The structure of cobalt based multilayer thin films

Two of the more commonly studied topics in the general area of magnetic multilayer thin films are giant magnetoresistance (GMR) (particularly in relation to its application in magnetic recording technology) and magnetic recording media. In addition to electron microscopy, x-ray diffractometry and magnetometry experiments, the rapidly developing technique of grazing incidence reflectivity has been applied in this work to the study of GMR in Co/Cu multilayers, the propagation of interfacial structure through a multilayer stack, and magnetisation switching field distributions in CoCrPt based multilayer recording media. Firstly the apparent relationship between GMR, antiferromagnetic (AF) coupling and crystallographic texture in sputter deposited polycrystalline Co/Cu multilayers is reported. It is found that the GMR decreases from a typical literature value in a randomly oriented multilayer to a very low value of less than 2% in multilayers with a strongly defined <111> fibre texture. The concomitant loss of AF coupling as shown by polarised neutron reflectivity (PNR) and magnetometry techniques is striking. The relationship between these three dramatic changes is as yet unclear. Secondly the progression of interfacial texture through multilayers with increasing numbers of bilayers is followed be x-ray reflectivity. Comparisons are made between Co/Pt multilayers, which exhibit a pronounced columnar growth mechanism, and Co/Cu multilayers of similar dimensions which show no significant change in interfacial texture through the stack. The differences are attributed to disparities in the surface free energies between the two systems. Finally the magnetic switching behaviour of CoCrPt/Cr/CoCrPt trilayer structures is followed by magnetometry and PNR investigations. It is shown that, as the thickness of the Cr spacer layer is increased from 0 nm to 10 nm the switching behaviour goes from unimodal (i.e one single switching event) to bimodal. Computer modelling of the PNR data indicates that the upper magnetic layer has the lower coercivity of the two. This change in magnetic structure is attributed to microstructural changes as elucidated by transmission electron microscopy and x-ray diffraction investigations. (author)Available from British Library Document Supply Centre-DSC:DXN027899 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo