Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance,
and coercivity from 4.2 K to room temperature and applied voltage dependen
ce of the TMR ratio and resistance at room temperature for a tunnel junctio
n, Ta (5 nm)/Ni79Fe21 (3 nm)/Cu (20 nm)/Ni79Fe21 (3 nm)/Ir22Mn78 (10 nm)/Co
75Fe25 (4 nm)/Al (0.8 nm)-oxide/Co75Fe25 (4 nm)/Ni79Fe21 (20 nm)/Ta(5 nm),
were investigated. TMR ratio, effective barrier height and width, and break
down voltage of the junction can be remarkably enhanced after annealing at
300 degrees C for an hour. High TMR ratio of 49.7% at room temperature and
69.1% at 4.2 K were observed. The value of spin polarization of Co75Fe25, P
= 50.7%, deduced from the TMR ratio at 4.2 K was corresponding well to the
experimental data measured at 0.2 K in a spin polarized tunneling experime
nt using a superconductor/insulator/ferromagnet tunneling junction. (C) 200
0 American Institute of Physics. [S0003-6951(00)05028-2].