Oblique-Incidence Magnetic Anisotropy in Codeposited Alloy Films

Abstract

Alloy films produced by simultaneous deposition from two separate sources, one evaporating NiFe and the other evaporating a nonferromagnetic metal X, can exhibit large oblique-incidence ferromagnetic anisotropy even for small-incidence angles. For vapor-beam angles of NiFe high compared with those of X, the simultaneous deposition causes a large increase in the value of the magnetic anisotropy over that produced by oblique incidence of the NiFe alone; for vapor-beam angles of X high compared with those of NiFe the oblique incidence of X controls the production of the anisotropy. The values of the magnetization dispersion and the wall coercive force Hw increase with the X concentration. For high X concentrations magnetic-viscosity phenomena may appear, while for sufficient X concentration the magnetic anisotropy of the film is destroyed. These effects were exhibited by films of NiFe with Ag, Al, Au, Pb, Sn, Zn, and Cu, but NiFeCu films were most extensively studied. Various measurements showed that the presence of X did not promote the growth of the crystallite chains which cause the oblique-incidence anisotropy in pure NiFe films. Instead, it is suggested that X metal is distributed at the crystallite interfaces in a layer which is so thin that it is not directly detectable, but which is thick enough to weaken or destroy the intercrystalline exchange bonds. Oblique incidence causes the interfacial layer of X around a given crystallite to be thicker in the direction of that vapor beam having the higher incidence angle, thus leading to magnetic anisotropy. When the X concentration and/or the deposition temperature is sufficiently high, X becomes isotropically distributed around each crystallite and each crystallite tends to become magnetically independent. This causes high magnetization dispersion, magnetic-viscosity effects (thermally induced magnetization fluctuations), and eventual destruction of the anisotropy.