Electronic Transport in the Oxygen Deficient Ferromagnetic Semiconducting TiO${}_{2-\delta }$

TiO${}_{2-\delta }$ films were deposited on (100) Lanthanum aluminates LaAlO${}_3$ substrates at a very low oxygen chamber pressure $P\approx 0.3$ 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. Transport resistivity measurements in thin films of TiO${}_{2-\delta }$ are presented as a function of temperature and magnetic field. Magneto- and Hall- resistivity is explained in terms of electronic excitations from the titanium ion donor levels into the conduction band.