Frequency dependence study of a bias field-free nano-scale oscillator

Oscillators belong to the group of fundamental building blocks and are ubiquitous in modern electronics. Especially spin torque nano oscillators are very attractive as cost effective on-chip integrated microwave oscillators, due to their nano-scale size, frequency tunability, broad temperature operation range, and CMOS technology compatibility. Recently, we proposed a micromagnetic structure capable of operating as non-volatile flip flop as well as a spin torque nano oscillator. The structure consists of three anti-ferromagnetically coupled stacks (two for excitation A, B and one for readout Q) and a shared free magnetic layer. Micromagnetic simulations show a current regime, where the structure exhibits large, stable, and tunable in-plane oscillations in the GHz range without the need of an external magnetic field or an oscillating current. In this work the dependence of these oscillations on the shared free layer geometry at a fixed input current is studied. It is shown that the precessional frequency can be controlled by the dimensions of the shared free layer. Most efficient is to utilize the layer thickness to control the precessional frequency, but also changing the layer length can be exploited.