778 research outputs found
Fe/V and Fe/Co (001) superlattices: growth, anisotropy, magnetisation and magnetoresistance
Some physical properties of bcc Fe/V and Fe/Co (001) superlattices are
reviewed. The dependence of the magnetic anisotropy on the in-plane strain
introduced by the lattice mismatch between Fe and V is measured and compared to
a theoretical derivation. The dependence of the magnetic anisotropy (and
saturation magnetisation) on the layer thickness ratio Fe/Co is measured and a
value for the anisotropy of bcc Co is derived from extrapolation. The
interlayer exchange coupling of Fe/V superlattices is studied as a function of
the layer thickness V (constant Fe thickness) and layer thickness of Fe
(constant V thickness). A region of antiferromagnetic coupling and GMR is found
for V thicknesses 12-14 monolayers. However, surprisingly, a 'cutoff' of the
antiferromagnetic coupling and GMR is found when the iron layer thickness
exceeds about 10 monolayers.Comment: Proceedings of the International Symposium on Advanced Magnetic
Materials (ISAMM'02), October 2-4, 2002, Halong Bay, Vietnam. REVTeX style; 4
pages, 5 figure
Low energy sputtering of Mo surfaces
Surfaces of materials subject to irradiation will be affected by sputtering, which can be a beneficial effect, like in the coating industry where a material is sputtered and redeposited on to another material to coat it. However, in most cases sputtering is an unwanted side-effect, for instance in nuclear fusion reactors, where the wall material will be degraded. This effect needs to be understood in order to be able to predict its consequences. To understand the sputtering, on an atomistic level, we have thoroughly investigated molybdenum surface sputtering by computational means. Molybdenum was chosen as detailed experimental studies have been carried out on it and it is one candidate material for the diagnostic mirrors in ITER, facing the plasma. In this study, we thoroughly investigate the molybdenum samples of different surface orientations, and their response to low energy argon plasma irradiation, by molecular dynamics simulations. We find both a surface orientation and ion energy specific sputtering yield of the samples, and a very good agreement with the experiments available in the literature. A few different setups were investigated to observe differences as well as to understand the key features affecting the sputtering events. The different simulation setups revealed the optimal one to represent the experimental conditions as well as the mechanisms behind the observed discrepancies between different modelling setups. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).Peer reviewe
CASCADE DEBRIS OVERLAP MECHANISM OF <100> DISLOCATION LOOP FORMATION IN Fe AND FeCr
Two types of dislocation loops are observed in irradiated alpha-Fe, the 1/2 loop and the loop. Atomistic simulations consistently predict that only the energetically more favourable 1/2 loops are formed directly in cascades, leaving the formation mechanism of loops an unsolved question. We show how loops can be formed when cascades overlap with random pre-existing primary radiation damage in Fe and FeCr. This indicates that there are no specific constraints involved in the formation of loops, and can explain their common occurrence. Copyright (C) EPLA, 2017Peer reviewe
Memory Effect, Rejuvenation and Chaos Effect in the Multi-layer Random Energy Model
We introduce magnetization to the Multi-layer Random Energy Model which has a
hierarchical structure, and perform Monte Carlo simulation to observe the
behavior of ac-susceptibility. We find that this model is able to reproduce
three prominent features of spin glasses, i.e., memory effect, rejuvenation and
chaos effect, which were found recently by various experiments on aging
phenomena with temperature variations.Comment: 10 pages, 14 figures, to be submitted to J. Phys. Soc. Jp
Effect of cascade overlap and C15 clusters on the damage evolution in Fe : An OKMC study
In order to investigate the long-term evolution of radiation-induced defects in the fission- and fusion-relevant material iron, we introduce cascade overlap effects into Object Kinetic Monte Carlo simulations. In addition to cascade overlap, we study the effect of introducing discrete C15 Laves phase clusters into the simulations. By applying either, none, or both of these effects we identify how they influence the evolution of the system. We find that both cascade overlap and C15 clusters affect the evolution of the radiation damage in different ways and on different time scales. Cascade overlap is found to reduce the number of Frenkel pairs. On the other hand, the explicit consideration of C15 Laves phase clusters increases the accumulation of defects at low dose. The results are compared to Molecular Dynamics simulation results under similar conditions.Peer reviewe
Collision cascades overlapping with self-interstitial defect clusters in Fe and W
Overlap of collision cascades with previously formed defect clusters become increasingly likely at radiation doses typical for materials in nuclear reactors. Using molecular dynamics, we systematically investigate the effects of different pre-existing self-interstitial clusters on the damage produced by an overlapping cascade in bcc iron and tungsten. We find that the number of new Frenkel pairs created in direct overlap with an interstitial cluster is reduced to essentially zero, when the size of the defect cluster is comparable to that of the disordered cascade volume. We develop an analytical model for this reduced defect production as a function of the spatial overlap between a cascade and a defect cluster of a given size. Furthermore, we discuss cascade-induced changes in the morphology of self-interstitial clusters, including transformations between 1/2 and dislocation loops in iron and tungsten, and between C15 clusters and dislocation loops in iron. Our results provide crucial new cascade-overlap effects to be taken into account in multi-scale modelling of radiation damage in bcc metals.Peer reviewe
Numerical Study of Aging in the Generalized Random Energy Model
Magnetizations are introduced to the Generalized Random Energy Model (GREM)
and numerical simulations on ac susceptibility is made for direct comparison
with experiments in glassy materials. Prominent dynamical natures of spin
glasses, {\it i.e.}, {\em memory} effect and {\em reinitialization}, are
reproduced well in the GREM. The existence of many layers causing continuous
transitions is very important for the two natures. Results of experiments in
other glassy materials such as polymers, supercooled glycerol and orientational
glasses, which are contrast to those in spin glasses, are interpreted well by
the Single-layer Random Energy Model.Comment: 8 pages, 9 figures, to be submitted to J. Phys. Soc. Jp
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