Magnetic tunnel sensors with Co-Cu artificial antiferromagnetic (AAF) hard subsystem

Micron-size magnetic tunnel junctions are studied, in which the pinning of the hard magnetic reference layer is accomplished by the so-called Artificial Antiferromagnetic Subsystem (AAF). In the AAF, two Co layers are antiferromagnetically coupled by a 1 nm thick Cu layer, thus giving rise to stability windows larger than 2 kA/m for the AAF. Al/sub 2/O/sub 3/-tunnel barriers of 1 and 1.5 nm Al thickness were put on top of the AAF and at its opposite surface Fe detection layers are located. The signal could be enhanced by a factor of two to 22% by inserting a 1 nm Co-coating between the barrier and the Fe. Thus sensors were realized with signals four times higher than for the GMR counterparts.