Emergence of ferromagnetism in (Ti, Cr) co-doped SnO₂ nanoparticles

In this study, pure SnO₂, Ti-doped SnO₂, and (Ti–Cr) co-doped SnO₂ nanoparticles were successfully synthesized using a simple solid-state reaction method, with the Ti concentration kept constant at 1.5%. The prepared samples were analyzed using X-ray photoelectron spectroscopy (XPS) to investigate the chemical state of the elements and the availability of oxygen vacancies. The XPS study revealed oxidation state of + 4, + 4, and + 3 for Sn, Ti, and Cr, respectively. The magnetic properties were studied using a vibrating sample magnetometer. All samples displayed ferromagnetic properties at room temperature, except for the co-doped sample with a 5.5% Cr doping concentration. Pure SnO₂ nanoparticles exhibited room-temperature ferromagnetism (RTFM) with a saturation magnetization of 5.24 memu/g. Ti-doped SnO₂ displayed RTFM with a high saturation magnetization of 8.49 memu/g. The co-doped sample, with 1.5% and 3.5% Cr doping concentration, demonstrated RTFM with respective saturation magnetization values of 6.39 memu/g and 5.03 memu/g. This behaviour is best explained by the concept of a bound magnetic polaron. The observed ferromagnetism can be attributed to the creation of oxygen vacancies, which were thoroughly examined using XPS. However, as the concentration of Cr dopant increased to 5.5%, the ferromagnetism converted to diamagnetism due to the Cr–O–Cr antiferromagnetic super-exchange interaction. These results establish that oxygen vacancies are crucial in determining the magnetic properties of these materials.