Magnetoresistance and dipole shift of ultrasmall magnetic tunnel junctions characterized by conducting atomic force microscopy

Conducting atomic force microscopy was used for the characterization of magnetic tunnel junctions with various areas down to a minimum of 0.0025 mum(2) and a tunnel magnetoresistance (TMR) value up to 20%. Minor loops of large junctions show jumps, of the resistance, which can be related to magnetic domains formation in the ferromagnetic electrodes. For the smallest junctions, a TMR signal between 10% and 17% was obtained. The range of TMR values increased with decreasing junction,sizes. The minor loops of such small junctions did not show hints of domains. We observed, however, a shift of the minor loop in the opposite direction as obtained for larger junctions, which can be related to dipolar antiferromagnetic coupling of the ferromagnetic electrodes.