- Email: [email protected]
CoO core–shell clusters
Materials Letters 188 (2017) 103–106
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Exchange bias of nanostructured films assembled with Co/CoO core–shell clusters QiaoXia Xing, Zhonglin Han, Shifeng Zhao
MARK
⁎
School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, PR China
A R T I C L E I N F O
A BS T RAC T
Keywords: Nanoparticles Magnetic materials Interfaces Nanocomposites
Nanostructured films assembled with Co/CoO core–shell clusters were prepared by low energy cluster beam deposition. The structure and magnetism of the films were investigated. It is shown that core–shell clusters are detected with the average diameter of 6.3 nm. And films assembled with clusters present exchange bias effect, which is attributed to the exchange interaction at the interface of Co and CoO layers. The present nanostructured films assembled with Co/CoO core–shell clusters promote its applications in ultrahigh-density magnetic recording, giant magnetoresistance, and spin-electronic devices.
1. Introduction
2. Experiment
The exchange bias effect, has been extensively studied due to its potential applications in permanent magnet materials and high density recording media [1]. It is observed in systems with ferromagnetic (FM)-antiferromagnetic (AFM) interfaces such as thin-film FM-AFM multilayers or FM nanoparticles coated by an AFM layer. This effect is characterized by a shift and broadening of the ferromagnetic hysteresis loop below the blocking temperature (TB), which are respectively attributed to the existence of pinned uncompensated spins as well as the enhanced coercive field due to the existence of rotatable uncompensated spins at the interface between AFM/FM. Generally, some inhomogeneous materials are also suggested as candidates for exchange bias effect, especially, Co/CoO core–shell systems typically show a high exchange bias field. And magnetic reversal mechanism, real roughness and spin structures at core–shell interface should be different from that of simple FM/AFM bilayers because of singledomain structure of Co core grains and the small size of cores and shell crystallites [2]. Many physical and chemical methods have been used to deposit metal and oxide thin films [8], however, it is a big challenge to prepare particles with a controlled and narrow size distribution and to study them in a reproducible way. Fortunately, a method was developed for the preparation of nanoparticles named low energy cluster beam deposition, by which some cluster-assembled metal, oxidation, alloy nanostructured films were obtained [3–6]. Therefore, this work aims to prepare cluster-assembled Co/CoO core–shell nanostructure by physical deposition method. The exchange bias effect was investigated in detail.
Schematic preparation setup and growth processing of the clusterassembled Co/CoO core–shell are shown in Fig. 1. A dc magnetronsputtering-gas-aggregation cluster source was used to produce the cluster beam. A stream of argon gas was injected through a ring structure close to the surface of a cobalt target. Another stream of oxygen was fed as a buffer gas through a gas inlet near the magnetron discharge head. A constant argon gas pressure of 70 Pa and oxygen gas pressure of 0.5 Pa were maintained in the sputtering chamber. Co clusters were formed and their outer spheres were oxidized. The clusters were carried by the gas stream out of the aggregation tube into vacuum through a nozzle since the gas pressure decreases gradually from the sputtering chamber to the deposition chamber. Then they continued to pass through a skimmer into a vacuum (~3×10−4 Pa) chamber and deposited on the Si substrate. During deposition, the clusters softly land onto the substrate with low energy. The energy of the atoms is quite low (below~10 meV/atom) according to the model in the previous work [3]. It is exactly a relatively low energy process compared with magnetron sputtering, atomic layer deposition or pulsed laser deposition [7–9]. Transmission electron microscopy (TEM) investigation of the samples was carried out with a FEI F20 electron microscope. Physical Property Measurement System was used to measure magnetic hysteresis loops (M-H) and temperature dependence of magnetization (M-T) curves. 3. Results and discussion TEM images of the oxide-coated Co clusters are shown in Fig. 1.
⁎
Corresponding author. E-mail address: [email protected] (S. Zhao).
http://dx.doi.org/10.1016/j.matlet.2016.11.057 Received 2 September 2016; Received in revised form 26 October 2016; Accepted 15 November 2016 Available online 16 November 2016 0167-577X/ © 2016 Elsevier B.V. All rights reserved.
