Quantitative detection of electrically injected spin accumulation in   GaAs using the magneto-optical Kerr effect
  Using an ultra sensitive magneto-optical Kerr rotation setup we have observed electrical spin injection from (Zn,Mn)Se into bulk GaAs and quantified the spin injection efficiency. The current induced contribution was carefully separated from possible artifacts and studied as a function of voltage and external magnetic field. Our measurements allow us to estimate the concentration of the electrically injected spins into GaAs to be approximately 0.4$\times10^{15}$cm$^{-3}$ at a reverse bias of 0.7 V. 
A.V. Kimel, A. Kirilyuk, P. Grabs, F. Lehmann, A. A. Tsvetkov, G.   Schmidt, L.W. Molenkamp, and Th. Rasing