Magnetization Reversal in CoPt Magnetooptic Recording Alloys
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Magnetization Reversal in CoPt Magnetooptic Recording Alloys
T. Kleinefeld*, W.S. Kim*, J. Valentin* and D. Weller** * Universitat Duisburg, FB 10/ Angewandte Physik, Postfach 101503, D-4100 Duisburg, Germany ** IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, CA 951206099, USA
ABSTRACT High resolution Kerr microscopy has been used to study newly developed Co 2 5 Pt 7 5 alloy films with perpendicular magnetic anisotropy. In particular, the dynamics of magnetization reversal processes wase investigated by means of time resolved domain pattern analysis. Domain wall motion dominated magnetization reversal as well as nucleation dominated processes were observed. Magnetic aftereffect phenomena were confirmed by relaxation measurements of magnetic domains. The fractal dimension of the observed domains is correlated to the macroscopic coercivity determined from hysteresis loop measurements.
INTRODUCTION Thin metallic films of alloys of Co and Pt have recently been discussed as promising new materials for magnetooptic recording applications [1]. The advantages of these alloys compared with other recording materials were clearly pointed out in recent publications [1-3]. The process of magnetization reversal is of particular interest because of its important role in thermomagnetic recording. Special interest is focused on the formation of magnetic domains and the stability of the domain shape after reversal of the magnetization in the writing laser spot. Therefore the magnetic aftereffect is considered to be one of the limiting factors in magnetooptic recording applications. In this paper we present a study of the magnetization dynamics using Kerr microscopy and successive image processing. In addition, quasi static hysteresis loops for the present Co 2 5 Pt 7 5 samples with uniaxial perpendicular anisotropy could be determined with this method. The shape of these hysteresis loops basically coincide with that from conventional polar MOKE loops [5].
Mat. Res. Soc. Symp. Proc. Vol. 313. 91993 Materials Research Society
316
EXPERIMENTAL The determination of domain patterns is based on a polarisation microscope setup described elsewhere [6]. The imaging is based on the polar Kerr effect. Image acquisition is performed with a highly resolving CCD-Camera with linear response in intensity. By using frame data averaging in a fast real-time image processor we were able to reduce the noise and drastically enhance the contrast in the domain imaging. Subtracting background images further improves the quality of the data. Co 2 5 Pt 7 5 alloy films were prepared by e-beam evaporation in high vacuum with a base 0 pressure of - 10-8 mbar at a typical deposition temperature of about 220 C. Polished Si(100) substrates were used with 400A thick SiNx etched buffer layers [7]. Alloys were obtained by subatomic layering of Pt and Co as described previously [1-2]. The final composition was determined with x-ray fluorescence. Typical film thicknesses cover the range from d=100 A to d=300 A. All measurements were carr
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