MAGNETIZATION REVERSAL IN THIN CU NI/CU/SI(001) FILMS/

A step wedged structure of the form 30 Angstrom Cu/50 Angstrom Ni/h An gstrom Cu/Si(001) (h = 600, 1000, 1500, 2000 Angstrom) grown by MBE ha s been characterised by in situ RHEED and ex situ polar MOKE magnetome try and MOKE microscopy. The magnetisation reversal process was invest igated through measurements of hysteresis loops, magnetisation relaxat ion and domain images. The sample exhibits a strong magnetic aftereffe ct and the macroscopic relaxation measurements were fitted by a model which assumes thermally activated magnetisation reversal through domai n nucleation and domain-wall propagation. Magnetic imaging confirms th at domain-wall propagation dominates over domain nucleation at all Cu buffer layer thicknesses. For the 600 Angstrom Cu buffer layer, strong domain-wall pinning occurs on a micron scale, whereas for the 2000 An gstrom Cu a domain-wall can propagate freely over hundreds of microns. The reduced pinning causes the coercive field to decrease as the Cu b uffer thickness increases. The Barkhausen length deduced from fits to the relaxation data increases with Cu buffer thickness. The correlatio n length at the Cu buffer and Ni overlayer surface as obtained from th e width of the RHEED streaks also increases, suggesting an interdepend ence between the crystallographic properties of the buffer and overlay er and the magnetic properties.