Magnetoresistance of spin-dependent tunnel junctions with composite electrodes

Spin-dependent tunnel junctions, Co/Al2O3/Co (CoFe)/NiFe, were fabricated to investigate the effect of the additional Co (CoFe) interlayer on tunneling magnetoresistance. The quality of the junction was examined with a cross-sectional image generated by high-resolution transmission electron microscopy, and an electron energy loss spectra map. For junctions with a Co (CoFe) interlayer in the top electrode thinner than 0.8 nm (1.0 nm), the tunneling magnetoresistance ratio increases with interlayer thickness. For junctions with a 0.8-2.0 nm Co (1.0-2.0 nm CoFe) interlayer in the top electrode, the tunneling magnetoresistance ratio reaches the maximum value of 2.16 (4.45) times that without any Co (CoFe) interlayer in the top electrode. The increase in the tunneling magnetoresistance ratio may be attributed to the increased effective ferromagnetic electrode polarization and the various spin-flip scattering factors. (C) 2001 American Institute of Physics.