| 1. |
- Nicolas, Aude, et al.
(författare)
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Genome-wide Analyses Identify KIF5A as a Novel ALS Gene
- 2018
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Ingår i: Neuron. - : Cell Press. - 0896-6273 .- 1097-4199. ; 97:6, s. 1268-1283.e6
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Tidskriftsartikel (refereegranskat)abstract
- To identify novel genes associated with ALS, we undertook two lines of investigation. We carried out a genome-wide association study comparing 20,806 ALS cases and 59,804 controls. Independently, we performed a rare variant burden analysis comparing 1,138 index familial ALS cases and 19,494 controls. Through both approaches, we identified kinesin family member 5A (KIF5A) as a novel gene associated with ALS. Interestingly, mutations predominantly in the N-terminal motor domain of KIF5A are causative for two neurodegenerative diseases: hereditary spastic paraplegia (SPG10) and Charcot-Marie-Tooth type 2 (CMT2). In contrast, ALS-associated mutations are primarily located at the C-terminal cargo-binding tail domain and patients harboring loss-of-function mutations displayed an extended survival relative to typical ALS cases. Taken together, these results broaden the phenotype spectrum resulting from mutations in KIF5A and strengthen the role of cytoskeletal defects in the pathogenesis of ALS.
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| 2. |
- Ahlberg, Martina, et al.
(författare)
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Influence of boundaries on magnetic ordering in Fe/V superlattices
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:21, s. 214429-
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Tidskriftsartikel (refereegranskat)abstract
- We study the role of surface boundaries on the magnetic properties of [Fe/V](n) superlattice structures, with n=2-10. Using the magneto-optical Kerr effect and polarized neutron reflectivity measurements, we examine the evolution of both the total and the layer-resolved magnetizations as a function of temperature. By varying n, we observe a large shift in the transition temperatures T-c and a substantial change in the total magnetization critical exponent beta. In particular, the thicker samples exhibit nonuniversal exponent values. By resolving the magnetization as a function of position within the superlattice, we show that this behavior arises from contributions of the surfaces. Furthermore, we attribute the large shift in T-c to long-ranged interactions present in the superlattice.
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| 3. |
- Bergman, Anders, 1978-, et al.
(författare)
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Magnon softening in a ferromagnetic monolayer : A first-principles spin dynamics study
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:14, s. 144416-
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Tidskriftsartikel (refereegranskat)abstract
- We study the Fe/W(110) monolayer system through a combination of first-principles calculations and atomistic spin dynamics simulations. We focus on the dispersion of the spin-waves parallel to the [001] direction. Our results compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett. 102, 177206 (2009)] and correctly capture a drastic softening of the magnon spectrum, with respect to bulk bcc Fe. The suggested shortcoming of the itinerant electron model, in particular that given by density functional theory, is refuted. We also demonstrate that finite-temperature effects are significant, and that atomistic spin dynamics simulations represent a powerful tool with which to include these.
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| 4. |
- Bergqvist, Lars, et al.
(författare)
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Atomistic spin dynamics of low-dimensional magnets
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the magnetic properties of a range of low-dimensional ferromagnets using a combination of first-principles calculations and atomistic spin dynamics simulations. This approach allows us to evaluate the ground state and finite temperature properties of experimentally well characterized systems such as Co/Cu(111), Co/Cu(001), Fe/Cu(001) and Fe/W(110), for different thicknesses of the magnetic layer. We compare our calculated spin wave spectra with experimental data available in the literature, and find a good quantitative agreement. We also predict magnon spectra for systems for which no experimental data exist at the moment, and estimate the role of temperature effects.
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| 5. |
- Bhattacharjee, Satadeep, et al.
