Magnetization reversal of nanostructured Co/Pt multilayer dots and films studied with magnetic force microscopy and MOKE

• Published in: IEEE transactions on magnetics 1999-09, Vol.35 (5), p.3106-3111
• Main Authors: Carl, A., Kirsch, S., Lohau, J., Weinforth, H., Wassermann, E.F.
• Format: Article
• Language: English
• Subjects: Coercive force; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Interfacial magnetic properties (multilayers, magnetic quantum wells, superlattices, magnetic heterostructures); Large-scale systems; Length measurement; Magnetic analysis; Magnetic field measurement; Magnetic force microscopy; Magnetic hysteresis; Magnetic multilayers; Magnetic properties and materials; Magnetic properties of surface, thin films and multilayers; Magnetization reversal; Perpendicular magnetic anisotropy; Physics
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/20.801098

Large scale periodic arrays of magnetic nanostructures consisting of e.g. Co/Pt multilayer dots with perpendicular magnetic anisotropy are possible candidates for future high-density magnetic storage media. We have fabricated periodic dot-arrays by optical interference lithography with Ar/sup +/ ion lasers operating at wavelengths of 457 nm and 244 nm, respectively. Periodicities range from 125 nm to 1100 nm with dot diameters between 70 nm and 740 nm covering a total area of up to 20 cm/sup 2/ with a maximum dot density of about 4.1/spl times/10/sup 10/ dots/in/sup 2/. The global magnetic properties of these Co/Pt dot-arrays and of corresponding homogeneous films are investigated by the magneto-optical Kerr effect (MOKE) in polar geometry. Results of the magnetization reversal are compared to magnetic force microscopy (MFM) investigations in external magnetic fields of up to H=1 kOe perpendicular to the sample. A simple MFM-data analysis is described which allows to determine hysteresis loops from a series of MFM images obtained in various external magnetic fields. This then allows to measure the coercivity H/sub c/ of a given sample on small length scales. A comparison with MOKE hysteresis loops shows good agreement, although the unknown hysteretic behavior of the tip cannot be separated. The MFM-image analysis described therefore stands as a semi-quantitative method, which is however useful to measure relative changes of the coercivity on small length scales.