Ion irradiation effects on a magnetic Si/Ni/Si trilayer and lateral magnetic-nonmagnetic multistrip patterning by focused ion beam

TL;DR

This study investigates how focused ion beam irradiation modifies the magnetic properties of a Si/Ni/Si trilayer, enabling the creation of patterned magnetic/nonmagnetic multistrip structures with controllable ferromagnetism and domain interactions.

Contribution

It demonstrates the use of FIB irradiation to selectively alter magnetic properties and form multistrip patterns, revealing stress-induced anisotropy effects in the process.

Findings

Ferromagnetism is lost at a specific ion fluence due to Si incorporation.

Patterned stripes exhibit interacting magnetic domains contrary to shape anisotropy expectations.

Stress-induced anisotropy explains the observed magnetic behavior across stripes.

Abstract

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.