Domain wall propagation induced by spin polarized current

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Ajouté le: 14/11/2014
Directeur : VERNIER Nicolas -
Titre : Domain wall propagation induced by spin polarized current
Thèmes : Électronique, opto-électronique, Nano-sciences, nanotechnologies
Laboratoires : IEF - Institut d'Electronique Fondamentale UMR 8622
Description :

In a ferromagnetic thin film, there are magnetic domains, which are parts inside which the magnetization is uniform. Between two domains, there is an intermediate part called domain wall, in which magnetization goes continuously from the direction of the first domain to the one of the second domain. To reverse magnetization in a magnetic thin film, one possibility is to nucleate one reversed domain, then the domain grows due to propagation of the domain wall at its boundaries. Until recently, this propagation was induced by a magnetic field, according to the torque generated this way.

For now somme ten years, it has been shown that domain walls could be moved through a new way : by sending a spin polarized current through the domain wall. The current gets spin polarized when going through the domain. Then, it generates a torque on the local magnetic moments when it arrives at the domain wall. This torque pushes the domain wall forward. In some cases, it becomes even possible to move a domain wall in zero magnetic field. This new process behaves in ways completely different from what we have been used to with magnetic field and it is far from being understood.

For example, in GaMnAs nanowires (diluted ferromagnetic semiconductor), we have found that the velocity propagation depended on the width of the domain wall (see figure). The aim of the student will be going on in the experiments and analyze the results to get a better understanding of this new way to move domain walls. This project has got support from several contracts.

The work has two sides : experiments and therory. For the experimental part, the student will use the facilities of the 'Centrale de Technologie Universitaire' to make and pattern his sample. Some of the work will be done with the help of other laboratories (LPN for the GaMnAs samples, LPS for the analysis of the results). Propagation and domain wall shape will be studied using Kerr microscopy. Analysis will be done using analytical models, but also, for complexe configuration, numerical simulations.

 Kerr imaging of spin polarized current induced propagation in GaMnAs nanowires : between each picture, a current pulse was sent in the wire.