In the device investigated by Liu et al. , a magnetic field H defines the stable equilibrium position of the magnetization M in the ferromagnetic Permalloy layer. The gold contacts enable a high charge-current density I in a small area of the platinum/Permalloy bilayer. The part of the current that flows through the platinum generates a spin current in the platinum (Pt) layer between the gold (Au) and Permalloy (Py) interfaces, with a net spin accumulation developing at the platinum/Permalloy interface. This spin accumulation reduces the magnetic damping in the adjacent ferromagnetic Permalloy layer, which in turn gives rise to spontaneous excitation of magnetization precession (wider cones). The resistivity changes associated with the time varying magnetization subsequently result in voltage changes and concomitant microwave generation at the rf frequencies characteristic for the magnetization precession.