Electrical detection of magnetization reversal without auxiliary magnets

First-generation magnetic random access memories based on anisotropic magnetoresistance required magnetic fields for both writing and reading. Modern all-electrical read/write memories use instead nonrelativistic spin transport connecting the storing magnetic layer with a reference ferromagnet. Recent studies have focused on electrical manipulation of magnetic moments by relativistic spin torques requiring no reference ferromagnet. Here we report the observation of a counterpart magnetoresistance effect in such a relativistic system which allows us to electrically detect the sign of the magnetization without an auxiliary magnetic field or ferromagnet. We observe the effect in a geometry in which the magnetization of a uniaxial (Ga,Mn) As epilayer is set either parallel or antiparallel to a current-induced nonequilibrium spin polarization of carriers. In our structure, this linear-in-current magnetoresistance reaches 0.2% at current density of 10(6) A cm(-2).