Abstract
In spin valve and magnetic tunnel junction systems, the soft sensing layer should be sensitive to small fields of a few hundred A/m and should not be influenced by the adjacent magnetic hard layer. In polycrystalline films, however, congruent interface roughness invokes a ferromagnetic coupling, which can be compensated by an antiferromagnetic magnetostatic dipole coupling in patterned elements. In this paper, we demonstrate the evolution of the magnetic interlayer interaction by annealing in tunnel junctions with Al2O3 barrier. Whereas the minor loop shifting field of the soft magnetic NiFe sense layer is constant or varies only slightly from 2 kA/m to 1.15 kA/m for 1–1.5 nm thick barriers, an eightfold increase of the coercivity is found after annealing above 350 °C. Microstructural investigations give evidence that small ferromagnetic clusters arise in the hard layer of the junctions (Cu/CoFe/Ru/CoFe) by diffusion of Cu, Co, and Fe. The density and the stray field of these clusters are determined by magnetic force measurements and can be correlated to the increased switching field strength.
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