Physical Properties of Thin Metallic Films. III> The Effect of Temperature on the Change of Resistance of Bismuth Films in A Magnetic Field.

Abstract

Ageing of sputtered bismuth films.---The films sputtered on glass between sputtered gold terminals, were sealed in glass tubes and kept in vacuo at 210-220\ifmmode^\circ\else\textdegree\fi{} C. for a number of hours. As a result each film showed a gradual decrease of resistance amounting in all to about 40 per cent. Eventually the films became so thoroughly aged that temperature-resistance measurements in vacuo could be accurately reproduced over long periods.Increase of resistance of bismuth films in a magnetic field for temperatures from - 190\ifmmode^\circ\else\textdegree\fi{} to 230\ifmmode^\circ\else\textdegree\fi{} C.---The isothermal curves obtained for each film by varying the field up to 18,000 gauss, have the same form for all temperatures, differing only by constant factors, and closely resemble the corresponding curves for bismuth in bulk. The percentage increase of resistance is not proportional to the square of the field. It is greater the lower the temperature and the lower the resistance, that is, the thicker the film, reaching a value about 1/5 that of bismuth for the thickest film tested.Variation of resistance of bismuth films with temperature, - 190\ifmmode^\circ\else\textdegree\fi{} to 230\ifmmode^\circ\else\textdegree\fi{} C.---The curves are parabolic in form, showing a minimum around 150-200\ifmmode^\circ\else\textdegree\fi{} C.; the lower the resistance of the film, the lower the temperature of minimum resistance.Electrically heated oil bath.---It is suggested that bakelite is a suitable material for protecting the nichrome heater.