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

We have studied the magnetic and electrical properties of LaySr1-yTi0.9Fe0.1O3-delta 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 mu(B)/Fe to 0.2 mu(B)/Fe. The SrTi0.9Fe0.1O3-delta (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-delta 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. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3525707]