Nano-scale oscillations in new applications
Spin torque oscillators (STOs) are novel nano-scale oscillating devices based on spintronics technology and periodic flipping of magnetisation. Their tiny scale and high tunability make them very attractive for many applications, including the non-conventional. However, mechanisms are still poorly understood and understanding is a prerequisite for exploitation. EU-funded scientists initiated the project 'Spin torque oscillators with applications in non digital computing science and communications' (SPINTORQOSC) to enhance knowledge and facilitate implementation of biologically inspired computations in nanostructures. The focus was on spin wave excitations in ferromagnetic thin films, a phenomenon supporting new types of information processing. The team set out to implement wave front computations using spin waves analogous to computations by the brain exploiting periodic electrical oscillatory activity. Spin waves or magnons are elementary collective excitations of spins, where spin is the angular momentum inherent to all elementary particles. In STOs, very large magnitude magnetisation oscillations are maintained. Theoretical work led to achievement of the first goal and publications of a model for implementing biologically inspired computations with wave fronts in nanostructures. Scientists proposed a concept consisting of ferromagnetic thin films where the spin waves propagate and nanocontacts (the STOs) that contact the films and excite magnetisation dynamics. Thus, the STOs both create spin wave patterns and, at the same time, sense incoming spin waves. Experimental work led to fabrication of STO devices on ferromagnetic thin films and demonstration of spin wave activity in them measured electrically. The team has also investigated various methods for imaging and controlling the spin waves, including the use of two different synchrotrons and the use of organic semiconductors. Coupling between magnetic thin films and the organic semiconductors led to discovery of a new effect, transduction of a magnetic signal into an optical one via electroluminescence in the organic semiconductor. Other work focused on single-molecule magnets and fabrication of a number of STO devices. SPINTORQOSC outcomes have been published in numerous papers in prestigious peer-reviewed scientific journals. Through theory and experiment, scientists have deepened understanding of STOs and their mechanisms and control. Exploitation in novel devices is around the corner.
Keywords
Magnetisation, spin torque oscillators, computing science, spin wave, ferromagnetic thin films
