Magnetic characterization of synthetic ferrimagnets and spin-orbit torque efficiency evaluation.

This project was developed in a conjoint program between Institute Jean Lamour located in Nancy (France) and the New York University, in each institution, a significant part of the work was carried out with the important collaboration of the local teams. The topic of this work can be framed into what is called spintronics which is a fairly recent field of solid-state physics, in these years plenty of applications were invented among which the most important has to be found in magnetic memories, which is the specific application addressed by this project. In particular, we are referring to the newest approach found in the use of spin-orbit torque to achieve the latest generation MRAM which can be fabricated using CMOS compatible processes: SOT-MRAMs. This kind of memory, with respect to STT-MRAMs, carries mostly advantages, that are mainly related to the in-plane geometry for writing operations that removes the need for a high current passing through the magnetic layers. The central phenomenon of the study is therefore the spin-orbit torque (SOT), which can be generated by several microscopic phenomena, but the main two phenomena generally considered are the spin Hall effect and the Rashba-Edelstein effect. Both phenomena can be addressed as charge-to-spin conversion mechanisms meaning that an electrical current is transformed into a net spin current that if injected into a magnetic system exert a torque on the magnetization of the sample. This torque experimentally is never measured directly, what is done instead is modeling two effective fields (damping-like and field-like) that act on the dynamics of the magnetization following the so-called Landau-Lifshitz-Gilbert-Slonczewski equation. To study those phenomena, the project involved a first activity of cleanroom fabrication of the devices that will be used to perform some of the more advanced characterization techniques, in particular Hall measurements. Besides fabrication, the project is mainly intended as a study and characterization of the magnetic properties of samples containing synthetic ferrimagnets, to this aim, different techniques are used, and experimental protocols are established. The characterization in which we are interested regards finding the compensation temperature, calculating the spin-orbit torque efficiency, and eventually trying magnetization switching experiments.