Atomic structures of amorphous Tb19Fe81, Tb20Fe52Co28, Tb19Fe26Co55 and Tb19Co81 films of 1 μm thickness grown on quartz glass substrate have been studied by X-ray diffraction. Atomic distances and coordination numbers in these films were obtained and the essential structural features of these films appear to be unchanged by the variation of composition. It is found that the transition metals, Fe and Co are in direct contact with the surrounding atoms and preferentially surrounded by Tb. The structural change by annealing at 473 K in the amorphous Tb20Fe52Co28 film was also investigated. The interference function of the annealed sample is slightly shifted to higher-Q and the peaks corresponding to the TM-TM and TM-Tb pairs (TM=Fe or Co) in the reduced radial distribution function are enhanced and their locations are shifted to lower-r with increase in annealing time. These results imply that the smaller size transition metals mainly change their position during low-temperature annealing while the variation in the position of Tb atoms having the larger size is not clearly detected.
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