Spintronique, de la magnétorésistance géante aux Skyrmions magnétiques et isolants topologiques

International audienceThis article aims at giving a general presentation of spintronics, an important field of research developing today along many new directions in physics of condensed matter. We tried to present simply the physical phenomena involved in spintronics – no equations but many schematics. We also described the applications of spintronics, those of today and those expected to have an important impact on the next developments of the information and communication technologies.Cet article se veut une présentation générale de la spintronique. C’est aujourd’hui un important domaine de recherche qui se développe sur de nombreux nouveaux axes de la physique de la matière condensée. Nous avons voulu présenter simplement les phénomènes physiques impliqués dans la spintronique – sans équations mais avec de nombreux schémas. Nous décrivons aussi les applications de la spintronique, celles d’aujourd’hui et celles dont l’on attend un impact important sur les prochains développements des technologies de l’information et de la communication

Spintronics, from giant magnetoresistance to magnetic skyrmions and topological insulators

This article aims at giving a general presentation of spintronics, an important field of research developing today along many new directions in physics of condensed matter. We tried to present simply the physical phenomena involved in spintronics -- no equations but many schematics. We also described the applications of spintronics, those of today and those expected to have an important impact on the next developments of the information and communication technologies

Capacités variables utilisant le blocage de Coulomb (Application aux composants RF)

La poursuite de la diminution des puissances requises dans les composants électroniques a poussé à une miniaturisation à l'extrême des composants existants. De nouveaux phénomènes physiques tel que le blocage de Coulomb apparaissent, permettant de nouvelles fonctionnalités. Les composants RF agiles en fréquence utilisent des capacités variables commandées en tension pour changer leur fréquence de fonctionnement. Ce mémoire est dédié à l'étude d'un dispositif de capacité variable utilisant le blocage de Coulomb pour modifier la charge dans un plan de nano-îlots insérés dans une matrice diélectrique entre deux électrodes, changeant ainsi la capacité différentielle. Ce système ayant, lors de travaux antérieurs, prouvé expérimentalement son fonctionnement, ce travail a conduit à la détermination d'un modèle décrivant les interactions entre les conducteurs et de l'impact de celles-ci sur le transport électronique. Ainsi, un circuit équivalent au dispositif, et reposant sur les paramètres de fabrication (épaisseurs et constantes diélectriques, ), a été défini et validé par comparaison à des mesures expérimentales précédemment obtenues sur ces dispositifs.The never ending quest in reduction of power consumption and increase in components density has led to downscale existing components. As a consequence, the appearance of new physical phenomena, such as Coulomb blockade, leads to new electronic functionalities. Tuneable RF devices use voltage driven variable capacitances in order to manage the change of their operating frequency. This work is dedicated to the study of a variable capacitance device based on Coulomb blockade so as to modify the charge in a plane of nano-islands embedded in a dielectric matrix sandwiched between two electrodes, what changes the differential capacitance. Following a former study which has experimentally proved the working of this system, this work has led to the development of a model describing interactions between conductors and their impact on the electronic transport. Then, a device-equivalent circuit that only needs fabrication parameters in input (thicknesses and dielectric constants of the insulating barriers, ) has been defined and validated by comparison to formerly obtained experimental measurements on those devices.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Design of magnetic concentrators for high sensitivity anisotropic magnetoresistor devices

International audienceIn this work, a very promising shape of magnetic concentrators taking advantage of the symmetrical flux leakage of Mn-Zn ferrite magnetic cores is presented. This configuration consists of two ferromagnetic rods separated by two air gaps allowing to place anisotropic magnetoresistance sensors in the core axis. Results from three-dimensional finite elements modeling are presented. We show that an appropriate shape optimization of core extremities enables to improve significantly the amplification factor without any increase in length

Linear and quadratic magneto-optical measurements of the spin reorientation in epitaxial Fe films on MgO

