| 1. |
- Gallas, B., et al.
(författare)
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Changes in optical properties of MnAs thin films on GaAs(001) induced by a- to B-phase transition
- 2008
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Ingår i: Physica Status Solidi (a) applications and materials science. - : Wiley-VCH Verlagsgesellschaft. - 1862-6300 .- 1862-6319. ; 205:4, s. 859-862
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Tidskriftsartikel (refereegranskat)abstract
- MnAs layers with 45 nm thickness were grown epitaxially on GaAs(001) substrates. Ellipsometry measurements were made in the spectral range 0.045 eV to 6 eV as a function of temperature (between –10 °C and 50 °C) at 70° of incidence. In this way the transition from the hexagonal α-phase to the orthorhombic β-phase could be monitored. Non-zero off-diagonal elements of the Jones matrix for an azimuth of 38° off the [10] axis of the substrate indicate that the optical functions of MnAs are anisotropic in both phases. The optical conductivity exhibits low-energy interband transitions around 0.3 eV, more clearly seen in the α-phase than in the β-phase. Extrapolation of the optical conductivity to zero frequency confirms that the α-phase is about two times more conducting than the β-phase. A broad structure is observed in the visible range around 3 eV. The α-phase is characterised by an anisotropy induced energy difference of this structure with a maximum at 2.8 eV for the extraordinary index and at 3.15 eV for the ordinary index. This difference vanishes in the β-phase in which anisotropy mainly induces changes in amplitude of the 3 eV structure. The assignment of the structures will be discussed.
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| 2. |
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| 3. |
- Gustavsson, Fredrik, et al.
(författare)
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Magnetic moment and anisotropy at the Fe/ZnSe(001) interface studied by conversion electron Mössbauer spectroscopy
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:2, s. 024405-
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Tidskriftsartikel (refereegranskat)abstract
- The interface magnetic properties of Fe/ZnSe heterostructures grown on GaAs(001) by molecular-beam epitaxy have been investigated using conversion electron Mössbauer spectroscopy (CEMS) and macroscopic magnetic measurements. For Fe films thinner than 100 Å an in-plane 〈110〉 uniaxial magnetic anisotropy was found and the magnetization loops could successfully be described by the simple Stoner-Wohlfarth model, which implies that the magnetization reverses only by coherent rotation and jump processes. For the interface analysis, a 5-Å-thick layer of enriched 57Fe was deposited on the ZnSe surface and buried under 20 Å of natural Fe. In this way the 57Fe serves as a local probe of the interface magnetic environment in a bulklike Fe film since the CEMS technique is only sensitive to this isotope of Fe. An interface magnetic moment of 2.18 μB was found and, in relation to 2.2 μB for bulk bcc Fe, this precludes the presence of any interface reactions. Surprisingly, however, the direction of the interface magnetic moment turned out to be reoriented from the [110] direction by almost 30°, an effect that was assumed to arise from the distribution of unidirectional tetrahedral bonds present on the Zn c(2×2) reconstructed ZnSe surface.
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| 4. |
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| 5. |
- Gustavsson, Fredrik, et al.
(författare)
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Structural and transport properties of epitaxial Fe/ZnSe/FeCo magnetic tunnel junctions
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 64:18, s. 184422-
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Tidskriftsartikel (refereegranskat)abstract
- The use of a semiconductor barrier in heteroepitaxy with ferromagnetic metal electrodes describes a novel type of magnetic tunnel junctions. In this work, epitaxial Fe/ZnSe/FeCo magnetic tunnel junctions have been grown on ZnSe(001) buffered GaAs(001) substrates by molecular beam epitaxy. Alloying a small amount of Co with Fe in the base electrode provides a better seed epilayer for the growth of the ZnSe barrier compared to pure Fe as seen by transmission electron microscopy. Detailed characterization of the FeCo surface was performed by in situ scanning tunneling microscopy and revealed pyramid-shaped defects of up to 60 Å in height distributed on the FeCo surface. Transport measurements on microfabricated tunnel junctions yielded up to 16% magnetoresistance at 10 K and the effect is attributed to spin polarized tunneling across the semiconductor barrier in the energy range of the gap. The observed anomalous character of the magnetoresistance was attributed to conduction through the pyramidal defects in the base FeCo layer.
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| 6. |
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| 7. |
- Marangolo, M, et al.
(författare)
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Magnetism of the Fe/ZnSe(001) interface
- 2002
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 88:21, s. 217202-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetism of epitaxial ultrathin films of Fe on ZnSe(001) has been investigated by x-ray magnetic circular dichroism down to the submonolayer regime. In contrast to other metallic ferromagnet/semiconductor interfaces, no reduction of the Fe magnetic moment was found at the Fe/ZnSe(001) interface. Furthermore, a significant enhancement of the Fe magnetic moment compared to the bulk value was observed for coverages up to one monolayer in agreement with theoretical predictions. We also demonstrate that the magnetic properties of the Fe/ZnSe(001) interface remain stable against thermal annealing up to 300 degrees C, a prerequisite for the future development of efficient spintronics devices.
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| 8. |
- Tacchi, S., et al.
(författare)
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Epitaxial Fe films on ZnSe(001): effect of the substrate surface reconstruction on the magnetic anisotropy
- 2012
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 24:23, s. 236006-
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that Fe films deposited on a c(2 x 2)-reconstructed ZnSe(001) surface show a strong in-plane uniaxial magnetic anisotropy. Here, the effect of the substrate reconstruction on the magnetic anisotropy of Fe has been studied by in situ Brillouin light scattering. We found that the in-plane uniaxial anisotropy is strongly reduced for Fe films grown on a (1 x 1)-unreconstructed ZnSe substrate while the in-plane biaxial one is nearly unaffected by the substrate reconstruction. Calculations of magnetic anisotropy energies within the framework of ab initio density functional theory reveal that the strong suppression of anisotropy at the (1 x 1) interface occurs due to complex atomic relaxations as well as the competing effects originating from magnetocrystalline anisotropy and dipole-dipole interactions. For both sharp and intermixed c(2 x 2) interfaces, the magnetic anisotropy is enhanced compared to the (1 x 1) case due to the further lowering of symmetry. The theoretical results are in agreement with the experimental findings.
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