Structural and magnetic analysis of Ni81Fe19/Ag multilayers with ultrathin Ni81Fe19 sublayers

The magnetic and structural properties of Ni81Fe19/Ag multilayer films with very thin sublayers of the magnetic Ni81Fe19 component, ranging from 5 Angstrom to 10 Angstrom, were studied. A transition from a nearly pure superparamagnetic behaviour (t(NiFe) = 5 Angstrom) to a nearly ferromagnetic behaviour (t(NiFe) = 10 Angstrom) was observed, with a transition at the Ni81Fe19 layer thickness of about 7 Angstrom. The observed differences in magnetic properties are thought to be mainly connected with the size of the NiFe particles in the magnetic sublayers, which can be controlled by their thickness. The structure of the magnetic sublayers becomes more disturbed with decreasing thickness, as can be judged from the in-plane correlation length, roughness, and strain, and the numbers of precipitated crystallites of the two components. The influences of various annealing processes were examined, and the structural changes were followed in situ by high-angle x-ray diffraction (XRD). The temperature treatment increased the magnetoresistance ratio. We observed a gradual growth of the content of silver and NiFe precipitates with increasing annealing, temperature. The structure of the original multilayers gradually deteriorates with increasing temperature, and the whole complex consists of a mixture of residual multilayer blocks and precipitates. The observed structural characteristics of the multilayers under study have been found essential to the understanding of their magnetic properties.