Grain-boundary micromagnetism

Abstract

Abstract-Continuum and layer-resolved calculations are used to investigate the spin structure in the vicinity of grain boundaries. Reduced exchange in the grain-boundary region gives rise to a quasidiscontinuity of the magnetization and yields a perturbation which decays exponentially inside the grains. An effective intergranular exchange is obtained as a micromagnetically well-defined function of the grain-boundary exchange, and it is discussed how grain boundaries affect the hysteresis loops of nanostructures.

Are there superspin glasses?

“…The magnetocrystalline anisotropy is ignored in these calculations, but their inclusion is straightforward. 22 For grains that touch each other with a contact area pR c 2 , as in Fig. 1(b), it is reasonable to assume that the magnetization change is localized in a volume of order 4pR 3 /3.…”

Spin structure at nanojunctions and constrictions

“…8,9 In the past, theoretical research has largely focused on quasione-dimensional structures, which have been tackled by phenomenological continuum and atomicresolution methods. [10][11][12][13][14] From a theoretical point of view, the spin structure at granular interfaces and in constrained domain walls was first investigated in the context of polycrystalline rare-earth transition-metal intermetallics, 10 although various earlier articles, such as Refs. [15][16][17][18][19], anticipate much of the involved physics.…”

“…13,14 Furthermore, the reduced exchange at interfaces gives rise to a quasidiscontinuity of the magnetization. In the absence of external fields it has a relative strength of 1/(1ϩ2AЈ␦ o /AD), where D is the thickness of the interface, and A and AЈ are the exchange stiffnesses in the bulk and in the interface region, respectively.…”

“…14 A detailed comparison of continuum and atomically resolved models yields only minor corrections due to the discrete nature of the layerresolved model. 13,14 A common feature of the above-mentioned structures is their one-dimensional nature, but many geometries of interest in spin electronics are quite complicated and cannot be described in terms of planar models. One key aspect of this article is to discuss three-dimensional effects.…”

Magnetic impurities in magic-number clusters

“…To exploit the catalytic potential of nanoparticles, it is necessary to stabilize the magnetization at the reaction temperature. This may be achieved by using several magnetic impurities per cluster, by a moderate pressure to realize an effective exchange coupling 11,12 between particles, and/or by using catalytically inert particles such as Fe as exchange bridges.…”