Saturation Magnetization of Nickel Films of Thickness Less Than 100 A

Abstract

Nickel films varying in thickness from 200 to 3 A were prepared by evaporation on glass substrates in a vacuum sufficiently high to prevent gas adsorption on the film during preparation and measurement. Their magnetization was measured as a function of field up to 10 000 oe using a vacuum torsion magnetometer. The saturation magnetization of these films was determined as a function of their thickness at 300\ifmmode^\circ\else\textdegree\fi{}K and 77\ifmmode^\circ\else\textdegree\fi{}K. No decrease in saturation magnetization from that of bulk nickel has been observed for films of thickness down to 20 A, at room temperature. The Curie temperature of a 27 A film was found to coincide with that of bulk nickel. The magnetic behavior of films in the thickness range below 20 A suggests superparamagnetism rather than a decrease in the saturation magnetization. Measurements of the magnetostrictive anisotropy constant indicate that the films as originally prepared are in a state of high tensile strain, which can be relieved by annealing. The thin film nature of some specimens was ascertained by examination in the electron microscope.