Observation of vacuum tunneling of spin-polarized electrons with the scanning tunneling microscope

Vacuum tunneling of spin-polarized electrons from a ferromagnetic ${\mathrm{CrO}}_2$ tip into a Cr(001) single crystal has been observed by means of a scanning tunneling microscope (STM) operated in UHV. Topographic STM images of the Cr(001) surface using a tungsten tip confirm the model of topological antiferromagnetism between ferromagnetic terraces separated by monatomic steps of 0.144 nm height. With ${\mathrm{CrO}}_2$ tips, the measured step-height values alternate around the mean value of 0.144 nm due to an additional contribution from spin-polarized-electron tunneling.