Study of the spin polarization of field‐emitted electrons from magnetic materials

We have constructed an apparatus for detecting the spin polarization P of field‐emitted electrons from magnetic material. It makes use of (i) a bakable superconducting coil allowing static operation of the external magnetic field H at the tip position and (ii) controlled field evaporation below 2×10−10 Torr (2.67×10−8 Pa) (using a channeltron for counting the field‐evaporated ions) without any imaging gas for cleaning the tip surface. We show that these ions) without any imaging gas for cleaning the tip surface. We show that these new features (not present in earlier investigations) coupled with a probe–hole arrangement are fundamental for a meaningful detection of P in field emission, especially for the measurement of P (H) and of the dependence of P on the crystallographic directions. Results for W(110), with P=0 within experimental accuracy and for various [hkl] directions of Ni, where small spin polarizations (i.e., <5%) have been detected are presented.