Nanowire spin Hall oscillators: width dependence

We present experimental studies of auto-oscillatory magnetization dynamics in nanowire spin Hall oscillators (SHOs) as a function of the wire width ranging from 0.17 µm to 2 µm. These SHOs consist of long Pt(7 nm)/Py(5 nm)/AlOx(2 nm) wires on a sapphire substrate. Direct current generating anti-damping spin torque is applied to a section of the wire between two leads separated by a 2 µm gap, which defines the SHO active region.$^{1}$ All devices show onset of auto-oscillations at similar critical current densities. For the 0.17 µm and 0.34 µm wide nanowire SHOs, auto-oscillatory modes arising from the bulk and edge eigenmodes of the nanowire are clearly seen in the emission spectra. For SHO devices based on wider wires, the bulk auto-oscillatory modes dominate the emission spectrum due to the larger wire volume occupied by the bulk modes. Our work demonstrates robust operation of nanowire-based SHOs over a wide range of nanowire widths and presents an example of a spin torque oscillator with the active area extended into the µm$^{2}$ domain. [1] Zheng Duan et al, Nature Communications 5, 5616 (2014)