Magnetic anisotropy versus morphology in Fe films deposited on ultrathin iron silicides

Abstract

The correlation between growth and magnetic anisotropy of thin Fe films deposited on ultra thin iron silicide template grown on Si(111) is investigated by means of scanning tunnelling microscopy and magneto optical Kerr effect experiments. The morphology of the film strongly depends on the Fe beam orientation relative to the sample normal. Whereas the Fe clusters are randomly distributed at normal incidence, oblique evaporation leads to the formation of elongated Fe islands perpendicular to the Fe beam. These distinct growth modes lead to drastically different magnetic anisotropies. An in-plane six-fold anisotropy magnetic easy axis has been evidenced for films deposited at normal incidence. The films evaporated at oblique incidence show an uniaxial in-plane magnetic easy axis parallel to the Fe stripes. This uniaxial anisotropy originates from long-ranged dipolar interactions.It has been previously observed that an artificial in-plane uniaxial magnetic anisotropy can be induced in thin ferromagnetic films by different methods such as deposition on stepped substrate [1], grazingincidence deposition on flat substrate [2-5] or low-temperature grazing incidence ion sputtering after the deposition at normal incidence of the magnetic layer [6]. In the case of oblique incidence deposition of Fe films on MgO(001) substrate, two different interpretations have been proposed in the literature to explain this uniaxial in-plane magnetic anisotropy. On one hand, Durand [3] suggested that this anisotropy results from magneto-elastic effects due to an in-plane tetragonal distortion of the cubic Fe structure. On the other hand, Park [2] and Wolfe [5] proposed that this magnetic anisotropy originates from an anisotropic surface roughness. This last interpretation has been also suggested in the case of thin Co films deposited on Cu(001) [4].In this paper, we investigate the influence of the deposition geometry on the morphology and the magnetic anisotropy in thin Fe layers. We show that the uniaxial anisotropy for oblique-incidence deposition originates from long-ranged dipolar interactions.The film deposition, the structural and morphological characterizations were done in situ in an ultra high vacuum chamber equipped with Scanning Tunnelling Microscopy (STM), Low Energy Electron Diffraction (LEED) and X-rays Photoelectron Diffraction (XPD) facilities. The magnetic anisotropy has been measured ex situ with the recent Transversely Biased Initial Inverse Susceptibility and Torque (TBIIST) method described in details in the reference [7]. Prior to Fe deposition at room temperature, an ultra thin and atomically flat iron silicide layer with c(4x8) periodicity was grown on the Si(111) wafer [8]. This template layer prevents the diffusion of Si into the Fe layer and improves the epitaxy of the Fe

Molecular-beam epitaxy of Heusler alloy thin films epitaxially grown on Si(001)

“…This observation is qualitatively similar to that found in previous experimental studies [19][20][21][22][23], where the easy magnetization was found preferential along the direction perpendicular to the fluxes incidence plane. The origin of the observed in-plane uniaxial anisotropy is probably due essentially to longrange dipolar interaction as in the case of iron deposited on Si [18,24].…”

Polarized neutron reflectometry of the influence of Fe/Si, Fe/FeSi2 and Au/Fe interfaces on the magnetic properties of epitaxial Fe films

“…Fe layers (27 nm thick) were evaporated, at room temperature and at normal incidence with respect to the Si(111) substrate surface. This deposition geometry prevents the formation of an anisotropic roughness, which can lead to some specific magnetic anisotropy properties [16][17][18]. The atomic structure of the Fe films has been previously determined on the basis of LEED, X-ray photoelectron diffraction (XPD) and X-ray diffraction (XRD) measurements [19][20][21].…”

Magnetic shape anisotropy calculations of Fe nanostructures at the Si/Fe(111) interface

“…7:8 Â 10 14 atoms=cm 2 . The Fe deposition is performed at normal incidence with respect to the substrate surface so that the Fe surface three-fold rotational symmetry is conserved [9,24]. The resulting Fe films showed the expected bcc structure with the epitaxial orientation: Feð1 1 1Þ/1 2 1S // Sið1 1 1Þ/1 2 1S.…”