  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 non-relativistic 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
non-equilibrium spin polarization of carriers. In our structure, this
linear-in-current magnetoresistance reaches 0.2\% at current density of $10^6$
A cm$^{-2}$.
