The micromagnetic exchange stiffness is a critical parameter in numerical modeling of magnetization dynamics and reversal processes, yet the current literature reports a wide range of values even for such simple and widely used material as Cobalt.With use of ab-intio estimated Heisenberg parameters we calculate the low temperature micromagnetic exchange stiffness parameters for hexagonal-close-packed (HCP) and face-centred cubic Cobalt without previous and our own. For HCP Co they are slightly different in the directions parallel and perpendicular to the c-axis. We establish the exchange stiffness scaling relation with magnetization A(m) ∼ m 1.8 valid for all sets of parameters for a wide range of temperatures. For HCP Co we find an anisotropic domain wall width in the range 24 − 29 nm which increases slowly with temperature. The results form a critical input for large-scale temperature-dependent micromagnetics simulations and demonstrate the importance of correct parameterization for accurate simulation of magnetization dynamics.
Fe 3 O 4 nanoparticles are one of the most promising candidates for biomedical applications such as magnetic hyperthermia and theranostics due to their bio-compatibility, structural stability and good magnetic properties. However, much is unknown about the nanoscale origins of the observed magnetic properties of particles due to the dominance of surface and finite size effects. Here we have developed an atomistic spin model of elongated magnetite nanocrystals to specifically address the role of faceting and elongation on the magnetic shape anisotropy. We find that for faceted particles simple analytical formulae overestimate the magnetic shape anisotropy and that the underlying cubic anisotropy makes a significant contribution to the energy barrier for moderately elongated particles. Our results enable a better estimation of the effective magnetic anisotropy of highly crystalline magnetite nanoparticles and is a step towards quantitative prediction of the heating effects of magnetic nanoparticles. arXiv:1909.02470v1 [cond-mat.mes-hall] 5 Sep 2019 2/16 10/16 16/16
Understanding the domain wall dynamics is an important issue in modern magnetism. Here we present results of domain wall displacement in curved cylindrical nanowires at a constant magnetic field. We show that the average velocity of a transverse domain wall increases with curvature. Contrary to what it is observed in stripes, in a curved wire the transverse domain wall oscillates along and rotates around the nanowire with the same frequency. These results open the possibility of new oscillation-based applications.
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