| The Interlayer Exchange Coupling (IEC) of magnetic multilayers has been one of the most studied problems in condensed matter physics for the last decade. It is found that for a multilayer structure in which magnetic layers are separated by a spacer, the magnetic moments of each layer orient themselves parallel, antiparallel or even perpendicular to each other, depending on the thickness of the spacer. This variable interlayer coupling of the magnetizations is oscillatory and usually multiperiodic. Its determination has posed interesting challenges, because often calculated results differ from the experimental ones. From the application standpoint, multilayer structures are used in the new generation of recording heads. In the first part of the present work, we used the Reflection Amplitude Approximation (RAA) to calculate the coupling in the prototypical system of an Fe/Cr trilayer. We were able to identify the origin of the long period oscillation in the coupling, and obtain a coupling strength that was among the best theoretical predictions. In the second part, we used a more accurate method that employed the so called Analytical Green Function (AGF). The results of this approach offered a good checkpoint of RAA, and they were in good agreement with the experimental findings in Fe/Cr and Co/Cu systems. We then calculated the intrinsic biquadratic coupling and compared it to the extrinsic one, obtained from the thickness fluctuation model. We also studied the effect that the finite thickness of the magnetic layers may have on the coupling, in particular in the appearance of Fano resonances. Finally, we studied how the coupling changes when roughness, alloying of the spacer, or strain are present. In all cases, the results were in very good agreement with experiment, showing that the AGF method is a very accurate, and yet very efficient method, for the determination of the IEC. |
