Magnetoresistance origin for nonresonant microwave absorption in antiferromagnetically coupled epitaxial Fe/Cr/Fe(001) sandwiches

Nonresonant microwave-absorption signals have been observed in a series of molecular-beam-epitaxy-grown Fe/Cr/Fe (001) sandwiches which were previously shown to exhibit an antiferromagnetic coupling of the two Fe layers. Using field-modulation detection, one observes signals which display an unusual magnetic-field dependence containing sharp features in the range 0–2 kOe. The magnetic-field locations of these features are independent of the microwave frequency, but their intensity depends strongly on the field-modulation amplitude. The features also have a strong in-plane angular dependence. Comparison with earlier magnetization and magnetoresistance data on the same samples shows that a sharp feature occurs when the magnetization orientations in the Fe films change abruptly, and that one can explain the microwave-absorption signals in terms of magnetoresistance effects in the sandwich. Thus, microwave absorption provides a contactless way to investigate the magnetoresistance in such samples.