Epitaxial Fe-Ge thin films on Ge(111): Morphology, structure, and magnetic properties versus stoichiometry

Journal Article · Thu Apr 15 00:00:00 EDT 2010 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.81.155423· OSTI ID:21366730

Jaafar, R; Berling, D; Garreau, G ^[1]; Sebilleau, D ^[2]

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1. Institut de Science des Materiaux de Mulhouse, CNRS-LRC 7228, Universite de Haute-Alsace, Mulhouse (France)
2. Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes, UMR CNRS-UR1 6251, Universite de Rennes-1, 35042 Rennes Cedex (France)

We have studied the growth and magnetic properties of thin Fe-Ge films synthesized (codeposited at room temperature and postannealed at 250 deg. C) on Ge(111) wafers versus stoichiometry. Morphology and crystal structure have been investigated in situ by means of scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron diffraction and ex situ with x-ray diffraction. The magnetic properties were characterized ex situ by conventional polar and longitudinal magneto-optical Kerr effect and transverse biased initial inverse susceptibility and torque measurements. It is found that the growth is epitaxial for Ge content up to approx48 at. % (approxFe{sub 1.1}Ge composition). In particular, the film is homogeneous and flat and adopts a crystalline structure of hexagonal symmetry derived from the B8{sub 2} (Ni{sub 2}In) structure over a wide stoichiometry range extending from Fe{sub 2}Ge to Fe{sub 1.1}Ge. The epitaxial orientation between the Ge substrate and the germanide layer is (0001)Fe-Ge||(111)Ge with [1120]Fe-Ge||110]Ge. We found however that the surface periodicity and the out-of-plane lattice parameter c evolve within this stoichiometry range and two distinct stoichiometry regimes appear on both sides of a critical stoichiometry (approxFe{sub 1.5}Ge). Indeed, from Fe{sub 2}Ge to Fe{sub 1.5}Ge the surface periodicity is p(2x2) and c continuously decreases with Fe content, whereas from Fe{sub 1.5}Ge to Fe{sub 1.1}Ge the surface periodicity is (sq root(3)xsq root(3))R30 deg. and c remains constant. These features have been interpreted as a clear fingerprint of a minor transformation of the crystalline structure but without any change in symmetry. This structural order transformation is discussed in relation to previous results reported in the case of macroscopic single-crystal Fe-Ge ingots. On both sides of the wide [Fe{sub 2}Ge,Fe{sub 1.1}Ge] composition range the layer is no more homogeneous. More precisely, for higher Fe content the film contains both the above mentioned Ni{sub 2}In-derived phase and a Fe-richer phase (probably bcc Fe) whereas for higher Ge content the layer is amorphous. Magnetic characterization showed in particular that the homogeneous Ni{sub 2}In-derived epilayers are ferromagnetic with a Curie temperature that varies drastically with the stoichiometry, rising up to a high T{sub C} value of approx450 K for the Fe-rich Fe{sub 1.9}Ge composition. Finally, whatever the stoichiometry, the magnetic easy axis of the homogeneous phase lies in the film plane and a small uniaxial anisotropy is superimposed on a sixfold order one that results from the hexagonal symmetry of the crystallographic structure.

• OSTI ID: 21366730
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 81, Issue 15; Other Information: DOI: 10.1103/PhysRevB.81.155423; (c) 2010 The American Physical Society; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANISOTROPY
BCC LATTICES
CRYSTAL GROWTH
CRYSTAL STRUCTURE
CRYSTALLOGRAPHY
CURIE POINT
ELECTRON DIFFRACTION
EPITAXY
GERMANIUM
IRON
KERR EFFECT
LATTICE PARAMETERS
LAYERS
MAGNETIC PROPERTIES
MONOCRYSTALS
PERIODICITY
SCANNING TUNNELING MICROSCOPY
STOICHIOMETRY
SUBSTRATES
SURFACES
SYMMETRY
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
THIN FILMS
TORQUE
TRANSFORMATIONS
TRANSITION TEMPERATURE
X RADIATION
X-RAY DIFFRACTION
COHERENT SCATTERING
CRYSTAL GROWTH METHODS
CRYSTAL LATTICES
CRYSTALS
CUBIC LATTICES
DIELECTRIC PROPERTIES
DIFFRACTION
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
ELEMENTS
FILMS
IONIZING RADIATIONS
METALS
MICROSCOPY
PHYSICAL PROPERTIES
RADIATIONS
SCATTERING
TEMPERATURE RANGE
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENTS
VARIATIONS