d⁰ Ferromagnetism in Oxide Nanowires: Role of Intrinsic Defects

Department of Condensed Matter Physics and Material Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake City, Kolkata 700 098, India.

Abstract

In this report, we have investigated the origin of defect-induced room-temperature d⁰ ferromagnetism in pure SnO₂ and ZnO nanowires (NWs) with average diameter ~ 50 nm, prepared by template assisted route. Photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopic measurements show the singly ionized oxygen vacancy is inducing ferromagnetism in pure SnO₂ NWs whereas cation (Zn) vacancy is found to responsible for the ferromagnetic behaviour in pure ZnO NWs. Besides, it is found that the Zn vacancy-induced ferromagnetism in ZnO can be tuned by substituting few percentage of nonmagnetic alkali metal like potassium (K) at Zn site. Saturation moment as well as Curie temperature has found to increase significantly with K-doping up to 4 at.% but a decrease of ferromagnetic response is observed for higher K-doping. X-ray photoelectron spectra show that K⁺¹ ions substitute at Zn site and thus introduce hole through which a ferromagnetic interaction between Zn vacancies can be mediated. The direct correlation between the Zn vacancy concentration and the corresponding saturation moment indicates that Zn vacancyinduced ferromagnetism in ZnO can be successfully tuned by K-doping that can an exciting approach to prepare ZnO-based dilute magnetic semiconductors for modern spintronic technology.