Microwave Generation in Magnetic Multilayers and Nanostructures

Abstract

AbstractWe present an overview of the coherent magnetic precessional dynamics induced by the spin‐transfer effect in magnetic nanostructures. The precessional frequencies of the magnetic oscillators can be tuned over a range of several gigahertz by varying the dc current through the devices. The oscillation frequencies also depend on the applied magnetic field, resulting in a nanoscale oscillator that can be tuned from a few gigahertz to greater than 40 GHz. Even at room temperature, the linewidths of these excitations are often only a few megahertz wide. This gives quality factors for the excitations of more than 18 000 at the highest frequencies. As the direction of the applied field changes from parallel to perpendicular to the film plane, the power output from the structures increases by several orders of magnitude. For fields applied nearly perpendicular to the film plane, the high‐frequency voltage output from the device can be a significant fraction of the maximum voltage expected from the giant magnetoresistance effect. The nanoscale oscillators also display a number of attributes making them attractive for potential technological applications. These include the ability to frequency modulate the devices, phase lock them to external reference signals, and electronically control their phase relative to that of an input signal.