Magnetoresistive properties of 1st AFM Co/Cu multilayers sputtered in an Ar+O 2 atmosphere
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Magnetoresistive properties of 1st AFM Co/Cu multilayers sputtered in an Ar+O2 atmosphere D. Kubinski, M. Parsons and J. Hangas Ford Research Laboratory MD3028/PO Box 2053, Dearborn, MI 48121-2053 ABSTRACT Sputter-deposited Co/Cu multilayers at the 1st antiferromagnetic maximum (tCu= 9Å) exhibit large magnetoresistance and low relative hysteresis and are attractive for use in many position sensor applications. Unfortunately, their large magnetoresistance values can be hard to reproduce, perhaps a consequence of the difficulties in growing flat, pin-hole free layers. In this study we demonstrate that their magnetoresistive properties can be improved with the addition O2 to the Ar sputtering gas. A sequence of [Co(15Å)/Cu(9Å)]20 multilayers were made using magnetron sputtering in a 2mTorr Ar+O2 atmosphere, with the O2 concentration ranging from 20%) only for the first few films deposited after venting our vacuum system with air. This is evident in Fig. 1 which demonstrates the decrease in the maximum magnetoresistance for each sequential deposition made after venting. As a reproducibility check, data for two sequences are shown. For sequence #1, the magnetoresistance dropped to only ~4% after nine depositions. Note that prior to the 11th deposition the vacuum chamber was vented to air again and the subsequent film showed a large increase in magnetoresistance. The base pressure varied only slightly during these sequences. For example, for sequence #2 the base pressure dropped from 2.7x10-8 Torr to 2.4x10-8 Torr after five depositions. Motivated in part by the study showing that residual O2 in the deposition chamber improved the performance of Co/Cu spin valves [6], it was demonstrated that the magnetoresistive properties of our sputter deposited 1st AFM Co/Cu MLs could be improved by bleeding O2 into the chamber prior to deposition [5]. The improvements in the magentoresistance, however, were later found to be hard to reproduce. In this study we report the effects of the magnetoresistive properties of 1st AFM Co/Cu MLs upon adding O2 directly to the Ar sputtering gas. FILM GROWTH TECHNIQUES AND CHARACTERIZATION A sequence of [Co(15Å)/Cu(9Å)]20 ML films were grown in a 2mT Ar+O2 atmosphere using d.c. magnetron sputtering. The molar O2 concentration ranged from
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