Grenat de fer et d'yttrium | EPFL Graph Search

Le grenat de fer et d'yttrium, ou YIG pour Yttrium Iron Garnet, est un composé chimique de formule , c'est-à-dire . Il est également connu sous les noms de grenat de ferrite et d'yttrium, d'oxyde de fer et d'yttrium et d'oxyde d'yttrium et de fer, ces deux dernières appellations étant généralement associées aux formes pulvérulentes. C'est un grenat de synthèse qui n'a pas été observé dans le milieu naturel. Il s'agit d'un isolant ferrimagnétique ayant une température de Curie de . Dans le YIG, les cinq ions ferriques Fe occupent deux sites octaédriques et trois sites tétraédriques, tandis que les ions d'yttrium Y sont coordonnés à huit atomes d'oxygène. Les ions ferriques des deux sites de coordination présentent des spins différents, d'où leurs propriétés magnétiques. Il possible d'obtenir des matériaux aux propriétés magnétiques intéressantes en substituants certains atomes de la structure avec des terres rares. Le YIG présente une constan

Effect of Heat Current on Magnetization Dynamics in Magnetic Insulators and Nanostructures

Francesco Antonio Vetrò

The term "spin caloritronics" defines a novel branch of spintronics that focuses on the interplay between electron spins with heat currents. In the frame of this research area, this thesis is aimed at investigating the effect of a heat current on magnetization dynamics in two different typologies of systems and materials: magnetic insulators and metallic nanostructures. In the first case we conduct studies on yttrium iron garnet (YIG) samples subjected to a temperature gradient. The irreversible thermodynamics of a continuous medium with magnetic dipoles predicts that a thermal gradient across a YIG slab, in the presence of magnetization waves, produces a magnetic field that is the magnetic analog of the well known Seebeck effect. This thermally induced field can influence the time evolution of the magnetization, in such a way that it is possible to modulate the relaxation of the precession when applying a heat current. We found evidence for such a magnetic Seebeck effect (MSE) by conducting transmission measurements in a thin slab of YIG subjected to an in-plane temperature gradient. We showed how the MSE can modulate the magnetic damping depending on the direction of the propagating magnetostatic modes with respect to the orientation of the temperature gradient. In the second part of the thesis we focus our investigation on metallic nanostructures subjected to a heat current. In a metal, the three-current model (current of entropy, of spin up and spin down electrons) predicts that a heat current induces a spin current which will then influence the magnetization dynamics like a charge-driven spin current would. Hence, we explore what has been called Thermal Spin Torque in electrodeposited Co / Cu / Co asymmetric spin valves placed in the middle of copper nanowires. These samples are fabricated by conventional electrodeposition technique in porous polycarbonate membranes using an original method that allows high frequency electrical measurements. We used a modulated laser to investigate the effect of a temperature gradient. We observed a heat-driven spin torque by measuring electrically the quasi-static magnetic response of a spin valve when subjected to the heat current, generated by two laser diodes heating the electrical contact at one end or the other of the nanowire. Analysing the variation in the resistance induced by a heat-driven spin torque, represented by peaks occurring in correspondence with the GMR transition, we found that a temperature difference of the order of 5 K is sufficient to produce sizeable torque in spin valves.

EPFL2015

Short-Wavelength Spin Waves in Yttrium Iron Garnet Micro-Channels on Silicon

Jean-Philippe Ansermet, Ping Che, Sa Tu, Francesco Antonio Vetrò, Haiming Yu, Yan Zhang

Yttrium iron garnet (YIG) has been widely used in spin wave studies thanks to its low Gilbert damping constant. However, most high-quality YIG films are grown on gadolinium gallium garnet (GGG) substrate, which makes it difficult to integrate with existing semiconductor technology. We show spin wave excitation in a nanometer-thick YIG micro-channel on silicon substrate. The YIG is grown by pulsed laser deposition (PLD) in high-purity oxygen followed by rapid thermal annealing at 800 degrees C after deposition. Using meander coplanar waveguides at submicrometer scale, spin waves with wavelength down to 1 mu m are excited. By measuring the linewidth of the spin wave reflection spectra, a Gilbert damping constant alpha = 1.9 x 10(-3) was obtained.

Ieee-Inst Electrical Electronics Engineers Inc2016

Active Ferromagnetic Metasurface with Topologically Protected Spin Texture for Spectral Filters

Jilei Chen, Dirk Grundler, Haiming Yu

Electromagnetic metasurfaces modulate a material's response to electromagnetic waves by specifically arranged elements with dimensions below the wavelength. They have opened new fields of research, including flat optics and nanophotonics on a chip. Ferromagnetic metasurfaces could become the building blocks for manipulation of both microwaves and spin waves (magnons). So far, the functionality of magnonic devices has been limited by high intrinsic damping of the materials employed, suppressing long‐distance spin‐wave propagation. Here ferromagnetic metasurfaces are reported, which are created from periodic arrays of either 15 nm thick Co20Fe60B20, Ni80Fe20 or Co nanodisks on ferrimagnetic yttrium iron garnet (YIG) hosting topologically protected vortex states. This device, a reconfigurable spectral filter, operates in the microwave regime near 0.9 GHz and manipulates long‐distance spin wave transmission in thin YIG. An efficiency of 98.5% is demonstrated, with the metasurface covering only 15% of the microwave antenna. This first dem-onstration of a ferromagnetic metasurface opens unprecedented possibilities for on-chip control of microwaves in low-damping ferrimagnetic insulators.

2022

Effect of Heat Current on Magnetization Dynamics in Magnetic Insulators and Nanostructures

Francesco Antonio Vetrò

EPFL2015