On the origin of oblique-incidence anisotropy in evaporated cobalt films

Abstract

The main results obtained when studying a temperature dependence of the uniaxial anisotropy of oblique-incidence magnetic films of cobalt are given. It has been stated that when depositing the films onto a substratum heated to 350°C, the easy magnetization axis (EA) is perpendicular to the incidence plane of a molecular beam (a positive anisotropy). EA is in the incidence plane (a negative anisotropy) when the temperature of a substratum is 60 to 80°C. At intermediate temperatures of a substratum a positive anisotropy arises at small angles of deposition and a negative one is at great angles of deposition. Temperature dependences of the constant of the uniaxial anisotropy for samples with a positive or negative anisotropy distinguish between each other. In samples with a positive anisotropy this constant changes with the temperature as a square of magnetization; in samples with a negative anisotropy at less than room temperatures, this constant is approximately proportional to the anisotropy constant of a massive-cobalt single crystal. The obtained results have been considered from the theoretical point of view, and it has been concluded that a negative anisotropy in oblique-incidence films arises as a result of formation of very small grains stretching in the direction of the incidence plane and having a significant anisotropy of the magnetic energy in layers adjoining the boundaries (the Néel anisotropy). Observation of the typical temperature dependence of the anisotropy constant of these samples is a very convincing proof of existence of the Néel anisotropy.