Low-field colossal magnetoresistance in manganite tunnel spin valves

We report on the magnetoresistive properties of all-oxide tunnel spin valves in which electrodes of mixed valence manganites (La0.7Sr0.3MnO3) are separated by a thin insulating layer. The structures were prepared by Pulsed Laser Deposition and several tunnel barriers were used including PrBa2(CuGa)(3)O-7, CeO2 and SrTiO3. The latter gives the largest magnetoresistive effect where the trilayer's resistance is increased by a factor of 5.5 at 50 Gauss and 4.2 K. Analysis of the temperature variation of the barrier resistivity shows that the dramatic loss of the magnetoresistive effect above 150 K is due to a reduced oxygen content of the interface between La0.7Sr0.3MnO3 and SrTiO3. Solving this problem should lead to similar results at room temperature.