Injection locking of spin torque nano oscillators using surface acoustic waves

Abstract

Conventional methods use RF currents or magnetic fields for injection locking the Spin Torque Nano Oscillators (STNO) devices. In this paper, we demonstrate the injection locking of STNO devices using the Surface Acoustic Waves (SAW). The SAW interacts with the free layer of the STNO devices through magneto elastic coupling. This interaction produces some effective magnetic field, which we show, can be used for injection locking of the STNO device. We have studied the dynamics of the injection locking process and how it depends upon the characteristics of the driving SAW signal in great details. This is done through macrospin as well as micromagnetic simulations. Our results suggest that SAW can be very good candidates for injection locking of the STNO devices with a locking range of 50 MHz and locking time of 10 ns for a strain of 100 ppm. This roughly corresponds to the requirement of RF current of amplitude 0.05 mA or field of amplitude 5 Oe, if we use the conventional methods. To explain our simulation results, we use the universal auto oscillator model. The amplitude of the locking signal depends strongly upon the power of the oscillations in case of SAW. We have extended the universal auto oscillator model to consider this effect and explain our results.