Characterization of Fe/W spin-polarized tips by means of holographic TEM and spin-polarized STS of optically pumped p-GaAs

Holographic transmission electron microscopy showed that magnetic flux does not diverge from the top of an Fe-coated W tip indicating the in-plane magnetization at the apex of successful spin-polarized tips. A dependence of differential conductivities of GaAs with Fe-coated W tips on the helicity of illuminating laser light was confirmed at negative sample bias where partially spin-polarized electrons in the conduction band of p-GaAs tunnel into spin-dependent Fe empty states while no dependence of those with nonmagnetic W tips. Index Terms--Magnetic field measurement, optical pumping, spectroscopy, tunneling.