Fe doping enhances ferromagnetism in MgTiO3 films

Abstract

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 A and the lattice constant c increases from 13.8882 to 13.9108 A 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 (EOBG) of the samples. EOBG = (4.55 − 2.67*x) eV demonstrates the relationship between EOBG 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.