Abstract:
A new class of electronic devices based on the quantum spin of the electron rather than on its charge has emerged in the last twenty years. These so-called "magneto-electronic" or "spintronic" devices have found straightforward application in data storage and sensing. More recently, a new physical effect has been discovered and attracted attention of the industry: when spintronic devices approach nanoscale size, high frequency dynamics can be excited by the mere application of a current. This effect, called "spin transfer torque" can extend the potential for applications of these devices to other fields, such as radiofrequency telecommunications and solid-state non-volatile data storage.
We report on our study on vortex-based spin transfer torque oscillators in nano-contact geometry. In particular, we show how the performance of these devices can be improved by exciting coupled dynamics of multiple vortices. Two different systems will be considered. In the first one, the vortices are all nucleated in the same ferromagnetic layer of a giant magnetoresistive (GMR) stack, with the other layer acting as a polarizer. In this case, which we will call horizontal coupling, interaction is mediated by anti-vortices and can lead to phase locking of the orbital motion of the vortices. In the second system, two vortices are stabilized under the same nano-contact, one in each of the two ferromagnetic layers of the GMR stack. In this case, which we will call vertical coupling, interaction is due to mutual spin-transfer torque with each layer acting as a dynamic polarizer for the other. Multiple modes can be excited, which can be selected by tuning the injected d.c. current.
We also introduce a complete new concept device for non-volatile data storage, in which ferromagnetism and resistive switching coexist in doped semiconductor oxides.
Coffee and tea will be served 20 minutes prior to the seminar.