Microstructural Dependence of the Perpendicular Magnetic Anisotropy in Co-Pt Alloys
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OF DEPENDENCE MICROSTRUCTURAL MAGNETIC ANISOTROPY IN Co-Pt ALLOYS
THE
PERPENDICULAR
E. E. Marinero, R. F. C. Farrow, G. R. Harp, R. H. Geiss, IBM Research Division,
Almaden Research Center, 650 Harry Road, San Jose, CA 95120-6099; .1. A. Bain and B. Clemens, Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305. ABSTRACT
To establish the structural origins of the perpendicular magnetic anisotropy in Co-Pt alloys, a variety of magnetic and structural characterization techniques have been utilized. We have determined that the development of out-of-plane magnetization in these alloys, strongly depends on growth temperature and in contrast to Co/Pt multilayers, the highest anisotropies and coercivities are observed in polycrystalline alloys with negligible preferred crystallographic orientation. Lattice strain measurements, surface roughness determination and crystal growth studies indicate that contributions from magnetostrictive and magnetostatic contributions to the perpendicular anisotropy in these alloys are not significant. HRTEM and synchrotron-based x-ray diffraction experiments, on the other hand, confirm the existence of ordered CoPt 3 at elevated temperatures. We suggest that the strong temperature dependence of the perpendicular anisotropy is correlated to the onset of spontaneous chemical ordering during the growth which results in anisotropic pair ordering. A tentative model explaining this strong temperature dependence is described. I. INTRODUCTION
The presence of perpendicular anisotropy in Co-Pt alloys was first demonstrated by Treves et alt). In their work they demonstrated that the formation of the tetragonally ordered CotPtr-LIo phase was key to the development of perpendicular anisotropy. Ordering was obtained by annealing at 600'C their-sputter deposited alloy films. More recently, Lin and Gorman(2) reported perpendicular anisotropy in evaporated Cot1 xPtx near the 1:3 composition. In their work, they found that fcc [Ill] texturing promoted by growing the alloys on Pt buffer layers at growth temperatures of around 200'C was required. Further studies by Weller et alt3) on the magnetic and magneto-optical properties of these alloys indicates that the intrinsic Kerr rotation of said alloys at short wavelengths is considerably higher than equivalent multilayers containing the same volume content of Co atoms. This makes this class of materials extremely attractive for high density magneto-optical recording. To study the origins of the perpendicular anisotropy, we have utilized in this work, MBE growth of CoxPt1 -x (x-0.25) alloy films deposited onto substrates of amorphous carbon, amorphous SiN and fused silica at temperatures ranging from 30 to 500'C. The results are compared with those for highly [Ill] oriented epitaxial alloy films grown onto basal-plane sapphire substrates under identical conditions. EXPERIMENTAL TECHNIQUES
The films were grown in a MBE system (VG Semnicon-Fisons VG 80M) in a background pressure of below 2x10- t Torr. Co-evaporation from el
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