The effect of roughness on the micromagnetic properties of high moment multilayer films

Abstract

Electron microscopy has been used to determine directly the effect of artificially introduced roughness on the micromagnetic processes that occur in soft high moment multilayer films. The nanodefects, introduced to roughen the substrate, and the local magnetic domain structure were identified in the same images, leading to unambiguous information on the role played by the former. Characteristic of the micromagnetic state of the samples was a high density of 360° wall segments that showed quite remarkable resistance to annihilation. Following a description of the domain walls generated in both easy and hard axis magnetization cycles, a model is proposed for the way the observed domain walls respond when their ends are strongly pinned and, using this, we account for their continued existence over an extended number of magnetization cycles. Finally, the implications for device performance are discussed briefly.

Almost quantum correlations

“…In this paper we present an outer approximation to the set of quantum correlations which we term 'almost quantum'. This approximation has appeared before in the scientific literature under different names and in completely different contexts, such as quantum information science [25], graph theory (see [15,16] for references) and quantum gravity [17]. Inspired by these surprising connections, we will present a series of results that support the conjecture that the set of almost quantum correlations does actually emerge from a reasonable physical theory.…”

“…In the bipartite case, Lemma 3 allows us to identifyQ with the set Q 1+AB , defined in [13] as an approximation to the set of quantum correlations for applications in quantum information theory. Q 1+AB can also be interpreted, by Definition 1, as the set of bipartite probability distributions admitting a strongly positive decoherence functional [17], see [19] for a proof 1 . Finally, in any non-locality scenario defined by the hypergraph H, the setQ can be identified with the set of probabilistic models p such that ϑ(Ort(H), p) = 1 [15,16].…”

Concentric 360° domain wall nesting in magnetic tunnel junction films: a Lorentz TEM study

“…The cross-sectional electron microscopy images clearly indicate interfacial roughness throughout the S2 stacks, which is known to influence magnetisation reversal, in particular the formation and annihilation of 360° DWs. Indeed, artificially-created nanodefects have previously been used for DW pinning [34]. Our data suggest the presence of pinholes within the barrier layer; these would produce ferromagnetic bridges across the barrier and act as pinning centres during the magnetic reversal processes.…”

“…In this case, the appearance of these defects is consistent with a particulate in one of the layers and such physical artefacts are known to perturb the local magnetisation of the surrounding layers [34] to form 360° DWs [17,18]. In other cases, the physical identity of the defect is less obvious.…”

“…parallel to the applied magnetic field. Note also that the DW in figure 6(c) assumed a zigzag shape, a low-energy configuration that avoids the formation of extended charged head-to-head 180° DWs and maximises the alignment with respect the EB direction, at the expense of a slightly increased wall length [34,35].…”