Abstract
Two-dimensional lattices of dipolar-coupled thin film ferromagnetic nanodisks can give rise to emergent ‘superferromagnetic’ (SFM) order when the spacing between dots becomes sufficiently small. This allows for the design of metamaterials, which can be tailored to have a specific type of long-range order magnetic order by tuning the lattice symmetry. We have previously shown experimentally that a square lattice symmetry gives rise to antiferromagnetic order, and a hexagonal lattice gives rise to ferromagnetic order. In the present study, we pattern the arrays into micron sized hexagons, squares, and rectangles in order to investigate shape anisotropy as an effect of the finite-size for such arrays. The magnetic domain patterns were examined using XPEEM and were found to be below their blocking temperature at room temperature. Due to lithographic defects, the dots were found to feature a slight ellipticity, thus giving rise to a shape anisotropy that overwhelmed the anisotropy of the array shape. Distinct differences were found in the magnetic switching characteristics of horizontally and vertically oriented rectangular arrays which was corroborated by micromagnetic simulations.
*We used resources of the ALS, which is a U.S. Department of Energy Office of Science User Facility under Contract No. DE-AC02-05CH11231. S.D.S. acknowledges support from the ALS Doctoral Fellowship in Residence. Partial funding was obtained from the European Union's Horizon 2020 FET—Open program under Grant Agreement No. 861618 (SpinENGINE) and the Norwegian Ph.D. Network on Nanotechnology for Microsystems, which is sponsored by the Research Council of Norway, Division for Science, under Contract No. 221860/F60. The Research Council of Norway is acknowledged for support of the Norwegian Microand Nanofabrication Facility, NorFab, under Contract No. 245963/F50.
