Magnetic and transport properties of discontinuous Ni81 Fe19/Al2O3 multilayers

Artikel i vetenskaplig tidskrift, 2007

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 over(A, ̊)) separated by Al 2 O 3 layers to grains (t = 10 over(A, ̊)) dispersed in the insulating matrix. Magnetization measurements showed the gradual transition from ferromagnetic layers (t = 16 over(A, ̊)) to superparamagnetic clusters (t = 12 over(A, ̊)) and isolated grains (t = 10 over(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. © 2006 Elsevier B.V. All rights reserved.