Improved tunneling magnetoresistance in interface engineered (La,Sr)MnO3 junctions

Spin tunnel junctions were fabricated and characterized with various insulating barriers and interface structures employing (La,Sr)MnO(3) (LSMO) as the ferromagnetic electrodes. Junctions with LaAlO(3) barriers exhibited systematically larger tunnel magnetoresistance (TMR) (TMR ratio similar to 230% at 10 K) than those with SrTiO(3) barriers (similar to 50%). When two unit cells of nondoped LaMnO(3) are inserted between LSMO and SrTiO(3) at both interfaces in the SrTiO(3)-barrier junction, the TMR was also significantly enhanced to similar 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 SrTiO(3)-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. (c) 2006 American Institute of Physics.