Magnetic Properties of Reactive Co-Sputtered NiFe-Oxide Samples

Abstract

In this paper, we discuss the properties of reactive radio-frequency-sputtered Fe-doped NiO thin films co-sputtered at different oxygen flow rates. The films were deposited in an AJA Orion sputtering system from metallic NiFe-19 at.% targets. The deposition rate was monitored before and after deposition using a quartz crystal monitor. The deposition rate at the sample location depends strongly on the O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flow. At lower oxygen flows, the deposition rate increases with oxygen flow caused by the oxidation of the sample. At higher oxygen flow rates, the deposition rate decreases with increasing oxygen flow. This is caused by poisoning of the targets resulting in a lower deposition rate. The oxygen content of the samples increases with the oxygen flow rate. This conclusion is supported by vibrating sample magnetometer measurements that show an increase in the magnetic moment for films sputtered at lower O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> flows. To determine the chemical state of the elements, the X-ray photoelectron spectroscopy (XPS) analysis of the samples was carried out ex situ on films capped with a Pt or Au layer. Prior to the XPS measurements, part of the cap layers but not all were removed with an Ar sputtering gun in the XPS chamber. The XPS results show that the ratio of the Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> -Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> atoms in the film decreases with the oxygen flow. The Fe-XPS spectra of the films sputtered at different oxygen flows look very similar to each other but different from XPS studies done on oxidized permalloy by others showing that RF-sputtered NiFe-oxide is different from oxidized permalloy. The comparison of the XPS data for the samples sputtered at 20 sccm covered with Pt cap and Au cap was also done and shows smaller metallic Ni peaks for the sample capped with Au than samples capped with Pt, possibly caused by partly sputtering through the cap layer for the Pt-capped samples influencing the stoichiometry of the top layer of the NiFe-oxide.