In situ applied field imaging of a magnetic tunnel junction using magnetic force microscopy

Knowledge of domain behavior in magnetic tunnel junctions is an essential component, together with knowledge of the electron band structure, for understanding their magnetoelectronic properties. To this purpose, the magnetization reversal processes of a multilayertunnel junction of structure substrate/NiFe/AlOx/FeCo/CrPtMn/Al of tapered half-ellipsoid shape have been imaged using a magnetic force microscope(MFM) within situ applied magnetic fields. Stripe domains through both the stack and free layers observed at zero applied field were erased by a ∼100 Oe field applied to the left followed by applying a small field to the right. Magnetic domain structure did not reappear in the MFM images until a field of ∼400 Oe was applied to the right. This domain pattern then persisted when the magnetic field was reduced to zero. A drastic difference in domain patterns throughout the rotational processes to saturation in each direction was also observed. When the field was applied to the left, domain walls rotated toward the direction perpendicular to the applied field before disappearing. However, in near-saturation fields to the right, domain walls formed nearly parallel to the applied field and rotated away from parallel as the applied field strength was decreased. From these images, therefore, significant insight has been gained into the magnetization processes and physical phenomena behind the magnetoresistive behavior of these junctions