Magnetic distribution of the free layer on patterned MTJ multilayers

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 HC (∼17.5 Oe) and exchange coupling field HE (∼7.5 Oe) are revealed in as-deposited sample prepared by the DC magnetron sputtering. After 200°C annealing, HC decreases to 15 Oe, while HE increases to 20 Oe with smooth local variation. Two-dimensional plots of HC and HE show the symmetric saddle shapes with their axes aligned with the pinned layer, where both HC and HE variations along free-layer axis are larger than those along pinned-layer axis. The increasing slope per micrometer of normalized HC and HE are the same near the junction edge along free-layer direction irrespective of junction size, giving the relatively uniform HC and HE for wider junction size.