Enhancing the Magnetic Moment of Ferrimagnetic NiCo2O4 via Ion Irradiation driven Oxygen Vacancies

Ion irradiation has emerged as a powerful tool for the efficient control of uniaxial lattice expansion to fine tune and modulate the otherwise inaccessible complex correlated phases in oxide thin-films. We report the fine tuning of the magnetic moment, ferromagneticparamagnetic and metal-insulator transition temperatures in the NiCo2O4 inverse-spinel oxide by creating oxygen deficiencies, employing high energy He-ion irradiation. Tailoring of oxygen vacancies and consequently a uniaxial lattice expansion in the out-of-plane direction drives the system towards the increase of the magnetic moment by two-times in magnitude.
The magnetic moment increases with the He-ion irradiation fluence up to 2.5×1016/cm2 . Our results are corroborated well by spin-polarized electronic structure calculations with density functional theory and X-ray absorption spectroscopic data which show peak-height change and energy shift of Co-L2,3 and Ni-L2,3 edges driven by the oxygen vacancies. These results demonstrate a new pathway of tailoring oxygen vacancies via He-ion irradiation, useful for designing new functionalities in other complex oxide thin-films.