Materials Letters 188 (2017) 103–106
Q. Xing et al.
Fig. 1. Schematic preparation setup and growth processing of the clusters.
where H1 and H2 are the left and right coercive fields, M1 and M2 are the above and below magnetization of hysteresis loops. Distinguishingly, the hysteresis loop shifts towards positive of the horizontal axis at 100 K, which is often called positive exchange bias. The magnitude of the cooling field needed to obtain a positive shift depends strongly on the microstructure and the interface coupling of the films. In the case of 100 K, something eventually dominates and polarizes the antiferromagnetic spins in an opposite direction to the other situations here. With the decrease of temperature, it exhibits vertical loop shifts and more common horizontal exchange bias, which suggests that the cluster-assembled films are not fully oxidized but maintains a core of metallic Co surrounded by CoO layer. Thus results are also certified by TEM studies. Thus the exchange bias effect above normally caused by unidirectional anisotropy can be qualitatively understood by assuming an exchange interaction at AFM-FM interface [10]. When a field is applied in the temperature range of neel temperature (TN) and curie temperature (TC), FM spins line up with the field, while the AFM spins remain random. When cooling to T < TN, owing to the interaction at the interface, the AFM spins next to FM align to those of FM. The other spin planes in AFM “follow” AFM order so as to produce zero net magnetization. As the field is reversed, FM spins start to rotate. However, for sufficiently large AFM anisotropy, AFM spins remain unchanged. Therefore, the interfacial interaction between FM-AFM spins tries to align FM spins with AFM spins at the interface. In other words, AFM spins at the interface exert a microscopic torque on FM spins to keep them in their original position. Hence, FM spins have one single stable configuration, i.e. the anisotropy is unidirectional. Thus, the field needed to reverse completely an FM layer will be larger if it is in contact with an AFM layer, because an extra field is needed to overcome the microscopic torque. Nevertheless, once the field is rotated back to its original direction, FM spins will start to rotate at a smaller field in virtue of the interaction with the
Individual nanoparticles nearly spherical with the average diameter of 6.3 nm and the particles sizes in the range of 6 ± 1 nm accounted for 78.2% of the total can be clearly distinguished. The darker regions in the core about 4 nm correspond to non-oxidized Co. The clusters have some seemingly amorphous regions on the shell about 2 nm, i.e. lower contrast areas, coexisting with the darker crystalline parts, corresponding to oxidized Co. Thus clusters with core–shell structure are formed. High resolution TEM (HRTEM) and selected area electron diffraction (SAED) further confirm thus core–shell nanostructure, as shown in Fig. 2. HRTEM and SAED pattern clearly shows a set of interplanar spacings at 0.202 nm that is indexed as the (002) reflection of the hcp Co lattice, the observed lattice fringe spacing of 0.151 nm is consistent with fcc CoO ((220) plane), the CoO lattice of (111), (222), (400), (420) and (422) are also observed in SAED, which simultaneously indicated the coexistence of fcc Co and CoO phases as revealed in Fig. 2(b) and (d). The magnetic hysteresis loops measured at different temperatures with the maximum external magnetic field of 1.5 T are shown in Fig. 3. It is shown that the hysteresis loops are symmetric with respect to the origin when the temperatures are higher than 200 K. However, as the temperatures are lower than 200 K, the exchange bias effect is obvious and the low temperature hysteresis loops in Fig. 3 demonstrate clockwise rotation. These loops systematically exhibit larger exchange bias field (HEB), coercivity (HC) and vertical shifts (MV) with the decrease of temperature. They are defined as
HEB =
H1 + H2 2
(1)
Hc =
H1 − H2 2
(2)
Mv =
M1 + M2 2
(3) 104
Materials Letters 188 (2017) 103–106
Q. Xing et al.
Fig. 2. (a) HRTEM image of monodispersed Co/CoO core–shell clusters deposited on a grid, (b) an expanded view on the particle encircled in image (a); (c) SAED pattern; (d) the corresponding analysis of SAED.
AFM spins. The material behaves as if there was an extra biasing field, which leads to FM hysteresis loop shift in the field axis, i.e. exchange bias. And, it is the combination of vertical and horizontal shifts that produces a “rotating” behavior with the increase of the temperature.
The temperature dependence of HEB, HC and MV is shown in Fig. 4. It is shown that the exchange bias effect becomes small and disappears at a special temperature called blocking temperature TB, which is related to the anisotropy of the antiferromagnetic materials. For the
Fig. 3. Hysteresis loops of nanostructured films assembled with Co/CoO core–shell clusters after zero-field cooling (ZFC) the sample at different temperature.
