UHV Mössbauer Emission Spectra of Thin Iron Films

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Abstract
Mössbauer emission spectra are used to determine relaxation effects of 57Fe in thin iron films deposited at 10−9 Torr and measured at 10−11 Torr. The spectra from the radioactive films have been analyzed at room temperature, liquid nitrogen, and 15°K over a range of thickness from 3×1016 atoms/cm2 to 0.12×1016 atoms/cm2 (25–1 Å). Samples thinner than 7 Å show the following characteristics: a positively resolved doublet interpreted as quadrupole splitting of about 0.6 mm/sec independent of thickness and temperature; a normalized resonance area roughly constant with temperature; one line increases in width and area and the other decreases as the temperature is lowered. Samples thicker than 10 Å are approximately characteristic of bulk iron. The transition is ascribed to superparamagnetic fluctuations in the internal field but the detailed line shapes are not simply explained. A multilayer 25‐Å sample has six lines in the normal positions at 15° and 80°K, but the outer lines show a decreasing intensity as the temperature increases until they vanish at room temperature.

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