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Exchange bias and asymmetric magnetization reversal in ultrathin Fe films grown on GaAs (001) substrates
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Image of FIG. 1.
FIG. 1.

Atomic arrangement at the GaAs/Fe interface for an As-terminated unreconstructed GaAs (001) face and the epitaxial bcc Fe. The crystallographic orientations are indicated on the left of the figure.

Image of FIG. 2.
FIG. 2.

Magnetic hysteresis loops for the Fe film (sample A) observed at a series of temperatures for magnetic field applied along the [110] crystallographic direction.

Image of FIG. 3.
FIG. 3.

Measured temperature dependence of the exchange bias field HE and coercivity field H C of the GaAs/Fe/Au film (sample A). The blocking temperature (TB) is estimated as ∼25 K.

Image of FIG. 4.
FIG. 4.

Coordinate system used in the experiments. The applied magnetic field is kept in the plane of the Fe film. Orientations of crystal faces are shown on the sides of the structure.

Image of FIG. 5.
FIG. 5.

Magnetic hysteresis loops of the Fe film for the external field H applied at a series of azimuthal angles φH measured from the [110] direction, as shown in Fig. 4 . The panels on the left show the hysteresis loops observed at 5 K in the ZFC mode. Panels on the right show simulations of the magnetic hysteresis loops for the four angles φH . used in the experiments.

Image of FIG. 6.
FIG. 6.

Double hysteresis loops of two GaAs/Fe/Au samples (samples D and E, respectively) measured at 5 K after zero-field cooling (ZFC), indicating the presence of two independent populations of AFM orderings, which pin two populations of FM domains. “S” indicates the point where the first training loop (indicated by black curve) begins.

Image of FIG. 7.
FIG. 7.

X-ray reflectivity data for a typical GaAs/Fe/Au multilayer grown on a GaAs (001) substrate. Black curve is experimental; red curve is a computer fit obtained with interfacial layers assumed to be GaAs/Fe2As/Fe/FeO/Au. The thicknesses of the successive layers d obtained from the best fit are as follows: dFe(2)As = 0.73 ± 0.19 nm, dFe = 3.65 ± 0.48 nm, dFeO = 1.4 ± 0.48 nm, and dAu = 1.72 ± 0.36 nm. The data and modeling start at angles just below the critical angle of 0.3°.

Image of FIG. 8.
FIG. 8.

Fe L2,3 XAS spectra recorded at room temperature for Fe/GaAs with two different capping layers: The blue curve is for sample A capped by ∼2 nm Au layer, and the red curve is for a sample coated by ∼2 nm Al.

Image of FIG. 9.
FIG. 9.

Comparison of magnetic hysteresis loops observed for GaAs/Fe/Au multilayer at (a) 5 K and (b) 25 K; and (c) for a GaAs/Fe/Al multilayer observed at 5 K.

Image of FIG. 10.
FIG. 10.

Hysteresis loops for sample D (shown in the upper panel of Fig. 6 ), observed after field cooling in +2.0 and −2.0 kOe. Field cooling results in disappearance of the double loop seen in Fig. 6 .


Generic image for table
Table I.

Structural and magnetic parameters of five GaAs/Fe/Au samples studied in the present work. Note that the thicknesses of Fe and Au are estimated from the ion current of the e-beam evaporator, which has a large uncertainty. The thicknesses of the layers are estimated from the growth rate with the error of around 5% for LT-GaAs, and of around 30% for the Fe and Au layers due to possible flux instabilities of the e-beam evaporator.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Exchange bias and asymmetric magnetization reversal in ultrathin Fe films grown on GaAs (001) substrates