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

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.     

On the stability of certain magnetic modes in fine ferromagnetic particles

Conditions of stability of the magnetization curling mode in fine spherical and cylindrical particles and of the magnetization helicoid structure in fine cylindrical particles are derived, and magnetization reversal processes in such particles are considered. The application of Ritz's method for solving the variational problem of finding the local magnetization vectors in the volume of a particle provides a convenient way of finding the conditions mentioned above. It has been shown that the magnetization curling mode in a spherical fine particle with radius larger than a critical one is stable in a well-determined interval of the external magnetic field, provided the magnetocrystalline anisotropy constant is less than a certain value K0. In such a case the hysteresis loop of a spherical particle measured in an easy direction is no longer rectangular. The magnetization curling and helicoid modes are both unstable in fine cylindrical particles with positive or zero values of the magnetocrystalline anisotropy constant. The hysteresis loop of such particles magnetized along the axis of rotation is rectangular.