Spin polarization vectors of field emitted electrons from Fe/W tips

The atomic and electronic structures at the apex of W tips were studied by means of field ion microscopy and field emission microscopy, before and after the thermal deposition of a 5 nm Fe film. Two geometries of W tip, a conventional hemi-spherical type and a chisel ( flat needle) type, were prepared. The hemispherical and the chisel W tips had a h < 110 > direction parallel and perpendicular to the tip axis, respectively. The coated Fe films were found to be most likely in a non-crystalline phase, and to have a lower work function leading to a drastic change in electron emission from the apexes. The spin-polarization vectors of field-emitted electrons from these Fe/W tips were investigated with a Mott detector with a rotatable mechanism of tips. A similar absolute value of the spin-polarization vector vertical bar(P) over right arrow (tip)vertical bar = 0.415 +/- 0.025 was obtained for each Fe/ W, while the direction of the spin- polarization vector was dependent on the shape of the apex. The angle from the tip axis was theta = 45 degrees for the hemispherical apex and theta = 66 degrees for the chisel apex. A spin- polarized scanning tunneling microscopy setup with a rotation mechanism of such Fe/ W tips made it possible to detect both the in- plane and the out- of- plane spin component of a sample magnetization.