  Fabrication of a multistrip magnetic/nonmagnetic structure in a thin
sandwiched Ni layer [Si(5 nm)/Ni(10 nm)/Si] by a focused ion beam (FIB)
irradiation has been attempted. A control experiment was initially performed by
irradiation with a standard 30 keV Ga ion beam at various fluences. Analyses
were carried out by Rutherford backscattering spectrometry, X-ray reflectivity,
magnetooptical Kerr effect (MOKE) measurements and MOKE microscopy. With
increasing ion fluence, the coercivity as well as Kerr rotation decreases. A
threshold ion fluence has been identified, where ferromagnetism of the Ni layer
is lost at room temperature and due to Si incorporation into the Ni layer, a
Ni0.68Si0.32 alloy layer is formed. This fluence was used in FIB irradiation of
parallel 50 nm wide stripes, leaving 1 micrometer wide unirradiated stripes in
between. MOKE microscopy on this FIB-patterned sample has revealed interacting
magnetic domains across several stripes. Considering shape anisotropy effects,
which would favor an alignment of magnetization parallel to the stripe axis,
the opposite behavior is observed. Magneto-elastic effects introducing a
stress-induced anisotropy component oriented perpendicular to the stripe axis
are the most plausible explanation for the observed behavior.
