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Surface morphology and atomic structure of thin layers of Fe3Si on GaAs(001) and their magnetic properties
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View: Figures


Image of FIG. 1.
FIG. 1.

Model of the D03 unit cell of Fe3Si. Two of the fcc sublattices are occupied by FeA atoms. The other sublattices are occupied by FeB and Si, respectively.

Image of FIG. 2.
FIG. 2.

STM images of GaAs(001) substrates. The left hand side shows a Ga-rich (4 × 2)- and (2 × 6)-reconstructed surface obtained after cycles of sputtering and annealing at 500 °C. The scan on the right hand side shows an As-rich (2 × 4)-reconstructed surface. The insets are the corresponding LEED patterns.

Image of FIG. 3.
FIG. 3.

Overview STM scan of 12 ML of Fe3Si deposited on GaAs(001) after post annealing at 300 °C. For comparison, the inset shows the surface directly after the deposition with TG = 200 °C. The right hand side shows a linescan across a terrace and the corresponding LEED pattern (107 eV).

Image of FIG. 4.
FIG. 4.

Left: STM scan after post annealing a 12 ML silicide layer at 400 °C. Right: Larger scale image by SEM (ex-situ) detecting secondary electrons after post annealing at 500 °C. The black and white circles indicate regions where an alloying between the Fe3Si layer and the GaAs substrate has taken place.

Image of FIG. 5.
FIG. 5.

RMS roughnesses as a function of the post annealing temperature. The values were determined from an area of (100 nm)2, and the error bars represent the standard deviation from the mean value. The roughnesses at 400 °C and 500 °C connected by the dashed red lines were measured in areas without cavities.

Image of FIG. 6.
FIG. 6.

STM scan showing the surface morphology after the deposition of 13 ML Fe3Si at TG = 250 °C. The inset shows the corresponding LEED pattern (48 eV) where both spots of the D03 structure (a) and spots of the reconstructed substrate surface (b) can be observed.

Image of FIG. 7.
FIG. 7.

STM scan revealing the atomic structure using a cyclic grey scale to enhance the atomic contrast across several terraces. The inset is a zoom-in which points out two types of antisite defects indicated by the dotted black and white crosslines. The atomic model is meant for orientation in order to determine the position of the antisite defects.

Image of FIG. 8.
FIG. 8.

STM scans showing examples for regular stacking sequences (left) and faulted stacking sequences (right) again using a cyclic grey scale. In the first case, the dashed lines lie exactly between two atomic rows for one terrace level and on top of the atomic row for the next level. This shift is not observed in the second case representing faulted stacking. Furthermore, the dotted horizontal line indicates that shifts also occur within one layer thus implying the existence of in-plane antiphase boundaries.

Image of FIG. 9.
FIG. 9.

Overview STM scan of 2 ML of Fe3Si deposited on GaAs(001) using the identical preparation conditions as for the layer in Figure 3 . The inset on the left hand side shows a close-up scan while the inset on the right hand side shows the corresponding LEED pattern (135 eV) with D03 structure related spots (a) but also traces remaining from the substrate surface reconstruction (b). The small squares (for better visualization an array rather than a single square is shown) illustrate the effective size of the superparamagnetic clusters of this structure which will be discussed in the following section.

Image of FIG. 10.
FIG. 10.

Left: MOKE hysteresis loops of a 12 ML sample annealed at 300 °C measured in-situ for different crystallographic directions. Right: Polar plot of the normalized remanences.

Image of FIG. 11.
FIG. 11.

Left: Magnetization loop of 2 ML Fe3Si/GaAs(001) as measured by SQUID magnetometry at 300 K. The inset shows the small opening of the hysteresis around zero. The solid line is the Langevin function fitted to this data. Right: ZFC-FC-curve of the same sample (H = 20 Oe, ΔT/Δt = 2 K/min).

Image of FIG. 12.
FIG. 12.

Left: MOKE hysteresis loops of a 60 ML sample for different crystallographic directions. Right: Polar plot of the normalized remanences.

Image of FIG. 13.
FIG. 13.

Average magnetic moment per atom at room temperature as a function of the Fe3Si layer thickness. The error bars mainly originate from the error when determining the area of the samples. The dashed line indicates the value of bulk Fe3Si. The insets show corresponding STM overview scans for 5 ML and 10 ML.

Image of FIG. 14.
FIG. 14.

Fits of the angular dependent resonance fields for the considered layer thicknesses as measured by FMR. The values of the x-axis refer to the angle between the [110] direction and the measurement direction. The general trend from a uniaxial anisotropy at low thicknesses towards a fourfold anisotropy at higher thicknesses can directly be observed.

Image of FIG. 15.
FIG. 15.

Thickness dependence of the magnetocrystalline anisotropy constant.

Image of FIG. 16.
FIG. 16.

Thickness dependent linewidths obtained from the FMR spectra.

Image of FIG. 17.
FIG. 17.

Thickness dependence of the in-plane uniaxial anisotropy plotted versus the thickness d and 1/d in the inset.

Image of FIG. 18.
FIG. 18.

Thickness dependence of the out-of-plane anisotropy.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Surface morphology and atomic structure of thin layers of Fe3Si on GaAs(001) and their magnetic properties