91 research outputs found
Chiral nature of magnetic monopoles in artificial spin ice
Micromagnetic properties of monopoles in artificial kagome spin ice systems
are investigated using numerical simulations. We show that micromagnetics
brings additional complexity into the physics of these monopoles that is, by
essence, absent in spin models: besides a fractionalized classical magnetic
charge, monopoles in the artificial kagome ice are chiral at remanence. Our
simulations predict that the chirality of these monopoles can be controlled
without altering their charge state. This chirality breaks the vertex symmetry
and triggers a directional motion of the monopole under an applied magnetic
field. Our results also show that the choice of the geometrical features of the
lattice can be used to turn on and off this chirality, thus allowing the
investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure
Non-universality of artificial frustrated spin systems
Magnetic frustration effects in artificial kagome arrays of nanomagnets with
out-of-plane magnetization are investigated using Magnetic Force Microscopy and
Monte Carlo simulations. Experimental and theoretical results are compared to
those found for the artificial kagome spin ice, in which the nanomagnets have
in-plane magnetization. In contrast with what has been recently reported, we
demonstrate that long range (i.e. beyond nearest-neighbors) dipolar
interactions between the nanomagnets cannot be neglected when describing the
magnetic configurations observed after demagnetizing the arrays using a field
protocol. As a consequence, there are clear limits to any universality in the
behavior of these two artificial frustrated spin systems. We provide arguments
to explain why these two systems show striking similarities at first sight in
the development of pairwise spin correlations.Comment: 7 pages, 6 figure
360 degree domain wall generation in the soft layer of magnetic tunnel junctions
High spatial resolution X-ray photo-emission electron microscopy technique
has been used to study the influence of the dipolar coupling taking place
between the NiFe and the Co ferromagnetic electrodes of micron sized,
elliptical shaped magnetic tunnel junctions. The chemical selectivity of this
technique allows to observe independently the magnetic domain structure in each
ferromagnetic electrode. The combination of this powerful imaging technique
with micromagnetic simulations allows to evidence that a 360 degree domain wall
can be stabilized in the NiFe soft layer. In this letter, we discuss the origin
and the formation conditions of those 360 degree domain walls evidenced
experimentally and numerically
Indirect localization of a magnetic domain wall mediated by quasi walls
International audienceThe manipulation of magnetic domain walls in thin films and nanostructures opens new opportunities for fundamental and applied research. But controlling reliably the position of a moving domain wall still remains challenging. So far, most of the studies aimed at understanding the physics of pinning and depinning processes in the magnetic layer in which the wall moves (active layer). In these studies, the role of other magnetic layers in the stack has been often ignored. Here, we report an indirect localization process of 180° domain walls that occurs in magnetic tunnel junctions, commonly used in spintronics. Combining Scanning Transmission X-Ray Microscopy and micromagnetic simulations, magnetic configurations in both layers are resolved. When nucleating a 180° domain wall in the active layer, a quasi wall is created in the reference layer, atop the wall. The wall and its quasi wall must then be moved or positioned together, as a unique object. As a mutual effect, a localized change of the magnetic properties in the reference layer induces a localized quasi wall in the active layer. The two types of quasi walls are shown to be responsible for an indirect localization process of the 180° domain wall in the active layer
Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice
Magnetic frustration effects in artificial kagome arrays of nanomagnets are
investigated using x-ray photoemission electron microscopy and Monte Carlo
simulations. Spin configurations of demagnetized networks reveal unambiguous
signatures of long range, dipolar interaction between the nanomagnets. As soon
as the system enters the spin ice manifold, the kagome dipolar spin ice model
captures the observed physics, while the short range kagome spin ice model
fails.Comment: 4 pages, 4 figures, 1 tabl
Energy levels of interacting curved nano-magnets in a frustrated geometry: increasing accuracy when using finite difference methods
The accuracy of finite difference methods is related to the mesh choice and
cell size. Concerning the micromagnetism of nano-objects, we show here that
discretization issues can drastically affect the symmetry of the problem and
therefore the resulting computed properties of lattices of interacting curved
nanomagnets. In this paper, we detail these effects for the multiaxe kagome
lattice. Using the Oommf finite difference method, we propose an alternative
way of discretizing the nanomagnet shape via a variable moment per cell scheme.
This method is shown to be efficient in reducing discretization effects.Comment: 4 pages, 5 figure
Size distribution of magnetic charge domains in thermally activated but out-of-equilibrium artificial spin ice
International audienceA crystal of emerging magnetic charges is expected in the phase diagram of the dipolar kagome spin ice. An observation of charge crystallites in thermally demagnetized artificial spin ice arrays has been recently reported by S. Zhang and coworkers and explained through the thermodynamics of the system as it approaches a charge-ordered state. Following a similar approach, we have generated a partial order of magnetic charges in an artificial kagome spin ice lattice made out of ferrimagnetic material having a Curie temperature of 475 K. A statistical study of the size of the charge domains reveals an unconventional sawtooth distribution. This distribution is in disagreement with the predictions of the thermodynamic model and is shown to be a signature of the kinetic process governing the remagnetization
Exchange-induced frustration in Fe/NiO multilayers
Using spin-polarized low-energy electron microscopy to study magnetization in
epitaxial layered systems, we found that the area vs perimeter relationship of
magnetic domains in the top Fe layers of Fe/NiO/Fe(100) structures follows a
power-law distribution, with very small magnetic domain cutoff radius (about 40
nm) and domain wall thickness. This unusual magnetic microstructure can be
understood as resulting from the competition between antiferromagnetic and
ferromagnetic exchange interactions at the Fe/NiO interfaces, rather than from
mechanisms involving the anisotropy and dipolar forces that govern length
scales in conventional magnetic domain structures. Statistical analysis of our
measurements validates a micromagnetic model that accounts for this interfacial
exchange coupling.Comment: 15 pages, 2 figure
Reversible temperature-driven domain transition in bistable Fe magnetic nanostrips grown on Ru(0001)
© 2015 American Physical Society. High-aspect-ratio Fe nanostrips are studied with real-space micromagnetic imaging methods. We experimentally demonstrate reversible switching from essentially homogeneous single-domain states at room temperature to multidomain diamond states at elevated temperature. This temperature-dependent magnetic bistability can be understood and modeled by accounting for the temperature dependence of the magnetocrystalline, shape, and magnetoelastic anisotropies. These results show how the transition temperature between two magnetic domain states can be tailored by controlling epitaxial strain and particle geometry, which may generate new opportunities for magnetic memory and logic device design.Peer Reviewe
Arginine methylation of REF/ALY promotes efficient handover of mRNA to TAP/NXF1
The REF/ALY mRNA export adaptor binds TAP/NXF1 via an arginine-rich region, which overlaps with its RNA-binding domain. When TAP binds a REF:RNA complex, it triggers transfer of the RNA from REF to TAP. Here, we have examined the effects of arginine methylation on the activities of the REF protein in mRNA export. We have mapped the arginine methylation sites of REF using mass spectrometry and find that several arginines within the TAP and RNA binding domains are methylated in vivo. However, arginine methylation has no effect on the REF:TAP interaction. Instead, arginine methylation reduces the RNA-binding activity of REF in vitro and in vivo. The reduced RNA-binding activity of REF in its methylated state is essential for efficient displacement of RNA from REF by TAP in vivo. Therefore, arginine methylation fine-tunes the RNA-binding activity of REF such that the RNA–protein interaction can be readily disrupted by export factors further down the pathway
- …