Ferromagnetic iron silicides on Si(111) surface grown by solid phase epitaxy
Hattori, Azusa; Hattori, Ken; Katayama, Yasuto; Kodama, Kenji; Hosoito, Nobuyoshi; Komori, Fumio; Hiroshi, Daimon
Japan

Iron silicides have attracted much attention from device engineers. β-FeSi2, for example has been investigated and applied to infrared light emitting devices. If certain Fe-Si systems grown on Si surfaces have ferromagnetic properties (expected to be different properties from the bulk phases due to their quasi two-dimensional character), they might be applied to magnetic semiconductors as new materials. In order to survey ferromagnetic Fe-Si systems, we have investigated their structure and magnetic properties of Si(111)-Fe surfaces experimentally by RHEED and SMOKE in-situ in a ultra-high vacuum and SQUID, VSM, XRD, cross-section TEM ex-situ. We have prepared various Fe silicides by the solid phase epitaxy [1]. Fe was deposited at different thicknesses on Si(111)-7X7 clean surfaces at 40 K and subsequently annealed. After cooling the sample to 40 K both RHEED and SMOKE measurements were carried out. After in-situ experiments, any ex-situ measurements have been done for each phase. We found that the ferromagnetic properties appear in some phases: bcc-Fe(111), 2X2-Fe, polycrystals and β-FeSi2. The 2X2 phase has been suggested to be c-FeSi with CsCl-based structure [2], which is metastable in bulk. We suggest that the interface ferromagnetism in 2X2-Fe phase due to its B5 type interface.
For polycrystal phase also has a ferromagnetic property. RHEED, XRD and TEM revealed that this phase is composed of β-FeSi2and Fe3Si. Ferromagnetism must be attributable to Fe3Si component.
The bulk β-FeSi2 is not ferromagnetic, however, our sample with β-FeSi2at surface showed hysteresis loops indicating ferromagnetism appeared. Cross-section TEM analysis revealed that a ferromagnetic Fe3Si phase is formed at the interface between the Si substrate and the β-FeSi2 film. In this presentation, we will discuss the details of the structure and magnetic properties of several iron silicide phases on Si(111) surfaces.
References: [1] K. Kataoka et al., Phys. Rev. B 74, 155406 (2006).
[2] S. Walter et al., J. Phys.: Condens. Matter 15, 5207 (2003).
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