Correlation of tunnel magnetoresistance with magnetic switching in Co/AlOx/Ni81Fe19cross-strip structures

We describe the fabrication and characterization of cross-strip Co/AlO x /Ni 81 Fe 19 magnetic tunnel junction (MTJ) structures with area of 0.01 mm 2 . The MTJs were deposited by magnetron sputtering through a series of masks and the AlO x tunnel barrier was formed by plasma oxidation of a thin Al layer. Two sets of MTJs were fabricated in which the thicknesses of the magnetic electrodes were approximately 1000 and 100 Å. We have studied the magnetic switching of both the strip electrodes and the junction area by magneto-optical Kerr effect magnetometry, and have measured the anisotropic magnetoresistance characteristics of the electrodes, and the tunnel magnetoresistance (TMR) of the junction area. TMR values of up to 18% were observed at room temperature. The easy axes of the two electrodes are in general canted apart and the coupling is found to be significantly stronger in the junctions with thicker electrodes. A single domain model provides a good qualitative description of the switching and TMR for all field azimuths. However, the measured TMR is less sensitive to the orientation of the applied field than the model predicts. This is attributed to the presence of pinning that enhances the coercivity of the Co hard axis hysteresis loop.