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 Angstrom CoO and 300 Angstrom NiFe. The strength of the coupling decreases with increasing spacer layer thickness and vanishes at about 55 Angstrom. 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. (C) 1997 American Institute of Physics.