Spin-polarized scanning tunneling microscopy of the room-temperature antiferromagnetc-FeSi

Abstract

Antiferromagnetic spin ordering has been revealed by room-temperature spin-polarized scanning tunneling microscopy (SP-STM) in thin epitaxial films of $c$-FeSi on Si(111). Spin polarization of tunneling current for unoccupied states is found to be unusually large ${I}_{\ensuremath{\uparrow}\ensuremath{\uparrow}}/{I}_{\ensuremath{\downarrow}\ensuremath{\uparrow}}=3.8$. Atomically sharp spin-frustration domain walls, developing on the surfaces of nanoscale islands, have been observed on SP-STM images. Our results suggest that antiferromagnetism in $c$-FeSi is driven by Mott-Hubbard transition, and the atomically narrow domain walls are caused by local insulator-to-metal breakdown.