Improved Room-Temperature Ferromagnetism in Nd-Doped SnO₂ Nanostructures through Defect Engineering

Abstract

Many efforts have been made to introduce room-temperature ferromagnetism (RTFM) in metal oxide semiconductors doped with either magnetic or nonmagnetic ions for their suitable application in spintronics in the past few years. However, it is not yet well understood whether the origin of RTFM in these systems is intrinsic or because of magnetic clusters. Hence, we report detailed experimental investigations on RTFM in Nd-doped SnO2 nanostructures synthesized using a sol–gel process, which has potential spintronics application. In the present work, we observe that defects/oxygen vacancies play a crucial role in improving the RTFM in SnO2 doped with Nd ions. The presence of oxygen vacancies in the prepared samples was confirmed by Raman scattering, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The enhancement of the density of oxygen vacancies was further quantified by the deconvoluted core-level O 1s XPS spectra. All samples exhibited RTFM with a small contribution of paramagnetic (PM) ordering. These phases (FM + PM) were established by fitting all M–H curves using a two-phase theoretical model. Furthermore, the Curie–Weiss and spin wave (CWSW) model fitted the M–T curve well, which also indicated the existence of the two phases in our systems. The overlapping of bound magnetic polarons occurred because of the exchange interaction between Nd3+ ions and electrons trapped in oxygen vacancies; this overlap is responsible for introducing RTFM in Nd-doped SnO2. Hence, the origin of RTFM can be mostly explained by the bound magnetic polaron (BMP) model.