Electric field control of spin waves in ultrathin CoFeB films

Recently, investigation and control of the properties of propagating spin waves (SWs) in ultrathin ferromagnetic films have attracted considerable attention because of their possible technological impact on future nanoscale magnonic devices. Control of SW properties using voltage-controlled magnetic anisotropy (VCMA) may reduce the power consumption of future magnonic devices significantly. Here, we report an experimental study of manipulation of uniform ferromagnetic resonance (UFMR) and dipole-exchange SWs by VCMA in ultrathin Co20Fe60B20 (CoFeB) films with thicknesses of 1.6, 1.8, and 2.0 nm. The UFMR and the SWs are excited using microwave antennae and detected by spin pumping and inverse spin Hall effect techniques. A significant change in the SW frequency caused by VCMA is observed, particularly in the 1.6-nm-thick CoFeB film, where the effective value of the net anisotropy is quite small because of the presence of strong interfacial perpendicular magnetic anisotropy. Additionally, micromagnetic simulations are performed to demonstrate that the SWs in the 1.6-nm-thick CoFeB film with its in-plane easy axis of magnetization can be guided through virtual nanochannels formed by VCMA.