Magnetic and transport properties of discontinuous Ni81Fe19/Al2O3 multilayers

The structural percolation and its correlation with the magnetic and transport properties of Ni81Fe19/Al2O3 multilayer films were studied by varying the thickness (t) of the Ni81Fe19 (permalloy, Py) layers in the range of 10-16 angstrom, while keeping the Al2O3 layer thickness constant at 16 angstrom. Low-angle X-ray reflectivity and transmission electron microscopy measurements revealed a good structural quality of the multilayers and showed the transition from continuous Py layers (t = 16 angstrom) separated by Al2O3 layers to grains (t = 10 angstrom) dispersed in the insulating matrix. Magnetization measurements showed the gradual transition from ferromagnetic layers (t = 16 angstrom) to superparamagnetic clusters (t = 12 angstrom) and isolated grains (t = 10 angstrom) that successively become blocked as the temperature decreases. The temperature dependence of the current in-plane (CIP) resistance of the samples reveals a change from typical metallic (dR/dT > 0) to dielectric (dR/dT < 0) conductance as the Py layer thickness decreases from 16 to 10 angstrom. (c) 2006 Elsevier B.V. All rights reserved.