Dependence of the interlayer coupling on anneal temperature in Ni-Fe/Cu evaporated multilayers

Resistivity and magnetization studies of [Ni₈₃Fe₁₇(27 Å)|Cu(37 Å)]₁₀ multilayers, grown by electron-beam evaporation, reveal that the magnetoresistance (ΔR/R) increases from <0.3% to 4.4% following a heat treatment at 325 °C. Polarized neutron reflectivity measurements on annealed samples show that the interlayer coupling changes from ferromagnetic to anaferromagnetic, confirming the conclusions of the bulk studies. Data for the 300 and 325 °C annealed samples in small fields show a magnetic peak at half-order that is absent for the as-deposited and 275 °C annealed multilayers. Some of the Ni-Fe spins in the annealed multilayers are thus ordered in large (> 100 μm) in-plane domains aligned antiparallel across the Cu layers. An increase in the magnetic scattering at low angles indicates that some of the remaining Ni-Fe moments are randomly oriented from one layer to the next.