Structure, magnetic, and optical properties in Zn0.98- xCu0.02FexO diluted magnetic semiconductors

Article abstract of DOI:10.1002/pssa.200925456

Cu-doped and Cu, Fe codoped ZnO diluted magnetic semiconductors (DMSs) powders samples were synthesized by the sol-gel method. The X-ray diffraction (XRD) results showed the Zn_0.985Cu_0.02O and Zn _0.95Fe_0.03Cu

Full text of DOI:10.1002/pssa.200925456

Phys. Status Solidi A 207, No. 8, 1811–1814 (2010) / DOI 10.1002/pssa.200925456
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applications and materials science
Structure, magnetic, and optical
properties in Zn0.98ꢀxCu0.02FexO diluted magnetic
semiconductors
Huilian Liu, Jinghai Yang*, Zhong Hua, Yongjun Zhang, Lili Yang, and Dandan Wang
Physics College of Jilin Normal University, Siping, China
Received 1 September 2009, revised 10 March 2010, accepted 12 March 2010
Published online 21 April 2010
* Corresponding author: e-mail jhyang1@jlnu.edu.cn, Phone: þ86 434 3294566, Fax: þ86 434 3294566
Cu-doped and Cu, Fe codoped ZnO diluted magnetic semi- magnetization of Zn0.98Cu0.02O DMSs increased after Fe
conductors (DMSs) powders samples were synthesized by the doping. Photoluminescence (PL) measurements showed that
sol–gel method. The X-ray diffraction (XRD) results showed the intensity of the ultraviolet (UV) emission band and the
the Zn0.985Cu0.02O and Zn0.95Fe0.03Cu0.02O samples were of visible-light emission band of Zn0.95Cu0.02Fe0.03O samples
single phase with the ZnO-like wurtzite structure. Magnetic increased and the UV emission peak exhibited blue shift
measurements indicated that room-temperature ferromagnet- compared to Zn0.98Cu0.02O samples.
ism of Zn0.98Cu0.02O was intrinsic in nature and the saturation
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1 Introduction ZnO-based diluted magnetic semi- solution. The mixture was then poured into citric acid
conductors (DMSs) have been predicted to exhibit ferro- [C6H8O7] (99.5%) while stirring. The solution was dried at
magnetic behavior with a Curie temperature (TC) above 80 oC to obtain a xerogel. After the swelled xerogel was
room temperature and to have a large saturation magnetiza- completed at 130 oC, a reticular substance was obtained,
tion (Ms), which makes them promising candidate materials which was then ground to powder in an agate mortar. The
for the next generation of spintronic devices with magnet- powder was sintered at 600 oC for 10 h under an air
ism controlled by electricity or optics [1–4]. Room- atmosphere. This method allows mixing of the chemicals
temperature ferromagnetism in ZnO-based DMSs have at the atomic level, thus reducing the possibility of
been reported by many groups [5–9]. Based on a number of undetectable impurity phase. Zn0.98ꢀxCu0.02FexO powders
experimental results, researchers found that the carrier were obtained after the sol–gel process and sintered. The
concentration in transition-metal-ion doped ZnO DMSs reaction mechanism of the decomposing citrate technique
could influence their properties. So, more groups have was described previously [14]. Zn0.98Cu0.02O power also
tried to dope other ions into the ZnO DMSs in order to obtained by the same procedure without the Fe (NO3)3ꢁ9H2O
change the magnetic and optical properties by introducing (99.9%) in the solution.
additional carriers [10–13]. In this work, we report the
Structural characterization of ZnO and Zn0.98ꢀx
room-temperature magnetic and optical properties of Cu0.02FexO (x ¼ 0, 0.03) was performed by X-ray diffraction
Zn0.98Cu0.02O and Zn0.95Cu0.02Fe0.03O powders prepared (XRD) on a D/max-2500 copper rotating-anode X-ray
by the sol–gel method. The effects of Fe on the structure, diffractometer with Cu Ka radiation (40 kV, 200 mA).
magnetic, and optical properties of Zn0.98Cu0.02O have been Magnetic hysteresis loops of Zn0.98Cu0.02O and Zn0.95
studied in detail.
Cu0.02Fe0.03O were measured by a Lake Shore 7407
vibrating sample magnetometer (VSM). The optical proper-
2 Experimental Appropriate proportions of Zn ties of samples were obtained by photoluminescence (PL)
(NO3)2ꢁ6H2O (99.9%), Cu (NO3)2ꢁ3H2O (99.9%), and Fe measurements using HR800 LabRam Infinity spectropho-
(NO3)3ꢁ9H2O (99.9%) high-purity powders were thoroughly tometer excited by a continuous He-Cd laser with a
mixed and dissolved into water to get a homogeneous wavelength of 325 nm at a power of 50 mW.
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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H. Liu et al.: Structure, magnetic, and optical properties in Zn0.98ꢀxCu0.02FexO diluted magnetic semiconductors
x=0.03
x=0
ZnO
30
40
50
60
70
2 (degree)
Figure 2 Magnetization versus field hysteresis (M–H) loops of
Zn0.98ꢀxCu0.02FexO (x ¼ 0, 0.03) at room temperature.
Figure 1 X-ray diffraction (XRD) patterns of ZnO and
Zn0.98ꢀxCu0.02FexO (x ¼ 0, 0.03) at room temperature.
3 Results and discussion Figure 1 shows the XRD metallic Fe. In the previous papers [15, 16], we reported that
patterns of ZnO and Zn0.98ꢀxCu0.02FexO (x ¼ 0, 0.03). The the origin of room temperature ferromagnetism in Cu- and
patterns show a hexagonal wurtzite structure that belongs to Fe-doped ZnO is the existence of the Cu and Fe element in
