Maximum magnitude in bias-dependent spin accumulation signals of CoFe/MgO/Si on insulator devices

We study in detail how the bias voltage (V_bias) and interface resistance (RA) depend on the magnitude of spin accumulation signals (ΔV or ΔV/I, where I is current) as detected by three-terminal Hanle measurements in CoFe/MgO/Si on insulator (SOI) devices with various MgO layer thicknesses and SOI carrier densities. We find the apparent maximum magnitude of spin polarization as a function of V_bias and the correlation between the magnitude of spin accumulation signals and the shape of differential conductance (dI/dV) curves within the framework of the standard spin diffusion model. All of the experimental results can be explained by taking into account the density of states (DOS) in CoFe under the influence of the applied V _bias and the quality of MgO tunnel barrier. These results indicate that it is important to consider the DOS of the ferromagnetic materials under the influence of an applied V_bias and the quality of tunnel barrier when observing large spin accumulation signals in Si.