An all-electrical spin resonance effect in a GaAs few-electron double quantum dot is investigated
experimentally and theoretically. The magnetic field dependence and absence of associated Rabi
oscillations are consistent with a novel hyperfine mechanism. The resonant frequency is sensitive to
the instantaneous hyperfine effective field, and the effect can be used to detect and create sizable nuclear polarizations. A device incorporating a micromagnet exhibits a magnetic field difference between dots, allowing electrons in either dot to be addressed selectively.