3
samples15, the projected Mn 3 d magnetic moments are
obtained as −1.4 µB and +0.8 µB per ion at remanence
and 1000 Oe, respectively.
The diﬀerence between these values can be understood
as being due to an interface layer which is strongly anti-
ferromagnetically coupled to the Fe layer. At zero ﬁeld,
both the interfacial and bulk Mn are aligned antiparallel
to the Fe layer. At high ﬁelds, the bulk of the (Ga,Mn)As
layer away from the interface is re-oriented into the exter-
nal ﬁeld direction. However, the interfacial Mn remains
antiparallel to the Fe layer and thus partially compen-
sates the XMCD signal from the bulk of the (Ga,Mn)As.
From the size of the remanent and 1000 Oe magnetic
moments, it can be estimated that around 25-30% of the
TEY XMCD signal can be ascribed to the interfacial Mn
which is strongly coupled to the Fe moments.
The interfacial Mn moments are ascribed to the prox-
imity polarization of the (Ga,Mn)As interface by the Fe
layer, such as was shown previously by XMCD as well as
ab initiotheory7. Evidence for this can be observed from
measurement of the Mn L2,3 XMCD signal at tempera-
tures above the (Ga,Mn)As TC . Similar to the previous
study7, we observe a small but not negligible signal at
room temperature (Fig. 3), with opposite sign to the Fe
L2,3 XMCD. Its spectral shape is characteristic of a local-
ized electronic conﬁguration close to d5, similar to bulk
(Ga,Mn)As7,9,15 but in contrast to Mn in more metallic
environments such as Mn xFe1−x7 or MnAs 16. A slight
broadening is observed on the low energy side of the Mn
L3 peak, which may be due to the diﬀerent screening in-
duced by proximity to the Fe layer. Since the measured
intensity is attenuated with distancez from the surface
as I = I0 exp(−z/λ T EY), the thickness of the strongly
coupled interface layer is estimated to be ∼0.7 nm or 2-3
monolayers, assuming a uniform distribution of Mn ions
and magnetic moments throughout the (Ga,Mn)As ﬁlm.
This is around a factor of three thinner than in Ref.7,
which could be due to the lower Mn concentration or the
diﬀerent preparation method of the present samples.
In summary, we have demonstrated antiferromagnetic
coupling between Fe and (Ga,Mn)As layers in bilayer
structures. A markedly diﬀerent coupling is observed for
the bulk of the (Ga,Mn)As layer and for Mn moments
in the near-interface region. A thickness-dependent ex-
change bias ﬁeld is observed to aﬀect the whole of the
bulk (Ga,Mn)As layer, which aligns antiparallel to the
Fe layer at low ﬁelds, and switches to parallel when the
external ﬁeld is large enough to overcome the bias ﬁeld
and the magnetocrystalline anisotropy ﬁelds. In contrast,
the interfacial Mn moments remain aligned antiparallel
to the Fe layer even at 20 kOe, the largest ﬁeld studied,
and are polarized at temperatures well above theTC of
the bulk (Ga,Mn)As layer. The latter observation con-
ﬁrms the recently reported result of Ref. 7, in which
the Fe/(Ga,Mn)As bilayers were produced by a diﬀerent
method but showed qualitatively similar behavior of the
interfacial moments. Our results shed new light on the
magnetic coupling in Fe/(Ga,Mn)As hybrid layers which
are of potential interest for room temperature spintron-
ics, and also oﬀer a means of controlling the spin orien-
tation in a FM semiconductor.
We acknowledge support from EU grants
SemiSpinNet-215368 and NAMASTE-214499, and
STFC studentship grant CMPC07100. The Advanced
Light Source is supported by the U.S. Department of
Energy under Contract No. DE-AC02-05CH11231.
We thank Leigh Shelford for help during the Diamond
beamtime.
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