Long-range exchange coupling between a ferromagnet and an antiferromagnet across a nonmagnetic spacer layer

The antiferromagnet/ferromagnet exchange coupling giving rise to a shifted hysteresis loop has usually been considered an interfacial effect. We show evidence that this exchange coupling between an antiferromagnet (CoO) and a ferromagnet (Ni81Fe19) is long range in nature. Exchange coupling has been observed in tri-layer films consisting of a nonmagnetic noble metal (Ag, Au, and Cu) spacer layer sandwiched between 300 Å CoO and 300 Å NiFe. The strength of the coupling decreases with increasing spacer layer thickness and vanishes at about 55 Å. This suggests that the antiferromagnetic/ferromagnetic exchange coupling is beyond an interfacial effect, and that conduction electrons may be involved in the mediation of the coupling.