Origin of magnetism in La and Fe doped SrTiO3−δ films

We have studied the magnetic and electrical properties of LaySr1−yTi0.9Fe0.1O3−δ films for compositions where y=0, 0.2, 0.5, and 0.7. All the films exhibited room temperature ferromagnetism with a magnetic moment ranging from 0.7 μB/Fe to 0.2 μB/Fe. The SrTi0.9Fe0.1O3−δ (y=0) sample is an insulator with a small polaron like temperature dependence of resistivity. On the other hand y=0.2 and y=0.5 films exhibited a metallic type of resistivity which can be described by a power law. The largest magnetic moment was observed in the most resistive member (y=0) of the LaySr1−yTi0.9Fe0.1O3−δ family. This is in contrast to the carrier mediated magnetism models. The origin of the magnetism in highly resistive y=0 film could be attributed to the mixed valence state of Fe. On the other hand, La doped sample (y>0) exhibited features of carrier mediated magnetism as well as the mixed valence magnetism. The origin of the observed magnetism in all films has been discussed.