Ellipsometric Characterization for Multilayers Containing Magneto-Optic TbFeCo Films
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Ellipsometric Characterization for Multilayers Containing Magneto-Optic TbFeCo Films M. Ruane
A. Jain
Boston University, College of Engineering, 44 Cummington Street, Boston, MA 02215 USA
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ABSTRACT
Multilayered structures containing sputter-deposited films of amorphous TbFeCo can exhibit magneto-optical Kerr rotation and are leading candidates for erasable optical storage media. Ellipsometric characterization of optically active multilayered media is desirable during media development, testing and production, but traditional ellipsometry does not account for the presence of optical activity. A novel ellipsometer is described that can characterize both the dielectric overcoat and the optically active layers. Reflectivity measurements are collected for different incident angles and polarizations using a differential detector while the magnetic reversibility of the active film layer is exploited to enhance the magneto-optical signal from the TbFeCo. A multilayer film model is used to process observations and estimate media characteristics. The model explicitly accounts for the optical activity of the TbFeCo layer, and is parameterized in terms of the index of refraction and thickness of the overcoat, and the real and imaginary parts of the elements of the dielectric tensor of the active layer. A series of TbFeCo films with varying composition, rf-sputter deposited on quartz substrates with A1203 dielectric protective overcoats, is characterized. Both Tb-rich and Fe-rich samples were deposited, with room temperature coercivities ranging from 1.6kOe to about 4kOe, and film-side Kerr rotations between 21 minutes and 28 minutes. Reflectivity data versus angle of incidence, and estimated dielectric tensor elements for the TbFeCo layers are presented. A standard figure of merit, based on the off-diagonal tensor elements, is used to compare competing media in terms of their optimal performance in a multilayered structure.
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INTRODUCTION
Erasable magneto-optical media have been the subject of intense development because they offer high density data storage, optical write/read operations and ease of handling. A variety of amorphous binary and ternary rare-earth transition-metal (RE-TM) alloys have been studied as possible media. Appropriate compositions support perpendicular anisotropy and the thermomagnetic writing of perpendicular reverse magnetized domains. Readout uses the polar Kerr effect.1- 3 In a previous paper, we reported on the characterization of binary TbFe alloys that were sputter-deposited on quartz substrates 4 and coated with glass.
Mat. Res. Soc. Symp. Proc. Vol. 103. ©1988 Materials Research Society
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Compared to TbFe binary films, amorphous TbFe( o alloys have exhibited greater resistance to corrosion and are more likely candidates for practical magneto-optical disk systems. This paper describes extensions of our earlier characterization efforts to include ternary TbFeCo films with A1 2 0 3 overcoat layers. Media will be described in terms of their dielectric tensor elements, which can be use
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