Giant magnetoresistance in Ni-Fe/Co/Al-AlOx/Co/Ni-Fe/Fe-Mn ferromagnetic tunnel junctions

To develop candidate magnetic sensors for the future generation of magnetic read heads, we have fabricated Ni-Fe/Co/Al-AlOx/Co/Ni-Fe/Fe-Mn/Ni-Fe ferromagnetic tunnel junctions with oxidized Al barriers. To form the barrier layer, the Al was oxidized in air or in oxygen plasma. These junctions showed changes in tunnel resistance (magneto-resistance ratio) of 10 to 15% upon the application of a magnetic field. Some of the junctions exhibited good thermal stability over 300 degrees C and the magneto-resistance (MR) ratios were increased by annealing. The largest MR ratio after annealing at 300 degrees C for one hour was 24%, which is much larger than that of spin-valve films. The junctions with naturally oxidized barriers and plasma-oxidized barriers had almost the same properties, but the plasma-oxidization process is much faster. Current research indicates that ferromagnetic tunnel junctions have good potential for use in magnetic read heads.