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Spin-polarized vacuum tunneling has been achieved in field emission from spontaneously and remanently magnetized ultrathin film Co-coated W(111) tips. The onset thickness of polarization at room temperature, equivalent to 3 Co (0001) layers, and the transverse spin-polarization directions are consistent with magnetic properties of Co films on macroscopic W(111) single-crystal surfaces. The orientation of the polarization vector in any of 12 transverse directions is due to crystallographic symmetry and the influence of tip morphology. Polarization of 10%–25% was obtained typically, while the highest recorded value was 48%. Manipulation of the polarization direction and magnitude were also achieved by application of transverse magnetic field pulses and demagnetization. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Superparamagnetic fluctuations of magnetization in thin Fe films that coat a sharp W(001) tip are evident in the spin polarization of field emitted electrons. Fluctuations of polarization between four transverse directions that align with the tip <100> directions are consistent with the in-plane biaxial magnetization of Fe films on macroscopic W(001) surfaces. This superparamagnetic behavior imposes a limit to spin polarized vacuum tunneling applications that proves to be more stringent than the suppression of the Curie temperature in thin films due to finite size effects. [ABSTRACT FROM AUTHOR]