Presentation description

Spin torque oscillators are at the forefront of study in condensed matter physics, particularly spintronics. These magnetic oscillatory devices have many fascinating applications, specifically as compact tunable microwave sources and in nueromorphic computing. These applications often require frequency and power synchronization among many devices. However, recent experimental measurements have shown irregular mode splitting in the power spectral density (PSD) over several devices, which indicates that multi-device synchronization would be difficult. Computational simulations have recently shown that this device to device variation is likely due to random granular structure created during the fabrication process. The grains can have weakened exchange coupling at their barriers, which means that they struggle to magnetically "talk" to each other. This phenomenon is measured and simulated by decreasing a value called the inter-grain factor (IGF). This reduced IGF creates spin-wave reflections at grain boundaries that can lead to the experimental mode splitting in the PSD. In this study, we computationally investigate when these grains have differing magnetic properties in addition to the reduced IGF. In particular, we model the effect of atomic scale variations in thickness of each grain created during the fabrication process. This variation in thickness causes changes in the perpendicular magnetic anisotropy (PMA) of each grain. Our preliminary investigations have revealed that significant decrease or increase in the PMA of a single large enough grain can act as a spatial potential barrier in the system; this grain can divide the oscillatory region into two different regions that can oscillate independently, as the "dead" grain will reflect any spin-waves that attempt to cross the potential barrier. Because these two regions are decoupled magnetically other than long range dipole-dipole interactions, they are free to oscillate at different frequencies, thus producing the experimental mode splitting.