Ion irradiation effects on a magnetic Si/Ni/Si trilayer and lateral magnetic–nonmagnetic multistrip patterning by focused ion beam
2017
Fabrication of a multistrip magnetic/nonmagnetic structure in a thin sandwiched Ni layer [Si(5 nm)/Ni(15 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
fluencehas 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
fluencewas used in FIB irradiation of parallel 50 nm wide stripes, leaving 1 µm wide unirradiated stripes in between. MOKE microscopy on this FIB-patterned sample has revealed interacting
magnetic domainsacross several stripes. Considering shape anisotropy effects, which would favour an alignment of magnetization parallel to the stripe axis, the opposite behaviour 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 behaviour.
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