High-Power Coherent Microwave Emission from Magnetic Tunnel Junction Nano-oscillators with Perpendicular Anisotropy

TLDR

The excitation of steady‑state magnetization precessions by spin‑transfer torque offers a new route to nanoscale microwave oscillators, yet practical devices require higher output power and narrower linewidth. We demonstrate CoFeB‑MgO magnetic tunnel junctions with perpendicular anisotropy that generate 0.28 µW of microwave power and a 25 MHz linewidth, outperforming previous STNOs and enabling nanoscale alternatives to silicon oscillators.

Abstract

The excitation of the steady-state precessions of magnetization opens a new way for nanoscale microwave oscillators by exploiting the transfer of spin angular momentum from a spin-polarized current to a ferromagnet, referred to as spin-transfer nano-oscillators (STNOs). For STNOs to be practical, however, their relatively low output power and their relatively large line width must be improved. Here we demonstrate that microwave signals with maximum measured power of 0.28 μW and simultaneously narrow line width of 25 MHz can be generated from CoFeB-MgO-based magnetic tunnel junctions having an in-plane magnetized reference layer and a free layer with strong perpendicular anisotropy. Moreover, the generation efficiency is substantially higher than previously reported STNOs. The results will be of importance for the design of nanoscale alternatives to traditional silicon oscillators used in radio frequency integrated circuits.