Magnetostriction and Stress in High Moment FeTaN Films
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MAGNETOSTRICTION AND STRESS INHIGH MOMENT FeTaN FILMS J. C. CATES-, G. QIU**, E. HAFTEK**, C. ALEXANDER, JR.*, and J. A. BARNARD**
The University of Alabama, *The Department of Physics and Astronomy and **The Department of Metallurgical and Materials Engineering, Tuscaloosa, AL 35487-0202 ABSTRACT
Magnetostriction and thin film stress have been studied in high moment single layer FeTaN films deposited by high rate reactive dc magnetron sputtering. Low magnetostriction ( magnitude less than 1 x 10-6) can be obtained over a fairly large0 range of nitrogen flow rates during film deposition by vacuum annealing at 500 C. After annealing at 5000C for two hours, all films were found to be in a state of tensile stress. Stress versus temperature measurements up to 4000C show film stress in as-deposited films to be highly hysteretic during the first temperature cycle reflecting the films' processing history. Stress-temperature cycles on annealed samples indicate that extremely stable films are produced in an intermediate range of nitrogen content. 1. INTRODUCTION
As coercivities in recording media increase, a growing emphasis has been placed on developing materials with a high saturation magnetization for high density magnetic recording heads. Potential materials must also exhibit a low coercivity, high permeability, small magnetostriction, and suitable corrosion and thermal properties. Because of their high moment, FeN-based materials have been examined and show considerable potential for application in high-density thin film recording heads. The addition of small amounts of Ta to the FeN films has been shown to improve the soft magnetic properties and enhance corrosion resistance in these films[1-3]. Domain structure is extremely important inoptimizing the performance of the thin film recording head. The magnetoelastic anisotropy, which is proportional to the product of the magnetostriction and film stress, is used to control the domain structure in thin film heads. The interrelationship and importance of stress and magnetostriction has recently been addressed[4]. Inthis paper, the dependence of magnetostriction and film stress on deposition conditions and annealing are examined in FeTaN films. In a companion paper[5] we report on the very promising soft magnetic properties of a similar set of FeTaN films. 2. EXPERIMENTAL METHODS
Single layer FeTaN films were deposited on glass substrates at ambient temperature by dc magnetron reactive sputtering in a Vac-Tec Model 250 Batch Side Sputtering System. The hot pressed Fe target contained approximately 10 w/o Ta which produced films containing 3.2 a/o Ta. The thickness of the films in this study is -420 nm; deposition rates were 1-1.5 nm/sec. The Ar flow rate was set at 60 sccm and the N2 flow rate varied from 0 to 25 sccm. The N content in the films increased linearly with N2 flow rate (approximately 0.36 a/o N per sccm N2). Vacuum annealing at 5000C was performed at -10-6 torr. Magnetostriction was measured in an AC magnetostriction tester based on a design by Tam and Scr
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