Dynamical and synchronization properties of vortex based spin-torque nano-oscillators

The research conducted during this PhD thesis aims at studying the microwave emission and the synchronization properties of nanoscale oscillators driven by the spin-transfer torque (STT) phenomenon. Moreover, the spin-transfer nano-oscillators (STNOs) considered in this work take advantage of the so-called non-uniform magnetic vortex states for creating new microwave emission technologies. The experimental device employed for the investigation of the vortex based STNOs, also called spin-transfer vortex oscillator (STVO), is a network of multilayered ferromagnetic nanowires produced electrochemically inside nanoporous anodic alumina oxide (AAO) templates. In addition to the device fabrication and characterization steps, a theoretical study of the magnetization dynamics in the constituent magnetic layers is conducted in the framework of nanomagnetism (micromagnetic simulations and analytical modelization). In our approach, each nanowire is composed of one or several Co/Cu/Co trilayers corresponding to the so-called spin valve (SV) structures that appear as a set of potential STNOs connected in series and/or parallel. Each SV is separated from the others by a relatively thick non-magnetic layer (50 to 100 nm). An interesting perspective of the nanowire devices is that such in series connected STNOs are expected to lead to synchronization phenomena. Synchronization between STNOs is at the center of the current concern since it represents a promising way for increasing the emitted power of such nano devices and for reaching the power required for practical applications. (FSA - Sciences de l) -- UCL, 2015