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 measu red the interfacial magnetic properties of NiFe/Al/Al2O3 heterostructures a s a function of Al2O3 thickness and processing conditions. The samples were prepared like magnetic tunnel junctions except that the top electrodes wer e not deposited. A large change in SHMOKE contrast was observed for differe nt 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 t hermally oxidized NiFe/Al sample, in which the oxidation front is similar t o 1 nm from the Al/NiFe interface is only 15%. Further, the phase of the si gnal is reversed between the two structures. The SHMOKE data have been corr elated with tunneling measurements on similarly fabricated structures. For the two samples listed above, the junction resistivity varied from 10(-1) O mega cm(2) (plasma oxidized) to 10(-6) Omega cm(2) (thermally oxidized). Th ese results indicate that SHMOKE may be useful for assessing tunnel junctio n quality during processing. [S0021-8979(99)49408-3].