Low-field colossal magnetoresistance in manganite tunnel spin valves

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Abstract
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)3O7, 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.