COO-NIO SUPERLATTICES - INTERLAYER INTERACTIONS AND EXCHANGE-ANISOTROPY WITH NI81FE19

A strong interlayer exchange interaction is observed in polycrystallin e antiferromagnetic CoO-NiO thin-film superlattices. This was determin ed by measuring the exchange field H(e) resulting from coupling these superlattices with Ni81Fe19. The temperature above which H(e) is zero (the blocking temperature) is taken as a measure of the ordering tempe rature of the superlattice. In CoO-NiO superlattices with short repeat distances the CoO and NiO layers order at a single temperature that i s between the ordering temperatures of bulk CoO and NiO. These orderin g temperatures are the same as for CoxNi1-xO alloy films with the same overall composition. The temperature dependence of H(e) in some of th e superlattice exchange couples deviates from the linear behavior expe cted for cubic antiferromagnets. In addition, the exchange anisotropy induced by some CoO-NiO superlattices is greater than that induced by CoxNi1-xO. The higher H(e) and nonlinear temperature dependence sugges t that the interlayer coupling has a strong effect on the magnetocryst alline anisotropy of the layers within the superlattice. Thick-NiO/thi n-CoO/Ni81Fe19 trilayers were produced to investigate the thickness de pendence of the oxide-oxide interaction. When the CoO layers are suffi ciently thin (less-than-or-equal-to 20 angstrom), the CoO ordering tem perature approximates the NiO value, indicating quite strong coupling throughout the CoO layer. The effect of the coupling is much weaker fo r thicker CoO layers (> 30 angstrom).