High-frequency Vortex-based Spin Transfer Nano-oscillators

Description

The exploitation of the quantum spin of the electrons, together with their charge, has led to a new class of electronic devices. These so-called “magneto-electronic" or “spintronic” devices have found application in data storage and sensing. Their field of application can be extended to radiofrequency telecommunications. In nanometer-scale spintronic devices the application of an electrical direct current generates an alternating voltage in the radiofrequency range, because of the physical effect known as spin transfer torque.Spin-transfer radiofrequency oscillators have been, so far, proposed and studied in two device geometries: nano-pillars and nano-contacts. In both systems, either a uniform magnetic configuration or a magnetic vortex is excited through the transfer of spin angular momentum. Uniformly magnetized spin-transfer nano-oscillators can reach frequencies as high as 50 GHz or above but deliver too small output power to be of use in practical applications. A magnetic vortex that is made to gyrate into a patterned nano-magnet generates an output signal with larger power and still in the range of the GHz. A substantial increase of the power, in absence of an externally applied magnetic field, is obtained by making the vortex gyrate around a nano-contact to a magnetoresistive multilayer. Unfortunately, in vortex-based oscillators in nano-contact geometry the frequency is limited to a few hundreds of MHz.We here propose to study a novel device geometry, which can combine the power performance of the vortex-based nano-contact oscillators with the high-frequency performance of the vortex-based nano-pillar oscillators. The system consists of a hybrid geometry in which a magnetic vortex is made to gyrate into a patterned nano-magnet, like in the case of a nano-pillar, but outside the electrically-active area, like in the case of a nano-contact. The power delivered by these oscillators would be comparable to that delivered by a vortex-based nano-contact oscillator, but the output frequency is enhanced because of the lateral confinement of vortex due to the patterned geometry. These devices will be fabricated, characterized and analytically modeled. This will allow us, on one side, to contribute to the basic knowledge of the spin transfer torque and, on the other side, to demonstrate practical application of this new effect in radiofrequency telecommunications.