title: Magnetic dipole and higher pole interaction on a square lattice.
abstract: We have studied the magnetic interaction of circular magnetic islands with a dipole character on a square lattice. The square pattern consists of lithographically prepared polycrystalline PdFe islands, 150 nm in diameter and a periodicity of 300 nm. Below the Curie temperature at 260 K, the islands are in a single domain state with isotropic in-plane magnetization. Below 160 K, there is an onset of interisland interaction that leads to a change of the shape of the hysteresis, an increase of coercivity, and a development of in-plane anisotropy. Photoemission electron microscopy with circularly polarized incident x rays tuned to the L3 edge of Fe confirms the increasing correlation of the magnetic islands and the formation of elongated chains, as predicted by Vedmedenko et al. [Phys. Rev. Lett. 95, 207202 (2005)] for contributions from pole interactions of higher order than the dipolar one. Neighboring chains are found to be irregularly oriented either parallel or antiparallel.
authors.affiliation: Institut für Experimentalphysik/Festkörperphysik, Fakultät für Physik and Astronomie, Ruhr-Universität Bochum, Bochum 44780, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Ewerlin
authors.forename: Derya
authors.initials: D
authors.lastname: Demirbas
authors.forename: Frank
authors.initials: F
authors.lastname: Brüssing
authors.forename: Oleg
authors.initials: O
authors.lastname: Petracic
authors.forename: Ahmet A
authors.initials: AA
authors.lastname: Ünal
authors.forename: Sergio
authors.initials: S
authors.lastname: Valencia
authors.forename: Florian
authors.initials: F
authors.lastname: Kronast
authors.forename: Hartmut
authors.initials: H
authors.lastname: Zabel