(författare)
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Theoretical Analysis of Inertia-like Switching in Magnets : Applications to a Synthetic Antiferromagnet
- 2012
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Ingår i: Physical Review X. - 2160-3308. ; 2:1, s. 011013-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetization dynamics of a synthetic antiferromagnet subjected to a short-magnetic-field pulse has been studied by using a combination of first principles calculations and atomistic spin-dynamics simulations. We observe switching phenomena on the time scale of tens of picoseconds, and inertia-like behavior in the magnetization dynamics. We explain the latter in terms of a dynamic redistribution of magnetic energy from the applied-field pulse to other possible energy terms, such as the exchange interaction and the magnetic anisotropy, without invoking concepts such as the inertia of an antiferro-magnetic vector. We also demonstrate that such dynamics can also be observed in a ferromagnetic material where the incident-field pulse pumps energy to the magnetic anisotropy.
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| 6. |
- Bramwell, Steven T., et al.
(författare)
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Phase order in superfluid helium films
- 2015
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 112:5
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Tidskriftsartikel (refereegranskat)abstract
- Classic experimental data on helium films are transformed to estimate a finite-size phase order parameter that measures the thermal degradation of the condensate fraction in the two-dimensional superfluid. The order parameter is found to evolve thermally with the exponent beta = 3 pi(2)/128, a characteristic, in analogous magnetic systems, of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition. Universal scaling near the BKT fixed point generates a collapse of experimental data on helium and ferromagnetic films, and implies new experiments and theoretical protocols to explore the phase order. These results give a striking example of experimental finite-size scaling in a critical system that is broadly relevant to two-dimensional Bose fluids. This paper is dedicated to the memory of our friend and colleague Maxime Clusel, with whom we enjoyed many stimulating discussions on related topics.
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| 7. |
- Etz, Corina, et al.
(författare)
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Atomistic spin dynamics and surface magnons
- 2015
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 27:24
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Forskningsöversikt (refereegranskat)abstract
- Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya vectors.
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| 8. |
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| 9. |
- Kapaklis, Vassilios, et al.
(författare)
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Melting artificial spin ice
- 2012
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 14, s. 035009-
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Tidskriftsartikel (refereegranskat)abstract
- Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Here we demonstrate a magnetic phase transition in an artificial square spin ice and use the symmetry of the lattice to verify the presence of excitations far below the ordering temperature. We do this by measuring the temperature dependent magnetisation in different principal directions and comparing with simulations of idealised statistical mechanical models. Our results confirm a dynamical pre-melting of the artificial spin ice structure at a temperature well below the intrinsic ordering temperature of the island material. We thus create a spin ice array that has real thermal dynamics of the artificial spins over an extended temperature range.
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| 10. |
- Kenna, Kevin P., et al.
(författare)
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NEK1 variants confer susceptibility to amyotrophic lateral sclerosis
- 2016
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 48:9, s. 1037-1042
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Tidskriftsartikel (refereegranskat)abstract
- To identify genetic factors contributing to amyotrophic lateral sclerosis (ALS), we conducted whole-exome analyses of 1,022 index familial ALS (FALS) cases and 7,315 controls. In a new screening strategy, we performed gene-burden analyses trained with established ALS genes and identified a significant association between loss-of-function (LOF) NEK1 variants and FALS risk. Independently, autozygosity mapping for an isolated community in the Netherlands identified a NEK1 p.Arg261 His variant as a candidate risk factor. Replication analyses of sporadic ALS (SALS) cases and independent control cohorts confirmed significant disease association for both p.Arg261 His (10,589 samples analyzed) and NEK1 LOF variants (3,362 samples analyzed). In total, we observed NEK1 risk variants in nearly 3% of ALS cases. NEK1 has been linked to several cellular functions, including cilia formation, DNA-damage response, microtubule stability, neuronal morphology and axonal polarity. Our results provide new and important insights into ALS etiopathogenesis and genetic etiology.
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| 11. |
- Papaioannou, Evangelos Th, et al.
