Long-range oscillatory exchange interaction between antiferromagnetic FeMn layers across a Cu spacer

The exchange interaction between antiferromagnetic FeMn layers across a Cu spacer is studied by employing the exchange bias as a probe in multilayers of ``NiFe∕thin $\mathrm{Fe}\mathrm{Mn}∕\mathrm{Cu}∕\text{thick}$ FeMn.'' With variation of the Cu spacer's thickness, the indirect exchange interaction, monitored through the response of the exchange bias, oscillates with a period of approximately $18--20\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, about twice that for ferromagnetic films separated by a Cu spacer. This result shows that long-range oscillatory exchange interaction is a basic and universal feature in both metallic ferromagnetic layers separated by nonmagnetic metals and metallic antiferromagnetic layers separated by a nonmagnetic metal, due to the quantum interferences induced by the spin-dependent interface reflection of Bloch waves with different oscillating periods originating from the difference in interface reflection conditions between ferromagnetic and antiferromagnetic spin ordering.