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Materials Letters 188 (2017) 103–106
Q. Xing et al.
change coupling between Co core and CoO shell. ZFC magnetization curves rapidly increase with the increase of temperature and reach a maximum at T=175 K. The sharp increase at 175 K is corresponding to the exchange bias onset temperature, above which the unidirectional exchange coupling between the Co and CoO phases vanishes, releasing the FM regions to reorient with the applied field. These behaviors indicate that unidirectional exchange anisotropy rapidly decreases above 175 K, which is consistent with the M-H results: the loop shift vanishes above a critical temperature of TB =175 K, correspondingly, FC and ZFC curves exhibit a rapid decline. 4. Conclusions In summary, the nanostructured films assembled with Co/CoO core–shell clusters exhibit exchange bias effect from hysteresis loops. The temperature dependence of magnetization reveals strong exchange coupling between the Co core and CoO shell when the temperature is blow 175 K. These effects are often ascribed to the formation of AFM domains which result in AFM pained and unpanied interfacial spins. During magnetization reversal, strongly pinned AFM spins give rise to the loop shift, whereas unpinned spins are mainly responsible for the enhancement of the coercivity.
Fig. 4. Temperature dependence of HC, HEB and Mv curves for Co/CoO core–shell clusters. Insert is ZFC and FC magnetization as a function of temperature for Co/CoO core–shell clusters at H=100 Oe.
present nanostructured films, the corresponding TB=175 K. HEB almost linearly decreases with the increasing of temperature up to TB and then becomes zero above TB. This behavior is attributed to the decrease of antiferromagnetic anisotropy because the antiferromagnetic interactions become more and more weaker with the increase of the temperature. In addition, the tendency for the change of vertical shift is same as that of exchange bias, which verifies the same origin of vertical and horizontal shift. Besides, HC increases with temperature decrease below TB. In the case of an AFM layer with relatively small anisotropy, when FM rotates, it “drags” AFM unpinned spins irreversibly, hence increasing FM coercivity. In a word, this indicates the increase in the effective magnetic anisotropy of the layer and the interfacial exchange coupling between Co and CoO layer with the decrease of the temperature below TB. Yet, for a relatively large AFM anisotropy, FM decouples because it cannot drag many unpinned AFM spins, consequently the coercivity is reduced. As the anisotropy decreases, FM is able to drag increasingly more AFM spins, thus the coercivity increases. Above TB AFM is random, thus it does not hinder FM rotation. Therefore, the anisotropy and coercivity exhibits a peak at TB. Insert of Fig. 4 depicts field cooling (FC) and zero field cooling (ZFC) magnetization curves measured from an as-deposited film. It is shown that the change tendency of FC magnetization is consists with that of the saturation magnetization obtained in hysteresis loops. And FC magnetization unchanged below 150 K confirms the strong ex-
Acknowledgments This work was financially supported by National Natural Science Foundation of China (Grant nos. 11264026, 11564028), and Inner Mongolia Science Foundation for Distinguished Young Scholars (Grant no. 2014JQ01). References [1] D.X. Zheng, J.L. Gong, C. Jin, P. Li, H.L. Bai, Mater. Lett. 156 (2015) 125. [2] D.L. Peng, T. Hihara, S. Yamamuro, T.J. Konno, Phys. Rev. B 61 (2000) 3103. [3] S.F. Zhao, M.L. Yao, J.G. Wan, Y.W. Mu, J.F. Zhou, G.H. Wang, Eur. Phys. J. D. 52 (2009) 163. [4] S.F. Zhao, C.H. Yao, Q. Lu, F.Q. Song, J.G. Wan, G.H. Wang, Trans. Nonferrous Met. Soc. China 6 (2009) 1450. [5] S.F. Zhao, F. Bi, J.G. Wan, M. Han, F.Q. Song, J.M. Liu, G.H. Wang, Nanotechnology 18 (2007) 265705. [6] S.F. Zhao, Z. Ma, W.Y. Xing, Y.N.N. Ma, A. Bai, Q. Yun, Thin Solid Films 570 (2014) 351. [7] K. Ahadi, K. Cadien, RSC Adv. 6 (2016) 16301. [8] K. Ahadi, A. Nemati, S.M. Mahdavi, Mater. Lett. 83 (2012) 124. [9] K. Ahadi, A. Nemati, S.M. Mahdavi, A. Vaezi, J. Mater. Sci.: Mater. Electron 24 (2013) 2128. [10] Z.W. Jiao, H.J. Chen, W.D. Jiang, J.F. Wang, D. Cao, Y. Zhou, et al., Mater. Lett. 168 (2016) 200.
