Room temperature ferromagnetism in laser ablated transition-metal-doped TiO2 thin films on various types of substrates

Abstract

Under appropriate growth conditions, transition-metal-doped TiO2 (V/Cr/Fe/Co/Ni : TiO2) thin films deposited on various types of substrates by laser ablation could be ferromagnetic above room temperature. As for LaAlO3 substrates, which seem to be the best, when the growth temperature was 650°C, Fe/Co/Ni-doped TiO2 films could achieve a magnetic moment one order larger than that of films grown at 700°C, in the range of 1.5–2.9µB per impurity atom. These values are the largest for iron-group-doped-TiO2 that have been obtained so far. More interestingly, V/Cr-doped TiO2 films grown at both 650°C and 700°C could also have a large magnetic moment; however, growing at 650°C gives rise to a much larger one. Among all the transition-doped TiO2 thin films, the largest magnetic moment obtained is 4.3µB/V for V : TiO2 films grown at 650°C. Besides the convincing data from x-ray diffraction and magnetization, magnetic force microscopy measurements strongly suggest that the room temperature ferromagnetism in our films does not stem from any kind of dopant clusters. These genuine room temperature ferromagnets with very large magnetic moments appear to be very promising for applications.