  We report a giant spin Hall effect (SHE) in {\beta}-Ta that generates spin
currents intense enough to induce efficient spin-transfer-torque switching of
ferromagnets, thereby providing a new approach for controlling magnetic devices
that can be superior to existing technologies. We quantify this SHE by three
independent methods and demonstrate spin-torque (ST) switching of both
out-of-plane and in-plane magnetized layers. We implement a three-terminal
device that utilizes current passing through a low impedance Ta-ferromagnet
bilayer to effect switching of a nanomagnet, with a higher-impedance magnetic
tunnel junction for read-out. The efficiency and reliability of this device,
together with its simplicity of fabrication, suggest that this three-terminal
SHE-ST design can eliminate the main obstacles currently impeding the
development of magnetic memory and non-volatile spin logic technologies.
