Télécharger le sujet de stage - Laboratoire de Physique des Solides

MASTER DE PHYSIQUE ET APPLICATIONS - 2ème année
Spécialité Sciences des Matériaux et Nano-objets
UPMC Paris 6, ENS Ulm, Chimie ParisTech, ESPCI et l’École Polytechnique
Proposition de stage 2016-2017
Laboratoire: Laboratoire de Physique des Solides (LPS)
Adresse: bât 510, campus d’Orsay
Directeur du laboratoire: Sylvain RAVY
Responsable(s) du stage: João SAMPAIO & Alexandra MOUGIN
Téléphone: 0169156063
e-mail: [email protected]
Spin Transfer Torques In Ferrimagnetic Alloys
The aim of this project is to study the physics of spin transfer torque in ferrimagnetic thin films
and nanostructures. This subject is at core of magnetism and spintronics, and may lead to the
development of low consumption magnetic storage devices with attractive dynamic capabilities.
Spin transfer torque occurs when a spin polarised current is injected in a magnetic material,
relaxes its spin and exerts a torque on the local magnetisation. It has been shown that spin currents
can be used to propagate domain walls, to excite dynamic modes, or to reverse nanopillars,
although often requiring very large current densities. Recently, new ways of generating pure spin
currents have been discovered that are potentially more efficient, such as the Spin Hall effect or
through the use of topological insulators. These discoveries put forward again the study of the
underlying physics of spin transfer torques, as well as of the influence of parameters (choice of
materials, geometry...) on the efficiency of the effect.
Ferrimagnetic materials are Transition Metal / Rare Earth (TM/RE) alloys or multilayers in which
the TM (Co, Fe...) and RE (Tb, Gd...) magnetic sublattices are antiferromagnetically coupled.
Such ferrimagnets display unique magnetic properties. They exhibit a compensation temperature
(TComp) at which the net magnetisation vanishes due to the compensation of RE and TM
sublattices. TComp impacts on most magnetic quantities (magnetisation, anisotropy) that determine
the magnetisation reversal dynamics (damping, domain wall mobility...). Ongoing study of
domain wall dynamics under current (see figure) shows that the net magnetisation is a tuning
factor of the spin transfer torque. Our goal is now to use magnetotransport techniques to quantify
the spin transfer torque as function of the net magnetisation. Moreover, the determination of the
field-like or damping-like nature of the torques will clarify the microscopic mechanisms coupling
moving charges, spins and local magnetisation subblatices in ferrimagnetic alloys thin
nanostructures.
Superimposed magneto-optical Kerr images
showing the propagation of two DWs in a TbFe
10µm wide track under current and field. The
two DWs propagate at different velocities
because the current (J) pushes both DWs to the
left while the field (H) pushes both to centre.
Techniques utilisées : nanofabrication (physical vapour deposition, e-beam lithography),
high precision transport measurements, and magneto-optical Kerr imaging.
Qualités du candidat requises : Keenness for experimental work and critical analysis of data.
Rémunération éventuelle du stage : oui (environ €550)
Possibilité de poursuivre en thèse ? Oui
Si oui, mode de financement envisagé : Bourse école doctorale