Nature Nanotech. http://doi.org/bbmz (2015)

Credit: NPG

A spin-polarized current injected in a ferromagnet is able to modify the magnetization direction due to spin transfer. This effect is used in spin-torque nano-ocillators to make the magnetization of a ferromagnet precess, enabling microwave generation. Taking advantage of their nonlinear behaviour and the propagating spin-waves generated by the spin precession, multiple nano-oscillators can be synchronized, allowing the total emitted microwave power to be increased. Now, Afshin Houshang and colleagues demonstrate that the Oersted field originating from the current passing through the nano-oscillator not only alters the emission pattern of the spin-waves but can be used to enhance the synchronization of several devices if simple array geometries are used. This represents an important step towards the development of practical applications. In particular, they demonstrate the synchronization of five nano-oscillators — a record-high number — and robust synchronization of two devices separated by distances longer than one micrometre.