Applied
Surface
Science
258 (2012) 8965–
8969
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at
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Applied
Surface
Science
j
our
nal
ho
me
p
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www.elsevier.com/loc
ate/apsusc
Single
crystalline
Cr
2
O
3
nanowires/nanobelts:
CrCl
3
assistant
synthesis
and
novel
magnetic
properties
Shuhu
Yang
a
,
Shijiang
Liu
b
,
Changyong
Lan
a
,
Shaoguang
Yang
a,∗
a
National
Laboratory
of
Microstructure
and
Department
of
physics,
Nanjing
University,
Nanjing
210093,
China
b
College
of
Physics
and
Electronic
Information,
Luoyang
Normal
College,
Luoyang
471022,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
22
January
2012
Received
in
revised
form
23
April
2012
Accepted
23
May
2012
Available online 1 June 2012
Keywords:
Cr
2
O
3
Nanowire/nanobelt
Chloride
assistant
growth
Néel
temperature
a
b
s
t
r
a
c
t
Large
amounts
of
single
crystalline
Cr
2
O
3
nanowires/nanobelts
were
obtained
using
CrCl
3
assistant
syn-
thesis
method.
Scanning
electron
microscopy
and
transmission
electron
microscopy
results
showed
the
nanowire/nanobelt
morphology
of
the
product.
X-ray
diffraction
and
high
resolution
transmission
elec-
tron
microscopy
illustrated
the
formation
of
the
alumina
phase
Cr
2
O
3
nanowires/nanobelts.
A
new
growth
mechanism
of
the
nanowires/nanobelts
is
proposed
and
discussed.
Zero
field
and
field
cooled
tempera-
ture
dependence
of
magnetization
measurements
of
the
nanowires/nanobelts
showed
clear
decrease
of
the
Néel
temperature
compared
to
their
bulk
forms,
which
is
attributed
to
size
and
surface
effect
of
the
Cr
2
O
3
nanowires/nanobelts.
© 2012 Elsevier B.V. All rights reserved.
1.
Introduction
One
dimensional
(1D)
nanostructures,
such
as
nanowires,
nanobelts,
and
nanotubes,
have
attracted
much
attention
in
recent
years
due
to
their
fascinating
properties
and
promising
technolog-
ical
applications
related
to
lasers,
generators,
spintronics,
biology,
and
medicine,
etc.
[1–6].
Among
these
materials,
1D
nanostruc-
tured
antiferromagnetic
(AFM)
transition
metal
oxides
have
been
of
particular
interests
for
data
storage
and
spin-valve
devices
[7].
These
nanostructures
can
be
quite
different
from
those
of
their
bulk
forms
due
to
the
size
and
surface
effect,
which
would
show
spin-
glass
like
behavior,
exchange
bias
effect
[1,7–9],
and
the
variation
of
their
Néel
temperatures
(magnetic
phase
transition
temperature
between
AFM
and
paramagnetism
(PM))
[10–13].
Among
the
transition
metal
oxides,
Cr
2
O
3
is
a
very
important
material,
which
has
been
widely
used
as
a
green
pigment,
coating
material
for
thermal
protection,
refractory
material
due
to
its
high
melting
temperature
of
about
2710
K,
oxidative
resistance
[14,15],
and
heterogeneous
catalyst
[16],
etc.
Moreover,
bulk
Cr
2
O
3
is
an
important
insulating
AFM
material
with
a
Néel
temperature
of
about
307
K
and
is
suitable
for
using
as
tunnel
junction
barrier.
On
the
other
hand,
much
effort
has
been
done
to
the
synthesis
of
Cr
2
O
3
nanostructures
due
to
the
expected
novel
properties
and
potential
applications.
Most
researches
are
focused
on
the
synthe-
sis
and
magnetic
properties
of
nanoparticles
[17–19].
In
contrast,
∗
Corresponding
author.
Tel.:
+86
25
83597483;
fax:
+86
25
83595539.
E-mail
address:
sgyang@nju.edu.cn
(S.
Yang).
there
are
few
reports
concerning
with
the
synthesis
of
1D
Cr
2
O
3
nanostructures,
and
most
of
the
materials
synthesized
there
are
polycrystalline
1D
Cr
2
O
3
nanostructures
with
the
use
of
templates
[20–22].
To
the
best
of
our
knowledge,
template
free
synthesis
of
1D
single
crystalline
Cr
2
O
3
has
only
been
reported
by
Han
et
al.
[23].
However,
the
nanobelts
and
nanorods
they
obtained
are
not
dense
enough
and
no
magnetic
properties
are
reported
in
their
paper
[23].
The
synthesis
of
large
amount
of
1D
single
crystalline
Cr
2
O
3
nanostructures
is
still
a
challenge.
In
the
present
work,
we
report
a
convenient
new
template
free
synthesis
method
to
obtain
large
amount
of
single
crystalline
Cr
2
O
3
nanowires/nanobelts
in
a
short
time
(15
min)
using
Cr
foil
as
starting
materials.
And
the
field
and
temperature
dependences
of
magnetization
of
the
single
crystalline
nanowires/nanobelts
are
investigated.
2.
Experimental
Single
crystalline
Cr
2
O
3
nanowires/nanobelts
were
synthesized
using
Cr
foil
and
CrCl
3
as
starting
materials,
and
N
2
flow
was
used
as
carrier
gas.
The
typical
process
is
as
follows:
Cr
foils
were
washed
in
ethanol
after
polished
mechanically.
Then
the
foil
was
put
in
the
center
of
the
quartz
tube
placed
inside
a
horizontal
furnace
and
appropriate
amount
of
CrCl
3
was
put
in
upstream
of
the
tube,
5
cm
away
from
the
Cr
foil.
A
Y-shape
three-way
connection
was
used
to
control
the
gas
to
go
directly
or
through
the
water
to
the
quartz
tube.
The
furnace
was
heated
with
a
constant
pure
N
2
flow
of
100
sccm.
When
the
furnace
temperature
reached
600
◦
C,
a
wet
N
2
gas
of
100
sccm,
which
was
passed
through
the
de-ionized
water
bubbler
maintained
at
a
temperature
of
50
◦
C,
was
supplied
0169-4332/$
–
see
front
matter ©
2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.apsusc.2012.05.129