La magnéto-optique s‘impose désormais dans un grand nombre de domaines : les télécommunications, le traitement du signal, les capteurs et le stockage de l’information. Cet article rappelle d’abord l’origine des effets magnéto-optiques. Les constantes magnéto-optiques de matériaux couramment utilisés sont répertoriées. Des matériaux hybrides émergents comme les cristaux magnétophotoniques et les structures magnétoplasmoniques permettent d’intégrer des fonctions nanophotoniques dans des dispositifs miniaturisés. Les propriétés magnétiques de nanostructures artificielles sont couramment testées par magnétométrie et microscopie magnéto-optique.

Cet article présente tout d’abord les spécificités et avantages de la magnéto-optique, ainsi que ses nombreuses applications. Les dispositifs magnéto-optiques utilisés les plus couramment (isolateurs, circulateurs, modulateurs, déflecteurs, pour l’imagerie…) sont décrits. Les progrès en nanosciences (nano-optique, nano-magnétisme, nanomatériaux et nano-structuration) doivent permettre l’intégration de nombreuses fonctions dans des dispositifs miniaturisés reposant sur des disciplines émergentes : la magnéto-photonique et la magnéto-plasmonique. De nouvelles opportunités sont aussi ouvertes en microscopie magnéto-optique appliquée aux sciences des matériaux et à l’étude de systèmes magnétiques nanostructurés destinés, en particulier, à l’électronique de spin.

The motion of elastic interfaces in disordered media is a broad topic relevant to many branches of physics. Field-driven magnetic domain wall motion in ultrathin ferromagnetic Pt/Co/Pt films can be well interpreted within the framework of theories developed to describe elastic interface dynamics in the presence of weak disorder. Indeed, the three theoretically predicted dynamic regimes of creep, depinning, and flow have all been directly evidenced in this model experimental system. We discuss these dynamic regimes and demonstrate how field-driven creep can be controlled not only by temperature and pinning, but also via interactions with magnetic entities located inside or outside the magnetic layer. Consequences of confinement effects in nano-devices are briefly reviewed, as some recent results on domain wall motion driven by an electric current or assisted by an electric field. Finally new theoretical developments and perspectives are discussed. (C) 2013 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

We report on current induced domain wall propagation in a patterned GaMnAs microwire with perpendicular magnetization. An unexpected slowing down of the propagation velocity has been found when the moving domain wall extends over only half of the width of the wire. This slowing down is related to the elongation of a longitudinal wall along the axis of the wire. By using an energy balance argument, the expected theoretical dependence of the velocity change has been calculated and compared with the experimental results. According to this, the energy associated to the longitudinal domain wall should change when a current passes through the wire. These results provide possible evidence of transverse spin diffusion along a longitudinal domain wall.

The field-driven velocity of magnetic domain walls in nanostrips patterned in (Co/Ni) multilayer films with perpendicular anisotropy is studied by magnetooptical microscopy. By applying fields up to 250 mT, two peculiar features are revealed, which are beyond the simple one-dimensional model. First, above wall depinning, a velocity plateau is observed over a 150 mT field range. Then, at large fields, an important increase of velocity occurs. Micromagnetic simulations reproduce this behaviour and underline the nontrivial role of wall structure deformations in the appearance of this complexity.

The aim of this article is to report on preliminary investigations in evaluating a new kind of focused ion beam (FIB) instrument realized by coupling an advanced FIB “nanowriter” with a compact electron beam ion trap. The authors demonstrate the possibility to produce noble gas ion beams (He, Ar, Xe, and Kr) in a FIB machine using an electron beam ion trap. Preliminary results obtained using highly charged ions as projectiles are presented.

Thermally assisted motion of magnetic domain wall under spin torque is studied theoretically. It is shown that the wall velocity v depends exponentially on the spin current, Is, below the threshold value, in the same way as in a thermally activated motion driven by a force. A significant property of the spin torque driven case at low temperature is that the linear term in spin current is universal, i.e., Inv∼πℏ∕2e(Is∕kBT). This behavior, which is independent of pinning and material constants, could be used to confirm experimentally the spin torque as the driving mechanism.

Decisive advances in the field of nanosciences and nanotechnologies are intimately related to the development of new instruments and of related writing schemes and methodologies. Therefore we have recently proposed the exploitation of the nano-structuring potential of a highly focused ion beam (FIB) as a tool, to overcome intrinsic limitations of current nano-fabrication techniques and to allow innovative patterning schemes that are urgently needed in many nanoscience challenges. In this work, we will first detail a very high-resolution FIB instrument we have developed specifically to meet these nano-fabrication requirements. Then we will introduce and illustrate an advanced FIB processing scheme that is the fabrication of artificial nanopores.

We performed magnetic-field-induced experiments on micron-sized patterned Co70.4Fe4.6Si15B10 square thin-film elements with in-plane magnetic anisotropy by magneto-optical scanning near-field optical microscopy (MO-SNOM) with a spatial resolution better than 200 nm. Markedly different local hysteresis loops (LHLs) were measured on selected positions in one element. Some LHLs presented an unusual shape intrinsic of local magnetic-field-induced process. Comparison of the MO-SNOM imaging results with high-resolution far-field Kerr microscopy has confirmed the local character of the MO-SNOM measurements. This has also helped us to understand the unusual LHLs shapes as related to the field-induced rearrangement of the domain structure within the square element during the magnetization process. The magnetic structure in small field is well described by two overlapping four-domain flux-closure configurations that are well modeled by micromagnetic calculations.

Controlled and reproducible fabrication of nano-structured materials will constitute one of the main industrial challenges for the next 10 years. To overcome the severe limitations of existing nano-fabrication techniques, we have developed and improved the ultimate usable resolution of an innovative focused ion beam instrument (FIB). In this work we demonstrate that FIB techniques allow quite simple, direct, clean and reproducible material nano-structuring close to or below the 10 nm level.

The macroscopic and microscopic theory of Linear and Non-Linear Magneto- optical (LMO and NLMO) effects are first summarised. The specificity of MO effects for measuring the vectorial components of the magnetisation are underlined and the time and spatial resolution emphasised in the case of ultrathin magnetic film structures. NLMO’s allows checking the surface and interface magnetism while in-depth magnetisation measurements may be performed by LMO’s. Several up to date problems in thin film magnetism have been solved by MO’s, such as the domain wall dynamics in the Pt/Co/Pt ultrathin thin film structure and the magnetisation reversal dynamics of magnetically non-coupled or coupled small dot arrays.

The in-plane (transverse) H∥ field-induced magnetization reversal process in a polycrystalline Au/Co/Au ultrathin magnetic film structure with strong perpendicular anisotropy has been studied. Faraday rotation microscopy shows that the domain structure, initially prepared under an H⊥ field, is not influenced under H∥. Only the value of the net perpendicular magnetization inside the domains is reduced. Our data are described in the frame of a simple model which assumes that the sample is composed of nanometer-sized uncoupled atomic terraces (patches) with different local anisotropies. The limits of our model are discussed.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Magnetically textured y-Fe2O3 nanoparticles in a silica gel matrix: structural and magnetic properties Florian Bentivegna, J. Ferre, M. Nyvlt, J.P. Jamet, Dominique Imhoff, Michael Canva, Alain Brun, P. Veillet, Š Višňovský, Frédéric Chaput, et al.