PUB - Publikationen an der Universität Bielefeld

The work of this thesis has to be seen in the context of magnetoresistive phenomena and their applications. It was the aim of this thesis, to implement a new material system, an amorphous CoFeB alloy, and to study its properties in magnetic tunnel junctions (MTJ). Main focus was the investigation of the coupling phenomena in these materials and the effect for their technical application. The work is relevant for application in magnetoresistive devices and partly has been carried out within the project "Magnetoresistive logic devices". In order to compete with the rapid downscaling in feature size of silicon semiconductors, the spin-dependent devices will also have to be scaled down to the sub-micrometer range. In the second part of this thesis, therefore, the concept of an Artificial Ferrimagnet (AFi) has been transferred to elements of sub-micrometer size. In order to get access to this small scale at experiments, patterning has been performed by electron-beam lithography, leading to sizes comparable to recent MRAM devices. In order to characterize the resulting patterns, a magneto-optical Kerr effect setup has been purchased, installed, and modified. A systematic study of the switching behavior as well as the related coupling phenomena at sub-micrometer size is presented. Emphasis is given at the interlayer exchange coupling and the exchange bias effect. Most of the phenomena for spin-dependent devices listed above are relevant for the discussion of the measurements presented in this thesis. Therefore, the first chapter covers a short introduction to most of them. The second chapter highlights the measurement methods used within this thesis. In the third chapter, the experimental results are presented and discussed. This chapter is separated into three main sections, covering the experiments at unpatterned magnetic multilayers, at patterned samples, and the studies of exchange bias effect. In the last chapter, the thesis is summarized and an outlook for further interesting investigations is given. In the appendix, the software and hardware modifications done at the magneto-optical Kerr effect setup are presented.