Effect of Neel coupling on magnetic tunnel junctions

We have studied the effect of the dipolar magnetic coupling (also known as Neel coupling or "orange-peel" coupling) in tunneling magnetoresistive (TMR ) elements. With an in situ scanning tunneling microscope we directly acces sed the roughness of the films and found a close correspondence between the values for the coupling fields determined by the magneto-optical Kerr effe ct and the ones computed on the basis of the measured morphology parameters . We confirm an increase of the dipole coupling between the magnetic layers with decreasing barrier thickness as predicted by the model. Deviations fr om the theoretical predictions are observed for the case of thinner soft ma gnetic layers, which can be explained by reduced magnetization in very thin films. We demonstrate the importance of dipolar coupling for understanding the magnetic behavior of TMR elements by comparing TMR curves for optimize d and nonoptimized structures. (C) 2001 American Institute of Physics.