(författare)
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Dimensionality and confinement effects in delta-doped Pd(Fe) layers
- 2010
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 22:23, s. 236004-
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Tidskriftsartikel (refereegranskat)abstract
- We address the dimensionality aspects of the magnetic ordering in delta-doped Pd(Fe) structures. The key property we investigate, via magneto-optic Kerr measurements, is the magnetization induced by iron in palladium, over a wide temperature range 5 K < T < 300 K. The dimensional crossover we observe cannot be rationalized on the basis of structural considerations alone, since we find the dimensionality of the low temperature and of the critical region can differ. We discuss the crossover in terms of the temperature dependence of the magnon modes, giving rise to lower dimensionality at low temperatures.
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| 12. |
- Taroni, Andrea, et al.
(författare)
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Influence of the range of interactions in thin magnetic structures
- 2010
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Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 77:3, s. 367-371
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Tidskriftsartikel (refereegranskat)abstract
- The properties of thin magnetic structures are influenced by many length scales that reflect both generic physics and chemical detail. A striking example is the experimentally determined shift of the critical temperature as a function of film thickness. While all systems experience a pronounced suppression in the transition temperature with decreasing film thickness, the magnitude of this shift cannot be reconciled with established theoretical results. By means of detailed Monte Carlo simulations, we address this discrepancy by investigating a model with long range interactions. The model also captures other features of real thin magnets, such as an almost linear temperature dependence for the surface magnetization. Our results demonstrate that the behavior of thin magnetic structures arises from a competition of length scales dictated by their slab-like geometry, the presence of surface boundaries, and crucially, the range of the interactions present.
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| 13. |
- Taroni, Andrea, et al.
(författare)
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Suppression of Standing Spin Waves in Low-Dimensional Ferromagnets
- 2011
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:3, s. 037202-
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Tidskriftsartikel (refereegranskat)abstract
- We examine the experimental absence of standing spin wave modes in thin magnetic films, by means of atomistic spin dynamics simulations. Using Co on Cu(001) as a model system, we demonstrate that by increasing the number of layers, the optical branches predicted from adiabatic first-principles calculations are strongly suppressed, in agreement with spin-polarized electron energy loss spectroscopy measurements reported in the literature. Our results suggest that a dynamical analysis of the Heisenberg model is sufficient in order to capture the strong damping of the standing modes.
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| 14. |
- Taroni, Andrea, et al.
(författare)
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Universal window for two-dimensional critical exponents
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:27, s. 275233-
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Forskningsöversikt (refereegranskat)abstract
- Two-dimensional condensed matter is realized in increasingly diverse forms that are accessible to experiment and of potential technological value. The properties of these systems are influenced by many length scales and reflect both generic physics and chemical detail. To unify their physical description is therefore a complex and important challenge. Here we investigate the distribution of experimentally estimated critical exponents, beta, that characterize the evolution of the order parameter through the ordering transition. The distribution is found to be bimodal and bounded within a window similar to 0.1 <= beta <= 0.25, facts that are only in partial agreement with the established theory of critical phenomena. In particular, the bounded nature of the distribution is impossible to reconcile with the existing theory for one of the major universality classes of two-dimensional behaviour - the XY model with four-fold crystal field - which predicts a spectrum of non-universal exponents bounded only from below. Through a combination of numerical and renormalization group arguments we resolve the contradiction between theory and experiment and demonstrate how the 'universal window' for critical exponents observed in experiment arises from a competition between marginal operators.
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| 15. |
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| 16. |
- Östman, Erik, et al.
(författare)
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Ising-like behaviour of mesoscopic magnetic chains
- 2018
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 30:36
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate an experimental realization of the short range magnetic order in a one-dimensional Ising chain using fabricated mesospins. We confirm an excellent agreement between the experimental findings and simulations obtained using the original Ising model. In particular, we are able to show that the thermal behaviour of the mesoscopic Ising chain dominates over the thermal behaviour of the individual mesospins themselves, confirming that fabricated mesospins can be viewed as artificial magnetic atoms.
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| 17. |
- Aad, G, et al.
(författare)
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- 2015
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swepub:Mat__t
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