Magnetic domain structure and imaging of Co-Pt multilayer thin-film nanostructures

Dots, with diameters of 100 nm and 220 nm, have been fabricated from (Co_xPt_{0.8 nm})₂₅ multilayer structures, where the Co thickness x was varied from 0.2 nm to 0.45 nm. The unpatterned films show perpendicular anisotropy with perpendicular coercive fields of 20 kA/m to 100 kA/m. The patterned structures show a transition from multidomain to single domain behavior as the dot dimension is reduced from 220 nm to 100 nm. The remanent hysteresis loops of the 100 nm dots were measured using magnetic force microscopy (MFM) and compared to remanent hysteresis loops of the unpatterned films. MFM line scans of the 100 nm dots were compared to calculations of the field gradients expected above uniformly magnetized dots. The calculations indicate that narrow features in the magnetic field gradients should be observed near the edges of the dots and that these samples may be of use as a magnetic imaging resolution standard