We demonstrate how the combination of oscillating magnetic forces and
radio-frequency (RF) pulses endows RF photons with tunable momentum. We observe
velocity-selective spinflip transitions and the associated Doppler shift. This
realizes the key component of purely magnetic spin-orbit coupling schemes for
ultracold atoms, which does not involve optical transitions and therefore
avoids the problem of heating due to spontaneous emission.Comment: Corrections made to reference numbers in the main tex
