0.05O films is understood from different densities of bound magnetic polarons (BMPs) formation through correlated spins of tetrahedrally substituted Co2þ ions and anionic vacancies. The alteration in crystallographic positions of Zn, Co cations, and O anions in the tetrahedral environment as analyzed from Zn and Co K-edgeX-ray absorption and O 1s photoemission is a crucial factor for the stabilization of different density of BMPs. Magnetic field and temperature dependence of X-ray magnetic circular dichroism at the Co L2,3 edge provide experimental evidence of purely paramagnetic contribution from well localized Co2þ ions of Co sublattice for paramagnetic Zn0.95Co0.05O film. The paramagnetic Co2þ ions of Co sublattice persist in irradiated films, which reveal BMPs formation as the origin of ferromagnetism.