By measuring the extraordinary Hall effect on a series of naturally oxidized Pt3 nm/Co90Fe10 0.6 nm/Al tAl samples with 0<tAl<1.2 nm, a first crossover from in-plane to perpendicular magnetic anisotropy is observed when tAl is varied from 0 to 0.2 nm. The CoFe magnetization remains out of plane for 0.2<tAl<0.5 nm. When the Al thickness is further increased, a second crossover back to in plane takes place. In a series of samples in which the Al thickness is kept constant, the same behavior is observed as the time of exposure to an oxygen plasma is varied. The results clearly indicate that the degree of oxidation of Al at the CoFe/AlOx interface has a dramatic effect on the magnetic anisotropy of the transition-metal layer. These sharp crossovers of anisotropy provide a very accurate and convenient way to monitor the oxidation of the tunnel barrier in magnetic tunnel junctions. This technique is also applied to characterize the oxidation kinetics of various ultrathin metallic layers as well as the aging effect in alumina barriers.

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Small magnetic domains ͑70 nm͒ have been observed by magnetic force microscopy in ordered FePd thin films grown by molecular-beam epitaxy. The layers exhibit a perpendicular magnetic anisotropy induced by uniaxial L1 0 ͓CuAu͑I͒-type͔ chemical ordering. The magnetization curves show that the easy magnetization axis is perpendicular to the film plane and their interpretation with a micromagnetic model leads to the correct size of the domains.