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° or 400°C, however, they become strongly magentic and exhibit both these effects. Films much thicker than 120mμ, 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.