Fe doping enhances ferromagnetism in MgTiO₃ films

MgTiO₃ films with different Fe concentrations were grown on silicon wafers using chemical solutions. These films have hexagonal structures with R-3 space groups as measured via X-ray diffraction analysis. The lattice constant a increases from 5.0508 to 5.0577 Å and the lattice constant c increases from 13.8882 to 13.9108 Å as the Fe concentration increases from 0.00 to 0.07. The handled ellipsometric spectra with Tauc–Lorentz dielectric model, in a 240 and 825 nm wavelength range, was produced to analyze the optical dispersion of the films. At a 532 nm wavelength, the refractive index n of the samples first is increased and then decreased due to Fe doping. Fe doping narrowed the optical band gap (E_OBG) of the samples. E_OBG = (4.55 − 2.67*x) eV demonstrates the relationship between E_OBG and Fe content x. The undoped MgTiO₃ film presents a very weak ferromagnetic order from the oxygen vacancies, and the x = 0.01 Fe-doped film shows apparent ferromagnetism. As the iron concentration x > 0.01, the unsaturated magnetization characteristic of the samples is displayed. These results suggest a complex magnetic behavior of Fe-doped MgTiO₃ films, which is related to the coexistence and competition of ferromagnetism from Fe³⁺–Vo–Fe³⁺ exchange and bound magnetic polarons and antiferromagnetism from two Fe³⁺ ions.