Negative spin polarization in (La,Sr)CoO3 probed by a magnetic tunnel junction with (La,Sr)MnO3

By using perovskite (La,Sr)MnO3 (LSMO)-based magnetic tunnel junctions with LaAlO3 barrier, we have experimentally revealed the spin state of (La,Sr)CoO3 (LSCO) that was employed as the counterelectrode of the junctions. Inverse tunnel magnetoresistance (TMR) up to −14% was observed at 10K in low-bias measurement. This indicates that t2g↓ electrons are the majority at the Fermi level in the LSCO band structure, taking into account the half-metallic character of LSMO. The temperature dependence of the interfacial spin polarization of LSCO as deduced from the TMR ratio indicates the reduction of the Curie temperature at the interface by 70K. The TMR ratio exhibits an asymmetric bias dependence in qualitative agreement with the calculated spin band structure of LSCO.

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