Ferromagnetic Properties of N-Doped and Undoped TiO₂ Rutile Single-Crystal Wafers with Addition of Tungsten Trioxide.

In this work, undoped, N-doped, WO₃-loaded undoped, and WO₃-loaded with N-doped TiO₂ rutile single-crystal wafers were fabricated by direct current (DC) magnetron sputtering. N-doping into TiO₂ and WO₃ loading onto TiO₂ surface were used to increase and decrease oxygen vacancies. Various measurements were conducted to analyze the structural and magnetic properties of the samples. X-ray diffraction results showed that the N-doping and WO₃ loading did not change the phase of all samples. X-ray photoelectron spectroscopy results revealed that W element loaded onto rutile single-crystal wafers existed in the form of WO₃. UV-Vis spectrometer results showed that the absorption edge of WO₃-loaded undoped and WO₃-loaded with N-doped TiO₂ rutile single-crystal wafers had red shift, resulting in a slight decrease in the corresponding band gap. Photoluminescence spectra indicated that oxygen vacancies existed in all samples due to the postannealing atmosphere, and oxygen vacancies density increased with N-doping, while decreasing with WO₃ loading onto TiO₂ surface. The magnetic properties of the samples were investigated, and the saturation magnetization values were in the order N-doped > WO₃-loaded with N-doped > undoped > WO₃-loaded undoped rutile single-crystal wafers, which was the same order as the oxygen vacancy densities of these samples. N-doping improved the saturation magnetization values, while WO₃-loaded decreased the saturation magnetization values. This paper reveals that the magnetic properties of WO₃-loaded with N-doped rutile single-crystal wafers originate from oxygen vacancies.