Pure amorphous Co thin film3 (> 100 A thick) have been prepared by condensation onto liquid helium cooled glass substrates. Evaporation wa3 accomplished with the electron bombarded pendant drop technique in pressures of 10 Torr. In-situ measurements were made of the electrical resistivity and Mossbauer emission spectra of the films during annealing to room temperature. The films underwent an abrupt and irreversible drop in resistivity, characteristic of metallic films at the amorphous to crystalline transition. This three to fourfold decrease occurred ax 53 °K for the purest films (99.6? purity), the transition temperature increasing with increasing impurity content.
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