106
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Exchange bias of nanostructured films assembled with Co/CoO core–shell clusters QiaoXia Xing, Zhonglin Han, Shifeng Zhao
MARK
⁎
School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, PR China
A R T I C L E I N F O
A BS T RAC T
Keywords: Nanoparticles Magnetic materials Interfaces Nanocomposites
Nanostructured films assembled with Co/CoO core–shell clusters were prepared by low energy cluster beam deposition. The structure and magnetism of the films were investigated. It is shown that core–shell clusters are detected with the average diameter of 6.3 nm. And films assembled with clusters present exchange bias effect, which is attributed to the exchange interaction at the interface of Co and CoO layers. The present nanostructured films assembled with Co/CoO core–shell clusters promote its applications in ultrahigh-density magnetic recording, giant magnetoresistance, and spin-electronic devices.
1. Introduction
2. Experiment
The exchange bias effect, has been extensively studied due to its potential applications in permanent magnet materials and high density recording media [1]. It is observed in systems with ferromagnetic (FM)-antiferromagnetic (AFM) interfaces such as thin-film FM-AFM multilayers or FM nanoparticles coated by an AFM layer. This effect is characterized by a shift and broadening of the ferromagnetic hysteresis loop below the blocking temperature (TB), which are respectively attributed to the existence of pinned uncompensated spins as well as the enhanced coercive field due to the existence of rotatable uncompensated spins at the interface between AFM/FM. Generally, some inhomogeneous materials are also suggested as candidates for exchange bias effect, especially, Co/CoO core–shell systems typically show a high exchange bias field. And magnetic reversal mechanism, real roughness and spin structures at core–shell interface should be different from that of simple FM/AFM bilayers because of singledomain structure of Co core grains and the small size of cores and shell crystallites [2]. Many physical and chemical methods have been used to deposit metal and oxide thin films [8], however, it is a big challenge to prepare particles with a controlled and narrow size distribution and to study them in a reproducible way. Fortunately, a method was developed for the preparation of nanoparticles named low energy cluster beam deposition, by which some cluster-assembled metal, oxidation, alloy nanostructured films were obtained [3–6]. Therefore, this work aims to prepare cluster-assembled Co/CoO core–shell nanostructure by physical deposition method. The exchange bias effect was investigated in detail.
Schematic preparation setup and growth processing of the clusterassembled Co/CoO core–shell are shown in Fig. 1. A dc magnetronsputtering-gas-aggregation cluster source was used to produce the cluster beam. A stream of argon gas was injected through a ring structure close to the surface of a cobalt target. Another stream of oxygen was fed as a buffer gas through a gas inlet near the magnetron discharge head. A constant argon gas pressure of 70 Pa and oxygen gas pressure of 0.5 Pa were maintained in the sputtering chamber. Co clusters were formed and their outer spheres were oxidized. The clusters were carried by the gas stream out of the aggregation tube into vacuum through a nozzle since the gas pressure decreases gradually from the sputtering chamber to the deposition chamber. Then they continued to pass through a skimmer into a vacuum (~3×10−4 Pa) chamber and deposited on the Si substrate. During deposition, the clusters softly land onto the substrate with low energy. The energy of the atoms is quite low (below~10 meV/atom) according to the model in the previous work [3]. It is exactly a relatively low energy process compared with magnetron sputtering, atomic layer deposition or pulsed laser deposition [7–9]. Transmission electron microscopy (TEM) investigation of the samples was carried out with a FEI F20 electron microscope. Physical Property Measurement System was used to measure magnetic hysteresis loops (M-H) and temperature dependence of magnetization (M-T) curves. 3. Results and discussion TEM images of the oxide-coated Co clusters are shown in Fig. 1.
⁎
Corresponding author. E-mail address: [email protected] (S. Zhao).
http://dx.doi.org/10.1016/j.matlet.2016.11.057 Received 2 September 2016; Received in revised form 26 October 2016; Accepted 15 November 2016 Available online 16 November 2016 0167-577X/ © 2016 Elsevier B.V. All rights reserved.
