Study of NiFe/Al/Al2O3 magnetic tunnel junction interfaces using second-harmonic magneto-optic Kerr effect

Using the second-harmonic magneto-optic Kerr effect (SHMOKE), we have measured the interfacial magnetic properties of NiFe/Al/Al2O3 heterostructures as a function of Al2O3 thickness and processing conditions. The samples were prepared like magnetic tunnel junctions except that the top electrodes were not deposited. A large change in SHMOKE contrast was observed for different oxidation processes and Al2O3 thicknesses. The magnetic SHMOKE contrast from a plasma oxidized sample in which the oxidation front is thought to be inside the original NiFe film is 70%, whereas the SHMOKE contrast from a thermally oxidized NiFe/Al sample, in which the oxidation front is similar to 1 nm from the Al/NiFe interface is only 15%. Further, the phase of the signal is reversed between the two structures. The SHMOKE data have been correlated with tunneling measurements on similarly fabricated structures. For the two samples listed above, the junction resistivity varied from 10(-1) Omega cm(2) (plasma oxidized) to 10(-6) Omega cm(2) (thermally oxidized). These results indicate that SHMOKE may be useful for assessing tunnel junction quality during processing. [S0021-8979(99)49408-3].