Electronic transport in oxygen deficient ferromagnetic semiconducting TiO2-delta

TiO2−δ films were deposited on (100) lanthanum aluminate, LaAlO3, substrates at a low oxygen chamber pressure, P ≈ 0.3 mTorr, employing a pulsed laser ablation deposition technique. In previous work, it was established that the oxygen deficiency in these films induced ferromagnetism. In this work it is demonstrated that this same oxygen deficiency also gives rise to semiconductor titanium ion impurity donor energy levels. Measurements of the transport resistivity of thin films of TiO2−δ are presented, as a function of temperature and magnetic field. The magnetoresistivity and Hall resistivity are explained in terms of electronic excitations from the titanium ion donor levels into the conduction band. (Some figures in this article are in colour only in the electronic version)