Non-Magnetic Films of Nickel

Abstract

Properties of sputtered nickel films.---(1) Magnetic. These films, prepared by sputtering in hydrogen on to a cooled surface, with a 1000 volt d.c. generator, are initially non-magnetic, showing neither magneto-optic rotation nor tractive effects in a magnetic field. After heating to 300\ifmmode^\circ\else\textdegree\fi{} or 400\ifmmode^\circ\else\textdegree\fi{}C, however, they become strongly magentic and exhibit both these effects. Films much thicker than 120m\ensuremath{\mu}, or those sputtered with an induction coil, are likely to be magnetic from the start. (2) Crystal structure. X-ray spectrograms by the powder method show for the heat-treated (magnetic) film the face-centered cubic lattice as for ordinary nickel, but prove that the original non-magnetic film is amorphous. These facts suggest that ferro-magnetism in nickel, at any rate, is not a property of the individual atom as customarily supposed, but of the crystalline aggregate. A number of possible objections to this point of view are taken up and discussed. (3) Electric. The gain in magnetic properties on heat-treatment is accompanied by a decrease of resistance to a fraction (a fifth in one case) of its initial value. The original film also gives only about 1 percent of the Hall effect that it does after heat-treatment. (4) Color. Some films, particularly those deposited on a surface at liquid-air temperatures, display remarkable colors. On examination of the reflected light with a spectroscope, only a narrow spectral region is seen to be absent. If the nickel films are thin, covering with an optically dense liquid completely destroys the colors.