Magnetic and transport properties revealing a structural percolation in Ni81Fe19-Al2O3 multilayers

This study presents the structural, magnetic and transport properties of a series of Ni₈₁Fe₁₉-Al₂O₃ granular multilayer films. The multilayers were prepared by sequential deposition of Ni₈₁Fe₁₉ (Permalloy, Py) and Al₂O₃ on thermally oxidized Si(001) substrates by DC and RF sputtering, respectively. The thickness t of the Al₂O₃ layers was kept constant at 16 , while the nominal thickness of the Py layers was varied in the range from 8 to 16 . Low-angle X-ray reflectivity (XRR) measurements and alternating gradient magnetometry (AGM) at room temperature, in conjunction with variable temperature magneto-optical Kerr effect (MOKE) and measurements of temperature dependent electrical resistance were applied for evaluation of the structural and magnetic properties of the multilayers. Results show that transition from ferro-to superparamagnetic behavior and from metallic to dielectric conductance imply a structural percolation, where the magnetic films change from forming continuous layers to particles as the Py layer thickness decreases from 16 to 10 .