arXiv:1001.2449v1  [cond-mat.mtrl-sci]  14 Jan 2010
Exchange bias of a ferromagnetic semiconductor by a ferromagnetic metal
K. Olejnik, 1, 2 P. Wadley,3 J. Haigh, 3 K. W. Edmonds, 3 R. P. Campion, 3 A. W. Rushforth, 3 B. L. Gallagher, 3
C. T. Foxon, 3 T. Jungwirth, 2, 3 J. Wunderlich,1, 2 S. S. Dhesi, 4 S. Cavill, 4 G. van der Laan, 4 and E. Arenholz 5
1Hitachi Cambridge Laboratory, Cambridge CB3 0HE, United Kingdom
2Institute of Physics ASCR, v.v.i., Cukrovarnicka 10, 16253Praha 6, Czech Republic
3School of Physics and Astronomy, University of Nottingham,Nottingham NG7 2RD, United Kingdom
4Diamond Light Source, Harwell Science and Innovation Campus,
Didcot, Oxfordshire, OX11 0DE, United Kingdom
5Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
(Dated: August 24, 2018)
We demonstrate an exchange bias in (Ga,Mn)As induced by anti ferromagnetic coupling to a thin
overlayer of Fe. Bias ﬁelds of up to 240 Oe are observed. Using element-speciﬁc x-ray magnetic
circular dichroism measurements, we distinguish a strongl y exchange coupled (Ga,Mn)As interface
layer in addition to the biassed bulk of the (Ga,Mn)As ﬁlm. Th e interface layer remains polarized
at room temperature.
PACS numbers: 75.70.Cn, 75.50.Pp, 75.50.Bb
Ferromagnetic (FM) semiconductors oﬀer the prospect
of combining high-density storage and gate-controlled
logic in a single material. The realization of spin-valve
devices from FM semiconductors requires the controlled
switching of magnetization in adjacent layers between
antiferromagnetic (AFM) and FM conﬁgurations. This
has motivated several theoretical investigations of inter-
layer coupling in all-semiconductor devices1, and AFM
coupling has recently been demonstrated in (Ga,Mn)As
multilayers separated byp-type non-magnetic spacers 2.
However, the Curie temperature TC of (Ga,Mn)As is
currently limited to 185 K in single layers 3, and is
typically much lower for layers embedded within a
heterostructure2, which is an obstacle to the practical
implementation of semiconductor spintronics.
The development of FM metal/FM semiconductor het-
erostructures has the potential to bring together the
beneﬁts of metal and semiconductor based spintron-
ics, oﬀering access to new functionalities and physi-
cal phenomena. Recent studies of MnAs/(Ga,Mn)As
and NiFe/(Ga,Mn)As bilayer ﬁlms have shown FM in-
terlayer coupling and independent magnetization be-
havior, respectively4,5. Of particular interest is the
Fe/(Ga,Mn)As system, since the growth of epitaxial
Fe/GaAs(001) ﬁlms is well-established6. Remarkably, a
recent x-ray magnetic circular dichroism (XMCD) study
has shown that Fe may induce a proximity polariza-
tion in the near-surface region of (Ga,Mn)As, antipar-
allel to the Fe moment and persisting even above room
temperature7. Devices incorporating Fe/(Ga,Mn)As
therefore oﬀer the prospect of obtaining non-volatile
room temperature spin-polarization in a semiconductor.
Until now, no information has been revealed about the
coupling of Fe to (Ga,Mn)As layers away from the near-
surface region. At the surface, the (Ga,Mn)As layer may
be highly non-stoichiometric and Mn-rich, due to its non-
equilibrium nature8,9. Previously, Fe/(Ga,Mn)As layers
were produced by a process including exposure to air fol-
lowed by sputtering and annealing prior to Fe deposition,
which may further disrupt the interface order. The ori-
gin of the interface magnetism then had to be inferred by
comparison to a series of reference samples7. Demonstra-
tion of coupling between the bulk of the layers, i.e., an
exchange bias eﬀect, would provide direct evidence of the
interface magnetic order. Moreover, such coupling would
oﬀer new means of manipulating the FM semiconductor
spin state and utilizing the proximity polarization eﬀect
in a spintronic device.
Here, we demonstrate an antiferromagnetic coupling
and exchange bias in Fe/(Ga,Mn)As bilayer ﬁlms, by
combining element-speciﬁc XMCD measurements and