Atomic structure and thermal stability in amorphous rare‐earth–transition‐metal magneto‐optic alloys (abstract)

Abstract

The technique of EXAFS has been used to study local atomic structure and thermal stability in amorphous thin‐film alloys of TbFe, TbFeCo, TbFeCoAu, and DyFe. The rare‐earth–transition‐metal (RE‐TM) films used were coated on the underside and topside by additional dielectric layers of Si3N4 to prevent oxidation during annealing. The EXAFS data were obtained by direct measurement of sample current in a total electron yield technique of data collection. The applicability of this method of analysis to the particular magneto‐optic sample structure used is discussed with results of atomic local site geometry and limitation of the technique. Calculations from Fe K‐edge data in TbFe and TbFeCo samples yield an Fe nearest‐neighbor distance of 2.50±0.10 Ã… and an average coordination number of 11.0 representative of a dense random‐packed amorphous structure. On annealing to 400 °C a second‐nearest‐neighbor distance and second shell structure is observed in the radial distribution functions as bccFe precipitates into the amorphous matrix. The addition of small amounts of Au into the RE‐TM alloy is shown to stabilize the amorphous structure and prevent this process of atomic rearrangement of Fe through a process of stearic pinning. Analysis of Tb Liii–edge data is also discussed in addition to measurements of magnetic parameters Hc and Ku relevant to application in optical storage media. © 1988, American Institute of Physics. All rights reserved.