Abstract
The structural percolation and its correlation with the magnetic and transport properties of Ni 81 Fe 19 / Al 2 O 3 multilayer films were studied by varying the thickness ( t) of the Ni 81 Fe 19 (permalloy, Py) layers in the range of 10–16 Å, while keeping the Al 2 O 3 layer thickness constant at 16 Å. 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 A ˚ ) separated by Al 2 O 3 layers to grains ( t = 10 A ˚ ) dispersed in the insulating matrix. Magnetization measurements showed the gradual transition from ferromagnetic layers ( t = 16 A ˚ ) to superparamagnetic clusters ( t = 12 A ˚ ) and isolated grains ( t = 10 A ˚ ) 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 ( d R / d T > 0 ) to dielectric ( d R / d T < 0 ) conductance as the Py layer thickness decreases from 16 to 10 Å.
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