Spin torque oscillator (STO) is a tiny magnetic layer stack which
oscillates in microwave frequency range simply by injecting a DC
current. However, the performance of a single STO, such as power level
and frequency stability, is not good enough for practical application.
Some past works observed mutual phase locking between two STOs formed
close to each other. It was found that a mutually phase locked STO pair
shows significantly better performance than a single STO. Therefore, it
is a natural extension to try to synchronize multiple STOs for even
better performance, but to the authorís knowledge, no research group has
published any success of such an attempt as of 2008.
It is believed that interaction between spin waves and a STO is the
underlying mutual phase locking mechanism. One STO launches spin waves
as it oscillates, and the oscillation of the other STO is synchronized
to the incident spin wave. However, spin wave propagation is much more
complicated than usual 2D wave propagation such as membrane vibration,
and so far no quantitative study has been conducted either
experimentally or theoretically.
We have a Kerr imaging system for capturing spin wave propagation. The
goal of this project is to study the interaction between the incident
spin wave and STO by using this system in order to understand the mutual
phase locking mechanism quantitatively, and eventually gain new insight
for designing and characterizing multiple STO synchronization devices.