2
measurements were performed on beamline I06 at the
Diamond Light Source, and on beamline 4.0.2 at the Ad-
vanced Light Source. Total-electron yield (TEY) and
ﬂuorescence yield (FY) were monitored simultaneously
using the sample drain current and the photocurrent of a
diode mounted at 90◦ to the incident beam, respectively.
SQUID magnetometry measurements were
ﬁrst performed on control Fe/GaAs(001) and
(Ga,Mn)As/GaAs(001) samples, grown under the
same conditions as the bilayers, to determine the
magnetic anisotropies of the individual layers and the
Curie temperature of the (Ga,Mn)As layer. The Fe ﬁlm
has a uniaxial magnetic anisotropy with easy axis along
the [110] orientation, similar to previous studies6. For
the (Ga,Mn)As control sample, there is a competition
between cubic and uniaxial magnetic anisotropies, with
the former dominant at low temperatures and favoring
easy axes along the in-plane⟨100⟩ orientations, and the
latter dominant close to TC (∼35 K) giving an easy axis
along the [1 ¯
10] orientation. Figure 1 shows [110] magne-
tization versus temperature curves and low temperature
hysteresis loops for a bilayer ﬁlm containing a 20 nm
thick (Ga,Mn)As layer. The total remnant moment of
the bilayer ﬁlm decreases on cooling under zero magnetic
ﬁeld below theTC of the (Ga,Mn)As, indicating that
this layer aligns antiparallel to the Fe magnetization
at zero ﬁeld. The hysteresis curve shows a two-step
magnetization reversal, indicating diﬀerent behavior of
the Fe and (Ga,Mn)As layers, with the smaller loop
attributed to the dilute moment (Ga,Mn)As ﬁlm. The
minor hysteresis loop shown in Fig. 1 clearly shows a
shift from zero ﬁeld by a bias ﬁeldHE , indicating that
the Fe layer induces an exchange bias in the magnetic
semiconductor. The shape and size of the minor loop
is in agreement with the hysteresis loop for the control
(Ga,Mn)As sample, also shown in Fig. 1. This strongly
indicates that the exchange bias aﬀects the whole of the
(Ga,Mn)As layer in the bilayer sample.
Similar behavior is observed for bilayer samples con-
taining a 10 nm or 50 nm (Ga,Mn)As layer, with a
bias ﬁeld which is approximately inversely proportional
to the thicknessd of the ferromagnetic semiconductor
layer (Fig. 1, inset). This 1/ d dependence of HE was
found previously for MnAs/(Ga,Mn)As bilayers 4, and
is generally observed in exchanged-biased thin ﬁlms 12.
From this dependence it is possible to describe the ex-
change bias in terms of an interface energy per unit area,
∆E = MF SHE d = 0 . 003 erg/cm 2. This value is rather
small compared to typical exchange bias systems 12, re-
ﬂecting the low moment density MF S of the diluted
FM semiconductor layer. However, the bias ﬁeld for a
given (Ga,Mn)As thickness is larger than is observed for
MnO/(Ga,Mn)As structures13, while the reproducibility
and ﬂexibility of the present structures is much higher
due to the single-crystalline ferromagnetic nature of the
Fe layer.
To conﬁrm the presence of AFM interlayer coupling,
we performed XMCD measurements at the Mn and Fe
L2,3 absorption edges in order to determine the magnetic
response of the individual elements. In L2,3 XMCD, elec-
trons are excited from a 2 p core level to the unoccupied
3d valence states of the element of interest by circularly
polarized x-rays at the resonance energies of the transi-
tions. The diﬀerence in absorption for opposite polariza-
tions gives a direct and element-speciﬁc measurement of
the projection of the 3d magnetic moment along the x-
ray polarization vector. The absorption cross-section is
conventionally obtained by measuring the decay products
– either ﬂuorescent x-rays or electrons – of the photoex-
cited core hole. The type of decay product measured
determines the probing depth of the technique. For Mn
L2,3 absorption, the probing depths for FY and TEY de-
tection are λF Y ≈ 100 nm and λT EY ≈ 3 nm. In the
current experiment, the Mn XMCD measured using FY
and TEY are thus sensitive to the bulk of the (Ga,Mn)As