the C64v space group ðP63mcÞ according to the standard JCPDS the ZnO lattice and the Cu and Fe ion substitute into Zn sites.
card. No second phase, such as binary zinc–copper or zinc– Super- and double exchange give the explanation of our
iron phases, is detected within the sensitivity of XRD. In observed ferromagnetism. Several groups [17, 18] have
comparison with undoped ZnO, the XRD diffraction peaks found that the point defects play crucial roles in the FM of
of Zn0.98Cu0.02O are broadened due to the smaller size. ZnO-based DMSs. More detailed work is essential to
The mean grain size of the Zn0.98Cu0.02O is calculated to understand the magnetic behaviors of these materials.
be ꢂ38 nm by the Scherrer formula. However, the crystal
As we observed, the magnetization of Zn0.95Cu0.02Fe0.03
O
lattice has no obvious difference after Cu doping due to increases markedly in comparison with that of Zn0.98Cu0.02
O
the radius of Cu being similar to that of Zn. Compared powder samples. In other words, the introduction of Fe
with Zn0.98Cu0.02O, the XRD diffraction peaks of element can enhance the formation of ferromagnetic order.
Zn0.95Cu0.02Fe0.03O shifted to a larger angle. The shift of Mostresearchers[19–21]believed that Fedoped intoZnOacts
diffraction peaks may be associated with Fe doping. There as n-type dopant, while Cu in doped samples acts as a p-type
are three modes for the Fe doped into the ZnO lattice: Fe ions dopant, therefore, Fe and Cu play opposite roles in the ZnO
fill Zn vacancies of ZnO; Fe ions replaced the Zn2þ in ZnO as system. So, the working mechanism for our samples is n-type
replacement atoms, and Fe ions exist in the ZnO lattice as carrier-conditioneddouble-exchange.BecausetheFeindoped
interstitial atoms. Comparing the Zn ionic radius with that of ZnO is an n-type dopant, the effective electronic carrier
Fe ion with different valences, we believe that when Fe3þ concentration is increased after Fe doping, which finally
substitutes for Zn2þ, the bond length of the Fe–O in samples
0.8
is less than that of the original Zn–O, the lattice constant
Zn0.98Cu0.02
O
would become smaller and lead to the higher-angle shift of
the XRD diffraction peaks. Of course, the lattice constants of
ZnO will change during the annealing process under high
temperature, for our experimental setting the doping process
should be the main reason for the change of lattice constant.
Therefore, we speculate that Fe3þ ions replace the Zn2þ in
ZnO as replacement atoms in the samples. The mean grain
size of the Zn0.95Cu0.02Fe0.03O estimated was about 40 nm.
In order to study the effect of Fe on the magnetic
properties of Zn0.98Cu0.02O, the magnetization versus
magnetic field (M–H) curves of Zn0.985Cu0.02O and
Zn0.95Cu0.02Fe0.03O powders have been measured using a
VSM and the results are shown in Fig. 2. The two samples
exhibit ferromagnetic ordering at room temperature. The Ms
is 0.65 mB/Cu and 0.78 mB/Cu for Zn0.98Cu0.02O and
Zn0.95Fe0.03Cu0.02
O
0.6
0.4
0.2
0.0
300
350
T(K)
400
Figure 3 Magnetization versus temperature (M–T) loops of
Zn0.95Cu0.02Fe0.03O, which are much lower than that of Zn0.98ꢀxCu0.02FexO (x ¼ 0, 0.03) under 1 kOe.
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Original
Paper
Phys. Status Solidi A 207, No. 8 (2010)
1813
the Zn0.98Cu0.02O lattice, some new defects, such as oxygen
vacancies, Zn interstitials, and so on, are generated in
samples, which enhances the visible luminescence.
4 Conclusion In summary, we prepared Zn0.98
Cu0.02O and Zn0.95Cu0.02Fe0.03O powders by the sol-gel
method. Structure analyses indicate that both Cu-doped ZnO
and Cu, Fe codoped ZnO are wurtzite structure. The
magnetization results of Zn0.98Cu0.02
O
and Zn0.95
Cu0.02Fe0.03O powders show the room-temperature ferro-
magnetism of the samples in this study is an intrinsic
property. The Ms of Cu-dopedZnO increases after Fedoping.
The intensity of UV and visible-light emission in
Zn0.95Cu0.02Fe0.03O increase, and the UV emission peak
exhibits a blue shift compared to the Zn0.98Cu0.02O sample.
Acknowledgements This work was supported by the
financial support of the National Nature Science Foundation of
China (grant nos. 10804036,60778040; 60878039), National
Programs for High Technology Research and Development of
China(863) (item no. 2009AA03Z303), the Science and
Technology program of the ‘‘11th five-year’’ of Education for
Jilinprovince (no. 20070161), theScienceandTechnologyprogram
of Jilin province (no. 20080514), the Science and Technology
bureauofKeyProgramforMinistryofEducation(itemno.207025),
and the Program for the Development of Science and Technology of
Jilin province (item no. 20082112).
Figure 4 Photoluminescence (PL) spectra of Zn0.98ꢀxCu0.02FexO
(x ¼ 0, 0.03) at room temperature.
enhances ferromagnetic coupling in the system. Figure 3
shows the temperature dependence of magnetic moment
for Zn0.98ꢀxCu0.02FexO (x ¼ 0, 0.03) under 1 kOe. With
increased temperature, the magnetization moment for
Zn0.98ꢀxCu0.02FexO (x ¼ 0, 0.03) decreases and reaches the
TC below 335 and 345 K, respectively, which is below the TC
of iron oxide. Both of their TC are high enough for practical
applications at room temperature.
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