arXiv subjects

Stanislas Rohart

Publications and source records attributed to Stanislas Rohart.

24 records · Page 2Linked to original sources

arXiv2012

Dynamics of Dzyaloshinskii domain walls in ultrathin magnetic films

We explore a new type of domain wall structure in ultrathin films with perpendicular anisotropy, that is influenced by the Dzyaloshinskii-Moriya interaction due to the adjacent layers. This study is performed by numerical and analytical micromagnetics. We show that these walls can behave like Neel walls with very high stability, moving in stationary conditions at large velocities under large fields. We discuss the relevance of such walls, that we propose to call Dzyaloshinskii domain walls, for current-driven domain wall motion under the spin Hall effect.

cond-mat.mes-hall↗

arXiv2011

Chemical order and size effects on the magnetic anisotropy of FePt and CoPt nanoparticles

We investigate the consequence of the dimension reduction on the magnetic anisotropy of FePt and CoPt nanoparticles. Using an extension of the magnetic anisotropy model of Néel, we show that, due to a statistical finite size effect, chemically disordered clusters can display a magnetic anisotropy energy (MAE) as high as 0.5\times10^6 J/m3, more than one order of magnitude higher than the bulk MAE. Concerning L10 ordered clusters, we show that the surface induces a reduction of the MAE as compared to the bulk, due to the symmetry breaking at the cluster surface, which modifies the chemical order.

cond-mat.mes-hall↗

arXiv2011

On the magnetization textures in NiPd nanostructures

We have observed peculiar magnetization textures in Ni$_{80}$Pd$_{20}$ nanostructures using three different imaging techniques: magnetic force microscopy, photoemission electron microscopy under polarized X-ray absorption, and scanning electron microscopy with polarization analysis. The appearances of diamond-like domains with strong lateral charges and of weak stripe structures bring into evidence the presence of both a transverse and a perpendicular anisotropy in these nanostrips. This anisotropy is seen to reinforce as temperature decreases, as testified by a simplified domain structure at 150 K. A thermal stress relaxation model is proposed to account for these observations. Elastic calculations coupled to micromagnetic simulations support qualitatively this model.

cond-mat.mes-hall↗

arXiv2010

Domain wall structure in magnetic bilayers with perpendicular anisotropy

We study the magnetic domain wall structure in magnetic bilayers (two ultrathin ferromagnetic layers separated by a non magnetic spacer) with perpendicular magnetization. Combining magnetic force and ballistic electron emission microscopies, we are able to reveal the details of the magnetic structure of the wall with a high spatial accuracy. In these layers, we show that the classical Bloch wall observed in single layers transforms into superposed Néel walls due to the magnetic coupling between the ferromagnetic layers. Quantitative agreement with micromagnetic calculations is achieved.

cond-mat.mes-hall↗

arXiv2006

Magnetic anisotropy of $Co_x Pt_{1-x}$ clusters embedded in matrix: Influences of the cluster chemical composition and the matrix nature

We report on the magnetic properties of Co$\_x$Pt$\_{1-x}$ clusters embedded in various matrices. Using a careful analysis of magnetization curves and ZFC susceptibility measurements, we determine the clusters magnetic anisotropy energy (MAE) and separate the surface and volume contributions. By comparing different chemical compositions, we show that a small amount of Pt (15%) induces an important increase in the volume anisotropy with respect to pure Co clusters, even in chemically disordered fcc clusters. Comparing the measurements of clusters embedded in Nb and MgO matrices, we show that the oxide matrix induces an important increase of the surface MAE attributed to the formation of an antiferromagnetic CoO shell around the clusters.

cond-mat.mtrl-sci↗

arXiv2004

Atomistic mechanisms for the ordered growth of Co nano-dots on Au(788): comparison of VT-STM experiments and multi-scaled calculations

Hetero-epitaxial growth on a strain-relief vicinal patterned substrate has revealed unprecedented 2D long range ordered growth of uniform cobalt nanostructures. The morphology of a Co sub-monolayer deposit on a Au(111) reconstructed vicinal surface is analyzed by Variable Temperature Scanning Tunneling Microscopy (VT-STM) experiments. A rectangular array of nano-dots (3.8 nm x 7.2 nm) is found for a particularly large deposit temperature range lying from 60 K to 300 K. Although the nanodot lattice is stable at room temperature, this paper focus on the early stage of ordered nucleation and growth at temperatures between 35 K and 480 K. The atomistic mechanisms leading to the nanodots array are elucidated by comparing statistical analysis of VT-STM images with multi-scaled numerical calculations combining both Molecular Dynamics for the quantitative determination of the activation energies for the atomic motion and the Kinetic Monte Carlo method for the simulations of the mesoscopic time and scale evolution of the Co submonolayer.

cond-mat.mtrl-sci↗