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Register a new userKinetic stabilization of Fe film on (4 by 2)-GaAs(100)
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We grow Fe film on (4 by 2)-GaAs(100) at low temperature, (~ 130 K) and study their chemical structure by photoelectron spectroscopy using synchrotron radiation. We observe the effective suppression of As segregation and remarkable reduction of alloy formation near the interface between Fe and substrate. Hence, this should be a way to grow virtually pristine Fe film on GaAs(100). Further, the Fe film is found stable against As segregation even after warmed up to room temperature. There only forms very thin, ~ 8 angstrom thick interface alloy. It is speculated that the interface alloy forms via surface diffusion mediated by interface defects formed during the low temperature growth of the Fe film. Further out-diffusion of both Ga and As are suppressed because it should then proceed via inefficient bulk diffusion.
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We study the growth of the Fe films on GaAs(100) at a low temperature, 140 K, by $in$-$situ$ UHV x-ray reflectivity using synchrotron radiation. We find rough surface with the growth exponent, $beta_S$ = 0.51$pm$0.04. This indicates that the growth of the Fe film proceeds via the restrictive relaxation due to insufficient thermal diffusion of the adatoms. The XRR curves are nicely fit by a model with a uniform Fe film, implying that the surface segregation and interface alloying of both Ga and As are negligible. When the Fe film is annealed to 300 K, however, the corresponding XRR can be fit only after including an additional layer of 9 A thickness between the Fe film and the substrate, indicating the formation of ultrathin alloy near the interface. The confinement of the alloy near the interface derives from the fact that the diffusion of Ga and As from the substrate should proceed via the inefficient bulk diffusion, and hence the overlying Fe film is kinetically stabilized.
Nanoscale Fe3O4 epitaxial thin film has been synthesized on MgO/GaAs(100) spintronic heterostructure, and studied with X-ray magnetic circular dichroism (XMCD). We have observed a total magnetic moment of (3.32 +- 0.1) uB/f.u., retaining 83% of the bulk value. Unquenched orbital moment of (0.47 +- 0.05) uB/f.u. has been confirmed by carefully applying the sum rule. The results offer direct experimental evidence of the bulk-like total magnetic moment and a large orbital moment in the nanoscale fully epitaxial Fe3O4/MgO/GaAs(100) heterostructure, which is significant for spintronics applications.
Spin wave frequencies are observed in ultra-thin Fe/GaAs(100) films at temperatures where the spontaneous zero field magnetization is zero. The films exhibit good cyrstalline structure, and the effect of magnetic anisotropies is apparent even though no zero field spin wave energy gap exists. An analysis is given in terms of a superparamagnetic model in which the film is treated as a network of non-interacting single domain magnetic islands. A spin wave analysis provides a means to separate measured values of anisotropy parameters from products involving anisotropy and island volume. In this way, a measure of the activation volume associated with superparamagnetic islands is obtained for different Fe film thicknesses. Results suggest that the island lateral area increases with increasing film thickness.
Fe3Si/Al/Fe3Si/GaAs(001) structures were deposited by molecular-beam epitaxy and characterized by transmission and scanning electron microscopy, and x-ray diffraction. The first Fe3Si film on GaAs(001) is growing epitaxially as (001) oriented single crystal. The subsequent Al film grows almost 111 oriented in a fibre texture although the underlying Fe3Si is exactly (001) oriented. The growth in this orientation is triggered by a thin transition region which is formed at the Fe3Si/Al interface. In the end after the growth of the second Fe3Si layer on top of the Al the final properties of the whole stack depend on the substrate temperature T_S during deposition of the last film. The upper Fe3Si films are mainly 110 oriented although they are poly-crystalline. At lower T_S, around room temperature, all the films retain their original structural properties.
We present an investigation of the magnetic behavior of epitaxial MnAs films grown on GaAs(100). We address the dependence of the magnetic moment, ferromagnetic transition temperature ($T_c$) and magnetocrystalline anisotropy constants on epitaxial conditions. From thorough structural and magnetic investigations, our findings indicate a more complex relationship between strain and magnetic properties in MnAs films than a simple stretch/compression of the unit cell axes. While a small increase is seen in the anisotropy constants the enhancement of the magnetic moment at saturation is significant. X-ray magnetic circular dichroism results show a behavior of the spin- and orbital-moment which is consistent with a structural transition at $T_c$. In particular, we find that the ratio of the orbital to spin moment shows a marked increase in the coexistence region of the ferromagnetic $alpha$- and paramagnetic $beta$-phases, a result that is well in accord with the observed increase of the $c/a$-ratio in the same temperature region. The textit{ab initio} density functional calculations reveal that the magnetic properties are more sensitive towards change in in-plane axis as compared to a change of the out-of-plane axis, which is explained by the analysis of band structures. The effects of electron correlation in MnAs using textit{ab initio} dynamical mean field theory are also presented.
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