Magnetization distribution at the surface of Co-Cr films:magneto-optical, chemical and structural characterization

In magnetic high density recording media, the Wonnation is stared in the domain structure at the surface of thin films. Chemical, structural and magnetic properties at the surface plar an important role in the reading and writing process. In this thesis the results of an investigation on sputtered Co-Cr films, a most promissing high density recording medium, are presented. Special attention is pared to the upper 50 nm of the films, which is indicated as surface. It appeared from XPS and Auger experiments that the oxidized scale on room temperature annealed RF- and MRF-sputtered Co81Crl9 films was abaut 6 nm thick and consisted of three different larers. The topology as investigated br SEM, AFM and STM appeared to be stronglr related to the film's column morphology. The roughness amplitude varied trom 6 nm for the thinner films to 50 nm for the thick Co-Cr films. In order to investigate the magnetism at the surface of these films a combined optical and magneto-optical measurement srstem has been built, based on a polarizer film rotating analrser ellipsometer. The dielectric tensor elements were determined and appeared ta be stronglr dependent on the morphology of the film under investigation. It can be concluded from these results and those of others, that the Kerr rotation can be considered ta be linearlr dependent on the magnetization. Hrsteresis curves could be measured very accuratelr with the intensity technique. Major, minor and in-plane loops as weIl as the angle dependencr of the magnetizatian were studied br Kerr tracer and V SM. The differences between the measurement results obtained br bath methods can be explained br demagnetizing effects and film in- homogenities. A model was developed in order to calculate the influence of roughness, oxidatian- segregation surface larers and closure domains on the maximum readable infarmatian density .It can be concluded from the results of this calculation, that the recording performances of next generation media will be limited br the surface properties. A large surface loss is expected for linear bit densities in the order of 30 Mbit/m. "Closure damain loss" can be avoided br increasing the Q-factor of the thin film medium

A combined optical and magneto-optical measurement system

A magneto-optical (MO) Kerr tracer based on an ellipsometer was developed for studying the surface magnetic properties of thin films. This system can be used to measure the optical properties n and k, which are strongly related to the magneto-optical parameters qk and hk. In order to carry out measurements on materials having a small qk we have developed a multiple reflection sample holder which gives an enhancement of the rotation. The behavior of the sample holder is explained in terms of Jones matrices. The optical and magneto-optical properties for a thickness series of Co-Cr films were measured. Comparative measurements on other systems gave similar results

Surface properties and stray fields of RF-sputtered CoCr films

The influence of surface properties on the recording performance of thin films is at best illustrated in the perpendicular recording mode. The roughness and the oxidated/segregated top layer will redistribute the magnetic charges at the surface. The stray field which is so important in the reading process will deteriorate. Attention will be focussed on the relation between the stray field and magnetization (J.J. Miyata et al., IRE Trans. Elect. Comp. (1959) 159) as a function of the above mentioned properties. Using experimental data the reduction of the maximum readable information density is calculated

Surface chemical state of sputtered Co-Cr films

Surface oxidation states of sputtered Co80Cr20 (at%) films were studied by performing Auger Electron Spectroscopy (AES) and X-ray Photoemission Spectroscopy (XPS). Seven samples having different thicknesses (from 50 to 1000 nm) which were grown under the same conditions have been studied. It was found from these experiments that among all the films the initial oxidation occured in the Cr; the the following diffusion of the Co was observed at the top layer. Consequently the surface consists of a four-layered structure. A weak thickness dependence in the films of the oxidized region was found from the results of AES measurements. The change of the saturation magnetization through the sample was calculated using the results of AES and XPS data. These calculations show that a region with enhanced saturation magnetization can be expected under the non-ferromagnetic top layer