Brillouin light scattering from magnetic thin films and multilayers

Brillouin light scattering (BLS) from spin-waves has evolved into a valuable optical probe for the investigation of magnetic thin films and multilayers to accurately determine magnetisations, anisotropies, and exchange parameters. Such structures have stimulated research due to their unique properties and possible applications in the magnetic recording, magneto-optic recording, transducer and sensor industries. In this study, BLS has been used to analyse a number of samples consisting of a variety of materials, interlayer spacers, and substrates, prepared under different conditions. The major part of this work is experimental yet a significant proportion required the development of a numerical model to analyse the results. The major results are summarised as follows: (i) BLS measurements examining the effect of post-deposition oxidation on TbFeCo thin films confirm a two layer model of a weakly ferrimagnetic film, partially oxidised, forming a thin magnetically active surface layer. Significantly, the thickness of this layer is determined to be of the order of 20 nm. (ii) BLS measurements investigating the type and degree of magnetic coupling in a series of Co/Cr/Co trilayers demonstrate that dipolar coupling is strong and dominates the spin-wave response. The effect of exchange coupling is found to be small even for a 0.5 nm Cr spacer. (iii) BLS studies of structurally inhomogeneous FeCo/X (X = Ag, Cu ) multilayers reveal some intriguing features. Primarily, a disparity between bulk and observed magnetisation values is rationalised by a volume averaged magnetisation model. The results are evidence that BLS is a good diagnostic tool even for systems with a complex microstructure. (iv) A BLS study of Ni/Pt multilayers is compared with one by vibrating sample magnetometry (VSM). The VSM model includes the presence of an unusual magnetically dead Ni-Pt alloy interface layer. The BLS measurements not only substantiate the existence of the alloy layer but place more accurate bounds on its thickness. (v) BLS measurements on a series of Co/Cu multilayers showed magnetisations reduced from the bulk Co value. A reinterpretation of the BLS results enabled a more favourable agreement with results from ferromagnetic resonance experiments. Analysis of the results required the development of a computational numerical technique based on a theory taken from the literature. Both dipolar and exchange interactions, and surface and volume anisotropic effects on the dispersion of spin-waves are included in a macroscopic model. A Fortran computer program has been written and was used to enhance the understanding of the results. (author)Available from British Library Document Supply Centre-DSC:DXN029127 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo