A Quantum Exchange Bias Model for Coupling Across a Nonmagnetic Interlayer

Exchange bias (EB) has been observed in systems where a paramagnetic (PM) spacer separates an antiferromagnet (AFM) from a ferromagnet. This coupling extends to PM spacer thicknesses of up to 100Å in Py/(Ag, Au, Cu)/CoO systems. We develop a quantum fluctuation model in which a dipole field is created at the AFM surface due to the breaking of translational invariance symmetry. The uncompensated spins of the semiinfinite AFM induce a field that extends all the way to the CoO/(Ag, Au, Cu) interface and thus generate EB. The magnitude of the EB field that the present model yields is of the same order of magnitude as the one measured in recent experiments.