We have undertaken a detailed study by magneto-optical techniques of in-plane magnetization reversal behaviour in epitaxial Fe films grown by MBE on (10 0) oriented MgO substrate. We measure M---H loops for both orthogonal in-plane magnetization components Mt (component parallel to the magnetic field) and Mt (component perpendicular to the field) and for various orientations of the magnetic field with respect to the crystalline axis. These measurements show the classical four-fold cubic anisotropy for large Fe film thickness and confirm the appearance of weak uniaxial in-plane anisotropy superimposed for thinner films (t = 20 Å). We have demonstrated the appearance of strong asymmetrical hysteresis loop for p-polarized incident light. We explain this behaviour as the mixing of transverse magnetization contribution to the longitudinal magnetization measurements on the basis of quadratic magneto-optical effects. The calculation of these effects based on eigenmode propagation in anisotropic layered media are developed by including the second-order magneto-optical terms in the permittivity tensor characteristic of a cubic crystal. The second-order reflection coefficients are discussed in the case of the normal incidence of the laser beam and for the magnetic field along the hard axis of the Fe film

Strong uniaxial magnetic anisotropy of nanostripes obtained by cutting thin epitaxial Fe layer using the atomic saw method

We have applied the "atomic saw" method developed on semiconductor heterostructures to cut thin epitaxial Fe films deposited on (001) MgO substrate into Fe nanostripes. This method is based on dislocation slipping. We have controlled the slip along the (110) MgO planes and obtained Fe stripes along the [110] direction. We present the magnetic study of 2- and 5-nm-thick Fe films which have been cut by this method, with a deformation up to 8%. The surface of the deformed film, studied by atomic force microscopy, is characterized by regular steps, a few nm high, and from 50 nm to 2 µm wide, depending on the slipping plane density. Strong uniaxial magnetic anisotropy has been observed by magneto-optical measurements. Surprisingly, the easy magnetic axis is perpendicular to the nanostripes. Various possible mechanisms are discussed. However, it results probably in the relaxation of the elastic strain field at the Fe/MgO interface

Giant magnetoresistance of (001)fe/(001)cr magnetic superlattices

We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecular-beam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with tCr=9 Å, at T =4.2 K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers

Giant magnetoresistance of (001)fe/(001)cr magnetic superlattices

We have studied the magnetoresistance of (001)Fe/(001)Cr superlattices prepared by molecular-beam epitaxy. A huge magnetoresistance is found in superlattices with thin Cr layers: For example, with tCr=9 Å, at T =4.2 K, the resistivity is lowered by almost a factor of 2 in a magnetic field of 2 T. We ascribe this giant magnetoresistance to spin-dependent transmission of the conduction electrons between Fe layers through Cr layers

Uniaxial magnetic anisotropy of thin epitaxial Fe films nanostructured by the atomic saw method

The ‘atomic saw' method, initially developed for semiconductor heterostructures, has been successfully used to cut an iron thin film, epitaxially grown onto a (0 0 1)MgO substrate, into stripes (1 μm–100 nm large and 8–1 nm high) or boxes (whose in-plane dimension ranges from 1 to 3 μm). A structural analysis by atomic force microscopy (AFM) of the created magnetic nanostructures demonstrates the efficiency of this simple method and reveals that their geometries are controlled by the choice of the plastic strain. Magneto-optical study of films cut into stripes exhibit a surprisingly strong uniaxial magnetic anisotropy with the in-plane easy axis perpendicular to the stripes. This strong anisotropy (ranging from 8×105 to 14×105 erg/cm3) can be explained by a uniaxial relaxation of the elastic strain field. Magnetic studies on boxes reveal that the cubic magnetocrystalline energy is recovered since, in this case, the ‘atomic saw' method acts in a biaxial way in the layer plane. Magnetization reversal, contrary to the case of a continuous epitaxial Fe film characterized by rapid displacement of 180 and 90 domain walls, is now governed by nucleation process