arXiv subjects

N. Rougemaille

Publications and source records attributed to N. Rougemaille.

24 records · Page 2Linked to original sources

arXiv2014

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.

cond-mat.mes-hall↗

arXiv2014

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.

cond-mat.mes-hall↗

arXiv2011

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.

cond-mat.mes-hall↗

arXiv2010

3D magnetization profile and multi-axes exchange bias in Co antidot arrays

Cu/Co/Cu trilayers have been deposited on nanoporous alumina membranes. Magnetic properties of the resulting Co antidot arrays are investigated using SQUID magnetometry. Hysteresis loops of these arrays show two-step magnetization reversal. In addition, exchange bias is observed, whether the cooling field is applied within or perpendicular to the surface plane. In the former case, the exchange bias changes sign close to the blocking temperature, and becomes positive. We attribute these effects to the local, crescent shape of the Co films, induced by the surface morphology of the alumina membranes. This morphology leads to a three-dimensional magnetization distribution at the nanoscale.

cond-mat.mtrl-sci↗

arXiv2008

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.

cond-mat.mtrl-sci↗

arXiv2007

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.

cond-mat.mtrl-sci↗