The
role
of
Cu
codoping
on
the
Fe
metal
clustering
and
ferromagnetism
in
Fe-doped
In
2
O
3
films
Feng-Xian
Jiang
a
,
Qi
Feng
b
,
Zhi-Yong
Quan
a
,
Rong-Rong
Ma
a
,
S.M.
Heald
c
,
G.A.
Gehring
b
,
Xiao-Hong
Xu
a,
*
a
Key
Laboratory
of
Magnetic
Molecules
and
Magnetic
Information
Material,
Ministry
of
Education,
School
of
Chemistry
and
Materials
Science,
Shanxi
Normal
University,
Linfen
041004,
People’s
Republic
of
China
b
Department
of
Physics
and
Astronomy,
University
of
Sheffield,
Hicks
Building,
Sheffield
S3
7RH,
United
Kingdom
c
Advanced
Photon
Source,
Argonne
National
Laboratory,
Argonne,
IL
60439,
USA
1.
Introduction
Diluted
magnetic
semiconductors
(DMSs)
have
attracted
much
attention
for
their
potential
applications
in
spintronic
devices
[1–
3].
Fe-doped
In
2
O
3
DMSs
are
regarded
as
a
promising
candidate
for
future
spintronic
device
application
because
a
homogeneous
material
can
be
realized
due
to
the
high
solubility
of
Fe
in
the
In
2
O
3
host
lattice
(20%)
[4,5],
therefore
many
research
groups,
including
ourselves,
have
paid
more
attention
to
the
Fe-doped
In
2
O
3
system
[6–9].
Moreover,
Cu
has
been
used
as
a
dopant
or
codopants
in
DMSs
because
neither
metallic
Cu
nor
its
oxides
(CuO
and
Cu
2
O)
are
ferromagnetic
and
hence
could
exclude
the
possibility
that
the
ferromagnetism
originates
from
the
magnetic
impurities
brought
by
Cu
itself
[10,11].
Recently,
it
has
been
reported
that
adding
Cu
into
Fe-doped
In
2
O
3
DMSs
can
influence
their
magnetic
and
transport
properties
significantly.
For
example,
Yoo
and
co-workers
[4,5]
obtained
room
temperature
(RT)
ferromagnetism
in
Fe-doped
In
2
O
3
bulk
and
film
samples
by
co-doping
a
small
amount
of
Cu
(2
at.%),
which
creates
the
mixed
valence
cations,
i.e.,
Fe
2+
,
Fe
3+
,
necessary
for
the
ferromagnetism
and
charge
transport.
Ho
et
al.
[12]
found
that
the
RT
ferromagnetism
of
Fe-doped
In
2
O
3
bulk
was
reduced
by
additional
Cu
doping.
Although
few
attempts
have
been
made
to
explain
the
role
of
Cu
on
ferromagnetism
in
Fe-doped
In
2
O
3
[13],
the
fundamental
mechanism
regarding
the
contributions
of
Cu
codopant
toward
the
magnetic
ordering
of
In
2
O
3
-based
DMSs
is
far
from
clearly
understood.
In
this
letter
we
report
measurements
on
the
effects
on
the
RT
ferromagnetism
of
adding
3%
of
Cu
into
Fe-doped
In
2
O
3
films
prepared
by
pulsed
laser
deposition
(PLD).
In
order
to
explore
the
origin
of
ferromagnetism
in
this
specific
system
further,
we
studied
the
dependence
of
the
magnetism
on
the
film
thickness.
Interestingly,
we
find
that
the
magnetization
of
Fe-doped
In
2
O
3
films
was
independent
of
thickness
and
the
observed
ferromagne-
tism
was
almost
homogeneous
[9];
however
the
films
showed
obvious
thickness
dependent
magnetization
after
adding
Cu.
The
temperature
dependence
of
the
magnetization,
X-ray
absorption
fine
structure
(XAFS)
and
magnetic
circular
dichroism
(MCD)
results
demonstrate
that
adding
Cu
causes
Fe
metal
clusters
to
be
formed
in
the
doped
In
2
O
3
films
leading
to
the
inhomogeneous
ferromagnetism.
The
role
of
adding
Cu
on
the
formation
of
Fe
clusters
in
Fe-doped
In
2
O
3
DMSs
is
also
discussed.
2.
Experiments
The
(In
0.95
Fe
0.05
)
2
O
3
and
(In
0.92
Fe
0.05
Cu
0.03
)
2
O
3
films
were
grown
on
c-cut
sapphire
substrates
by
a
PLD
technique
from
their
corresponding
targets
with
thickness
varying
from
100
to
400
nm
Materials
Research
Bulletin
48
(2013)
3178–3182
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
25
December
2012
Received
in
revised
form
29
March
2013
Accepted
27
April
2013
Available
online
4
May
2013
Keywords:
A.
Oxides
B.
Laser
deposition
C.
XAFS
(EXAFS
and
XANES)
D.
Magnetic
properties
A
B
S
T
R
A
C
T
We
have
grown
room
temperature
ferromagnetic
Fe,
and
Fe,Cu-codoped
In
2
O
3
films
on
sapphire
substrates
by
pulsed
laser
deposition.
The
magnetization
of
the
Fe-doped
In
2
O
3
films
was
independent
of
the
thickness
and
the
observed
ferromagnetism
was
almost
homogeneous.
The
addition
of
Cu
caused
the
films
to
exhibit
obvious
thickness
dependent
magnetization
and
the
ferromagnetism
became
inhomogeneous.
The
temperature
dependence
of
the
magnetization,
X-ray
absorption
fine
structure
and
magnetic
circular
dichroism
data,
clearly
established
the
presence
of
Fe
metal
clusters
in
Fe,Cu-
codoped
In
2
O
3
films,
which
contribute
to
the
inhomogeneous
ferromagnetism.
ß
2013
Elsevier
Ltd.
All
rights
reserved.
*
Corresponding
author.
Tel.:
+86
357
2051706;
fax:
+86
357
2052468.
E-mail
address:
xuxh@dns.sxnu.edu.cn
(X.-H.
Xu).
Contents
lists
available
at
SciVerse
ScienceDirect
Materials
Research
Bulletin
jo
u
rn
al
h
om
ep
age:
ww
w.els
evier.c
o
m/lo
c
ate/mat
res
b
u
0025-5408/$
–
see
front
matter
ß
2013
Elsevier
Ltd.
All
rights
reserved.
http://dx.doi.org/10.1016/j.materresbull.2013.04.066
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