We investigate the interlayer coupling between two thin ferromagnetic (F)
films mediated by an antiferromagnetic (AF) spacer in F*/AF/F trilayers and
show how it transitions between different regimes on changing the AF thickness.
Employing layer-selective Kerr magnetometry and ferromagnetic-resonance
techniques in a complementary manner enables us to distinguish between three
functionally distinct regimes of such ferromagnetic interlayer coupling. The F
layers are found to be individually and independently exchange-biased for thick
FeMn spacers - the first regime of no interlayer F-F* coupling. F-F* coupling
appears on decreasing the FeMn thickness below 9 nm. In this second regime
found in structures with 6.0-9.0 nm thick FeMn spacers, the interlayer coupling
exists only in a finite temperature interval just below the effective N\'eel
temperature of the spacer, which is due to magnon-mediated exchange through the
thermally softened antiferromagnetic spacer, vanishing at lower temperatures.
The third regime, with FeMn thinner than 4 nm, is characterized by a much
stronger interlayer coupling in the entire temperature interval, which is
attributed to a magnetic-proximity induced ferromagnetic exchange. These
experimental results, spanning the key geometrical parameters and thermal
regimes of the F*/AF/F nanostructure, complemented by a comprehensive
theoretical analysis, should broaden the understanding of the interlayer
exchange in magnetic multilayers and potentially be useful for applications in
spin-thermionics.Comment: 14 pages, 9 figure