Micromagnetics of ultrathin films with perpendicular magnetic anisotropy

Abstract

Magnetization processes in ultrathin transition-metal films with perpendicular magnetic anisotropy are investigated. By model calculations it is shown that nucleation in ideal films is incoherent and therefore bulklike, whereas the truly ultrathin limit of coherent nucleation is restricted to film patches of small cross-section areas. In ideal monolayers, the nonzero film thickness leads to bulklike nucleation if the lateral dimensions of the film exceed about 1 m. This means that monolayer patches having submicrometer diameters cannot be regarded as ultrathin in a micromagnetic sense. On the other hand, the critical single-domain diameter of ultrathin films is larger by one order of magnitude than expected from bulk-type thin-film calculations.

Curie temperature of multiphase nanostructures

“…This must be compared with the ''micromagnetic'' coupling length ͑ex-change length͒ a 0 /␣ϭ7.52 nm, where ␣ϭ1/137 is Sommerfeld's fine structure constant. 19 To explain this difference we note that the inhomogenity T o (r)ϪT in Eq. ͑2͒ is analog to the inhomogenity term 2K 1 (r)Ϫ 0 H N M s in Ref.…”

Asymmetric Domain Nucleation and Unusual Magnetization Reversal in Ultrathin Co Films with Perpendicular Anisotropy

“…Another potential cause for the formation of local unidirectional anisotropy is the exchange coupling between islands with ferromagnetic and antiferromagnetic (AF) order [26 -30]. The AF ordering may occur due to oxidation of some Co islands and formation of CoO [26], at the interface steps [27], or at the Co surface like in an Fe=W 001 ultrathin film [30]. These potential causes were not supported by further experiments.…”

Multidomain and incoherent effects in magnetic nanodots

“…Since typical ferromagnets have magnetizations of the order of 1 T a͒ Author to whom correspondence should be addressed; electronic mail: rskomski@neb.rr.com and exchange stiffnesses of the order of 10 pJ/m, l ex is between 1 and 2 nm for a broad range of materials. 5,9 The magnetostatic self-interaction term favors magnetic domains with partial or complete flux closure which are separated by comparatively narrow domain walls. 1,2,7,8,10 The self-interaction energy competes against the domain-wall energy, and domain formation in spheres is favorable when the radius is larger than the critical single-domain radius R SD ϭ36ͱAK 1 / 0 M s 2 .…”