Systematic study of surface magnetism in Si(111)–Fe system grown by solid phase epitaxy: In situ schematic magnetic phase diagram of Si(111)–Fe

Abstract We have studied in situ structures and magnetic properties for several iron silicides grown on Si(111)7×7 clean surfaces by the solid phase epitaxy (SPE) method: deposition of Fe at 40 K and subsequently annealing, and summarized almost all silicide phases depending on the deposition thickness and the annealing temperature as a “schematic magnetic phase diagram”. In the SPE growth, bcc-Fe(111)1×1, c-FeSi(111)1×1, 2×2, and c(4×8), α-FeSi2(112)2×2, ϵ-FeSi(111)√3 × √ 3-R30°, β-FeSi2(101)/(110) and polycrystalline phases are formed on Si(111)7×7 surfaces depending on Fe coverage (0.15–10.0 nm) and annealing temperature (470–1070 K). The structures and magnetic properties of all the above Fe silicide phases have been characterized by using in situ reflection high-energy electron diffraction, scanning tunneling microscopy, and surface magneto-optical Kerr effect. Bulk-unstable c-FeSi phases showed ferromagnetic property at 40 K and this ferromagnetism remained even after air exposure. For the c-FeSi(111)/Si(111) system, the large spin polarization was proposed at the Fe interface atoms in the B5-type interface structure between the c-FeSi(111) ultra-thin film and the Si(111) substrate by first-principle calculations.