Magnetoresistance of an all-manganite spin valve:: A thin antiferromagnetic insulator sandwiched between two ferromagnetic metallic electrodes

We study the magnetic and transport properties of an all-manganite spin valve consisting of a thin antiferromagnetic and insulating manganite sandwiched between two ferromagnetic and metallic manganite electrodes. When the ferromagnetic electrodes are in a parallel configuration, the double-exchange mechanism in the middle manganite slab is enhanced and the whole heterostructure becomes metallic. In the antiparallel alignment of the electrodes, the antiferromagnetic order in the middle layer is more robust and the resistance of the heterostructure is larger than in the parallel configuration. The strong dependence of the electronic structure of the middle manganite on the relative orientation of the magnetization in the leads turns out in a large tunneling magnetoresistance. We also find that the application of a magnetic field to the heterostructure in the parallel metallic configuration increases the electrical conductance, producing a large magnetoresistance. We discuss our conclusions in the context of recent experiments performed in manganite heterostructures.