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Trabajo presentado en la 62nd Annual Conference on Magnetism and Magnetic Materials, celebrada en Pittsburgh (Alabama, Estados Unidos), del 6 al 9 de noviembre de 2017

Trabajo presentado en el INTERMAG Europe, celebrado en Dublín (Irlanda), del 24 al 28 de abril de 2017, In recent years, Spin Orbit interaction as a source of spin current has been widely used through the physics of Spin Hall Effect (SHE) or that of Rashba effect. The peculiar symmetry of SHE allows creating a spin accumulation at the interface between a spin-orbit metal and a magnetic insulator that could lead to a net pure spin current flowing from the metal into the insulator. This spin current will induce a torque on the magnetization and eventually could drive it into steady motion. The magnetization dynamics can be detected electrically on the metal using the inverse spin Hall effect (ISHE). As a ferromagnetic insulator with a very low Gilbert damping, Yttrium Iron Garnet (YIG) is a very promising candidate to investigate pure spin current phenomena [1.2]. In a previous study, we have been able to observe auto-oscillation induced by SHE torques in 20 nm thick YIG disks [3]. In this work, we have gone towards 1D microstructure to observe the effect of SHE torques on this extended system that can be important for potential magnonics application [4]. The samples used are 1 ¿m wide YIG (20 nm)\Pt (7 nm) stripes that have been lithographically defined. DC electrical contacts separated by 80 ¿m are also defined on the top of the stripes to inject ac-current and detect the ISHE voltage. A lock-in detection technique is used to remove the Ohm¿s law contribution and we measure simultaneously two identical stripes in parallel with a bridge measurement configuration to observe any SHE torques signal in the second harmonic voltage (Fig. 1(a)). Due to Joule heating by passing current in the Pt layer, a spin Seebeck effect (SSE) signal can also be detected in the ISHE voltage [5,6]. The angular dependence of the second harmonic voltage shows mostly a 180° period signal in the film plane in agreement with the SHE (ISHE) symmetry of the injected (detected) spin current in the measurement configuration (Fig. 1(b)). A minor contribution also appears showing a dependence in agreement with the SSE signal where only the direction of the YIG magnetization is relevant. Thanks to symmetry consideration, we can disentangle any thermal effects from torques effects and notice a much larger signal coming from SHE torques. When we reach the threshold current for the onset of auto-oscillations that was observed by ¿-BLS on the same stripes [7], we obtain an abrupt decrease in the amplitude of the SHE voltage. We attribute this behavior to strong non-linear mode coupling in the excited magnetization dynamic. The interplay between thermal and coherent modes excited by SHE torques will be discussed. This study shows the excitation of YIG dynamics by SHE torques and its electrical detection via ISHE, separately from the SSE signal, in a YIG/Pt stripe.

Trabajo presentado en el INTERMAG Europe, celebrado en Dublín (Irlanda), del 24 al 28 de abril de 2017

Trabajo presentado en la 61st Annual Conference on Magnetism and Magnetic Materials, celebrada en New Orleans (Lousiana, EE.UU), del 31 de octubre al 4 de noviembre de 2016

Trabajo presentado en la 61st Annual Conference on Magnetism and Magnetic Materials, celebrada en New Orleans (Lousiana, EE.UU), del 31 de octubre al 4 de noviembre de 2016

Trabajo presentado en el 17ème colloque Louis Néel, celebrado en Saint Dié des Vosges (Francia), del 29 de marzo al 1 de abril de 2016, Une nouvelle direction en spintronique, appelée spin-orbitronique, vise à exploiter des effets liés au couplage spin-orbite (SOC) i.e. effet Hall de spin (SHE) ou effet Edelstein-Rashba (ERE) au lieu de l¿interaction d¿échange pour générer, détecter et manipuler des courants de spin. Cela ouvre la voie pour le développement de dispositifs spintroniques basés non seulement sur des matériaux non magnétiques mais aussi qui ne nécessitent plus un champ magnétique pour fonctionner. De plus, et c¿est l¿objectif principal de cette étude, cette approche permet d¿ouvrir le champ de la spintronique à des matériaux isolants magnétiques qui présentent intrinsèquement d¿excellentes propriétés dynamiques et dont le représentant le plus connu est le grenat d¿Yttrium (YIG). Dans cette étude, nous montrons de façon non ambiguë la mise en précession de l¿aimantation d¿une couche mince de YIG (20 nm) dans des microstructures de YIG\Pt. Cette dynamique cohérente de l¿aimantation est induite en faisant passer un courant électrique dans la couche de Pt (le YIG étant un parfait isolant électrique). Nous attribuons nos observations à un couple de transfert de spin induit sur l¿aimantation du YIG par l¿accumulation de spin dans le Pt à l¿interface YIG\Pt. Nous démontrons que cette accumulation de spin a la symétrie attendue du SHE existant dans le Pt.

We study translational, breathing and twisting resonant modes of transverse magnetic domain walls pinned at notches in ferromagnetic nanostrips. We demonstrate that a mode's sensitivity to notches depends strongly on the characteristics of that particular resonance. For example, the frequencies of modes involving lateral motion of the wall are the ones which are most sensitive to changes in the notch intrusion depth (especially at the narrower, more strongly confined end of the domain wall). In contrast, the breathing mode, whose dynamics are concentrated away from the notches is relatively insensitive to changes in the notches' sizes. We also demonstrate a sharp drop in the translational mode's frequency towards zero when approaching depinning which is found, using a harmonic oscillator model, to be consistent with a reduction in the local slope of the notch-induced confining potential at its edge., 11 pages, 10 figures, additional data and analysis

Trabajo presentado en la 61st Annual Conference on Magnetism and Magnetic Materials, celebrada en New Orleans (Lousiana, EE.UU), del 31 de octubre al 4 de noviembre de 2016

International audience; A powerful imaging technique based on femtosecond time-resolved measurements with a high dynamic range, commercial CCD camera is presented. Ultrafast phenomena induced by a femtosecond laser pump are visualized through the lock-in type acquisition of images recorded by a femtosecond laser probe. This technique allows time-resolved measurements of laser excited phenomena at multiple probe wavelengths (spectrometer mode) or conventional imaging of the sample surface (imaging mode). Two examples based on time-resolved imaging of the sample surface are presented. First, we follow the non-linear reshaping of an acoustic strain pulse in a hybrid gold/cobalt layer at ambient temperature in a sequence of images. Second, we examine time-resolved images of transient thermal heating in graphene samples where we observe heat dissipation as fast as one picosecond which neither depends on the number of layers nor the shape of the graphene sample. A wealth of adaptations of the presented technique can be considered such as imaging of ultrasonic echoes in biological samples (ultrasonic microscopy with resolution down to tens of nanometer).