Abstract
Local M–H loops have been measured on the free layer of a magnetic tunnel junction multilayers using the magneto-optical Kerr effect system, with 2 μm spatial resolution. The relatively irregular variations of coercivity H C (∼17.5 Oe) and exchange coupling field H E (∼7.5 Oe) are revealed in as-deposited sample prepared by the DC magnetron sputtering. After 200°C annealing, H C decreases to 15 Oe, while H E increases to 20 Oe with smooth local variation. Two-dimensional plots of H C and H E show the symmetric saddle shapes with their axes aligned with the pinned layer, where both H C and H E variations along free-layer axis are larger than those along pinned-layer axis. The increasing slope per micrometer of normalized H C and H E are the same near the junction edge along free-layer direction irrespective of junction size, giving the relatively uniform H C and H E for wider junction size.
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