Abstract
Spin tunnel junctions were fabricated and characterized with various insulating barriers and interface structures employing (La,Sr)MnO3 (LSMO) as the ferromagnetic electrodes. Junctions with LaAlO3 barriers exhibited systematically larger tunnel magnetoresistance (TMR) (TMR ratio ∼230% at 10K) than those with SrTiO3 barriers (∼50%). When two unit cells of nondoped LaMnO3 are inserted between LSMO and SrTiO3 at both interfaces in the SrTiO3-barrier junction, the TMR was also significantly enhanced to ∼170%. These results, including the temperature dependence of TMR, qualitatively agree with the characteristics of the local magnetization at the interface that was evaluated by magnetization-induced second harmonic generation (MSHG) for the corresponding interface structures. However, slight deviations appear as a systematic suppression of TMR for all the junctions at high temperatures compared with MSHG results. Also, TMR results appear to be more degraded than MSHG results for the SrTiO3-barrier junctions. The barrier thickness dependence of the TMR response revealed that a spin-independent and inelastic conduction channel is a possible origin for the apparent suppression of TMR compared with MSHG.
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