Magnetic, electrical and optical properties of p-type Fe-doped CuCrO
2
semiconductor thin films
Fangting Lin
⇑
, Cai Gao, Xiaoshan Zhou, Wangzhou Shi, Aiyun Liu
Key Laboratory of Optoelectronic Material and Device, and Department of Physics, Shanghai Normal University, Shanghai 200234, PR China
article info
Article history:
Received 14 May 2013
Received in revised form 23 July 2013
Accepted 23 July 2013
Available online 31 July 2013
Keywords:
Semiconductors
Magnetic films and multilayers
Microstructure
Magnetization
Electrical transport
Optical properties
abstract
Fe-doped CuCrO
2
delafossite thin films, with a c-axis quasi-epitaxial orientation, were prepared by pulsed
laser deposition, exhibiting reasonably good p-type conductivity, ferromagnetism with T
C
well above
room temperature, and comparatively high transparency in the visible range. The influence of Fe concen-
tration (0–15 at%) on microstructure and physical properties was investigated. The substitution of Fe
3+
for Cr
3+
induces the lattice expansion, which is favorable for the oxygen insertion and thus produces
the higher hole concentration. Accordingly the p-type conductivity is remarkably improved to 28 S cm
1
.
Moreover, the introduction of Fe
3+
leads to the hole-mediated Fe
3+
–Cr
3+
super-exchange coupling respon-
sible for the room-temperature ferromagnetism. The saturation magnetization is enhanced as the Fe con-
centration increases, with Curie temperature P550 K. Nevertheless, the transparency in the visible range
does not profit from the Fe doping. The transmittance is diminished from 75% for x = 0 to 65% for
x = 15 at% at the wavelength of 750 nm, which can be interpreted as the strengthened scattering of pho-
tons by charge carriers. The direct optical bandgap is modulated by 3.8% via the Fe addition. The results
show that the substitution of iron for chromium is an effective way to achieve high-performan ce CuCrO
2
thin films which are supposed to become a promising p-type transparent diluted magnetic semiconduc-
tor material.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
There has been great interest in oxide-based diluted magnetic
semiconductors (DMSs) due to their unique magnetic, magneto-
electrical, magneto-optical effects and high transparency in the
visible region. Potential applications are shown in the fields of
spintronic devices and transparent optoelectronic devices, such
as spin-valve transistors, spin light-emitting diodes, nonvolatile lo-
gic devices, transparent electrodes in flat panel displays, and win-
dow layers in solar cells. However, some key issues urgently need
to be solved, e.g. low Curie temperature (T
C
), small magnetization,
easy formation of ferromagnetic impurities and controversial ori-
gin of magnetism.
In terms of theoretical calculations [1–3], ferromagnetic cou-
pling between magnetic ions could be formed more easily in p-
type semiconductors due to hole carriers serving as a medium.
Consequently, the delafossite (ABO
2
) structure, a typical p-type
transparent conducting oxide (TCO), has drawn extensive attention
in recent years. Kizaki et al. predicted that Cu(Al
1x
TM
x
)O
2
(TM =V,
Cr, Mn, Fe, Ni) would show ferromagnetism for which the double-
or super-exchange interaction was responsible [4]. Later, room-
temperature ferromagnetism was realized in Cu(Al
1x
Co
x
)O
2
films
[5]. For another delafossite family, Cu(Cr
1x
M
x
)O
2
(M =Mn[6],Ni
[7,8],Al[9],Rh[10],Co[11]) ceramics were fabricated succes-
sively, exhibiting low-temperature ferromagnetism. It was argued
that the trivalent dopants could destabilize the anti-ferromagnetic
order of Cr
3+
ions. Furthermore, Wang et al. synthesized Cu(Cr
1x-
Mn
x
)O
2
thin films by chemical solution deposition and achieved
room-temperature ferromagnetism at the expense of electrical
conductivity [12]. It is demonstrated that B-site transition metal
doping is a possible way for p-type delafossite oxides to obtain fer-
romagnetic order.
The above findings are intriguing but still far from practical
applications. In particular, transparent spintronic devices desire
epitaxial thin-film materials that possess excellent magnetic, elec-
trical and optical features simultaneously. In this study, to our
knowledge, it is the first time that c-oriented Fe-doped CuCrO
2
thin
films have been prepared by pulsed laser deposition (PLD), which
exhibit room-temperature ferromagnetism, comparatively high
p-type conductivity and transparency for visible light. Here CuCrO
2
delafossite was selected as the matrix semiconductor because of its
highest conductivity (
r
= 220 S cm
1
) among all p-type TCOs [13],
which is beneficial to hole-mediated magnetic exchange mecha-
nism [1–3]. Besides, iron was chosen as the dopant due to the
resemblance between the radii of Fe
3+
and Cr
3+
[14]. In such a
way, the substitution can be realized more easily without the
0925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jallcom.2013.07.160
⇑
Corresponding author. Tel.: +86 21 64322726; fax: +86 21 64328894.
E-mail address: nounou7@163.com (F. Lin).
Journal of Alloys and Compounds 581 (2013) 502–507
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
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