  Spin-polarized scanning tunneling microscopy (SP-STM) experiments on
ultrathin films with non-collinear spin textures demonstrate that resonant
tunneling allows for atomic-scale spin-sensitive imaging in real space at
tip-sample distances of up to 8 nm. Spin-polarized resonance states evolving
between the foremost atom of a magnetic probe tip and the opposed magnetic
surface atom are found to provide a loophole from the hitherto existing dilemma
of losing spatial resolution when increasing the tip-sample distance in a
scanning probe setup. Bias-dependent series of SP-STM images recorded via
resonant tunneling reveal spin sensitivity at resonance conditions, indicating
that the spin-polarized resonance states act as mediators for the spin contrast
across the nm-spaced vacuum gap. With technically feasible distances in the nm
regime, resonant tunneling in SP-STM qualifies for a spin-sensitive read-write
technique with ultimate lateral resolution in future spintronic applications.
