Numerical analysis of the domain structure of Fe-Co-C and Co/Ni-Co films

Abstract

This work deals with the formation of magnetic domains in thin ferromagnetic films. It gives a short introduction to domain theory and introduces existing analytical meth- ods for the description of narrow stripe domains. The main focus is on the numerical analysis of two alloy layers whose understanding of their magnetic behavior may lead to the development of possible new materials. The research was realized in the form of micromagnetic simulations and concentrated mainly on the static magnetic distri- bution of these structures. The purpose of these simulations was to reproduce and complement experiments performed by K. Leistner et al. on Co/Ni-Co films and by V. Neu et al. [1] on tetragonally distorted Fe-Co-C films. The first structure is a cobalt layer, with varying thickness, on top of four Co/Ni multi-layers. Depending on the thickness of the cobalt layer, the material has a homogeneous in-plane magnetization below a critical thickness and switches to perpendicular oriented magnetization as the thickness is getting larger. This critical thickness has been calculated to be 0.437 nm and could be verified using ”magnum.fe” as the simulation software. The second set of simulations was performed on Fe-Co-C films with varying thickness in the range of 30 nm − 110 nm. For this structure, it has been found that for a thickness above 45 nm the magnetization distribution represents a stripe domain structure. The width of these stripes increases with the thickness of the sample. The dependence between the thickness of the film and the stripe width as well as the critical thickness at which the stripes appear was investigated. For this purpose a new one period simulation method was developed and tested on the basis of various experimental results. Fur- thermore, the influence of material parameters on the magnetization as well as the stray field above the structure was identified.