PhD defense : Spin orbit torques measurements in Pt-based heavy metal / Ferromagnet heterostructures with in-plane magnetic anisotropy

On Friday, the 16th Of June 2017 at 14h00, Alexandru TRIFU from CEA (DRF/INAC/SPINTEC), will defend his PhD thesis entitled “Spin orbit torques measurements in Pt-based heavy metal / Ferromagnet heterostructures with in-plane magnetic anisotropy”
Place : Amphithéâtre du CNRS bâtiment A-3ème étage – 25 rue des Martyrs, Grenoble

Recent demonstrations of magnetization switching induced by in-plane current injection in heavy metal (HM)/ferromagnet (FM) heterostructures have drawn increasing attention to spin-torques based on orbital-to-spin momentum transfer induced by Spin Hall and interfacial effects (SOTs). Unlike STT-MRAM, the in-plane current injection geometry of SOT-MRAM allows for a three-terminal device which decouples the “read” and “write” mechanisms, allowing the independent tuning of reading and writing parameters. However, an essential first step in order to control and optimize the SOTs for any kind of application, is to better understand their origin. The origin of the SOTs remains one of the most important unanswered questions to date. While some experimental studies suggest a SHE (Spin Hall Effect)-only model for the SOTs, others point towards a combined contribution of the bulk (SHE) and interface (Rashba Effect and Interfacial SHE). At the same time, many studies start with a SHE only hypothesis and do not consider interfacial effects. Furthermore, there are not so many systematic studies on the effects of interfaces.

This thesis tries to fill in this gap, by providing a systematic study on the effects of interfaces on the SOTs, in Pt-based NM/FM/HM multilayers with in-plane magnetic anisotropy. For this purpose, three different, but related avenues, are explored. First, the evolution of the Damping-Like and Field-Like effective fields is studied as a function of Pt layer thickness. Next, the properties of the interfaces are changed by modifying the crystallographic structure of the interface. Last but not least, we studied the influence of interface oxidation on the anatomy of the torques.

Jury :
Sayeef SALAHUDDIN, University of California
Jan VOGEL, CNRS-Institut Néel
Juan Carlos ROJAS SANCHEZ, CNRS-University of Lorraine
Mihai GABOR, University of Cluj-Napoca

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