Materials Letters 188 (2017) 103–106
Q. Xing et al.
Fig. 1. Schematic preparation setup and growth processing of the clusters.
where H1 and H2 are the left and right coercive fields, M1 and M2 are the above and below magnetization of hysteresis loops. Distinguishingly, the hysteresis loop shifts towards positive of the horizontal axis at 100 K, which is often called positive exchange bias. The magnitude of the cooling field needed to obtain a positive shift depends strongly on the microstructure and the interface coupling of the films. In the case of 100 K, something eventually dominates and polarizes the antiferromagnetic spins in an opposite direction to the other situations here. With the decrease of temperature, it exhibits vertical loop shifts and more common horizontal exchange bias, which suggests that the cluster-assembled films are not fully oxidized but maintains a core of metallic Co surrounded by CoO layer. Thus results are also certified by TEM studies. Thus the exchange bias effect above normally caused by unidirectional anisotropy can be qualitatively understood by assuming an exchange interaction at AFM-FM interface [10]. When a field is applied in the temperature range of neel temperature (TN) and curie temperature (TC), FM spins line up with the field, while the AFM spins remain random. When cooling to T < TN, owing to the interaction at the interface, the AFM spins next to FM align to those of FM. The other spin planes in AFM “follow” AFM order so as to produce zero net magnetization. As the field is reversed, FM spins start to rotate. However, for sufficiently large AFM anisotropy, AFM spins remain unchanged. Therefore, the interfacial interaction between FM-AFM spins tries to align FM spins with AFM spins at the interface. In other words, AFM spins at the interface exert a microscopic torque on FM spins to keep them in their original position. Hence, FM spins have one single stable configuration, i.e. the anisotropy is unidirectional. Thus, the field needed to reverse completely an FM layer will be larger if it is in contact with an AFM layer, because an extra field is needed to overcome the microscopic torque. Nevertheless, once the field is rotated back to its original direction, FM spins will start to rotate at a smaller field in virtue of the interaction with the
Individual nanoparticles nearly spherical with the average diameter of 6.3 nm and the particles sizes in the range of 6 ± 1 nm accounted for 78.2% of the total can be clearly distinguished. The darker regions in the core about 4 nm correspond to non-oxidized Co. The clusters have some seemingly amorphous regions on the shell about 2 nm, i.e. lower contrast areas, coexisting with the darker crystalline parts, corresponding to oxidized Co. Thus clusters with core–shell structure are formed. High resolution TEM (HRTEM) and selected area electron diffraction (SAED) further confirm thus core–shell nanostructure, as shown in Fig. 2. HRTEM and SAED pattern clearly shows a set of interplanar spacings at 0.202 nm that is indexed as the (002) reflection of the hcp Co lattice, the observed lattice fringe spacing of 0.151 nm is consistent with fcc CoO ((220) plane), the CoO lattice of (111), (222), (400), (420) and (422) are also observed in SAED, which simultaneously indicated the coexistence of fcc Co and CoO phases as revealed in Fig. 2(b) and (d). The magnetic hysteresis loops measured at different temperatures with the maximum external magnetic field of 1.5 T are shown in Fig. 3. It is shown that the hysteresis loops are symmetric with respect to the origin when the temperatures are higher than 200 K. However, as the temperatures are lower than 200 K, the exchange bias effect is obvious and the low temperature hysteresis loops in Fig. 3 demonstrate clockwise rotation. These loops systematically exhibit larger exchange bias field (HEB), coercivity (HC) and vertical shifts (MV) with the decrease of temperature. They are defined as
HEB =
H1 + H2 2
(1)
Hc =
H1 − H2 2
(2)
Mv =
M1 + M2 2
(3) 104
Materials Letters 188 (2017) 103–106
Q. Xing et al.
Fig. 2. (a) HRTEM image of monodispersed Co/CoO core–shell clusters deposited on a grid, (b) an expanded view on the particle encircled in image (a); (c) SAED pattern; (d) the corresponding analysis of SAED.
AFM spins. The material behaves as if there was an extra biasing field, which leads to FM hysteresis loop shift in the field axis, i.e. exchange bias. And, it is the combination of vertical and horizontal shifts that produces a “rotating” behavior with the increase of the temperature.
The temperature dependence of HEB, HC and MV is shown in Fig. 4. It is shown that the exchange bias effect becomes small and disappears at a special temperature called blocking temperature TB, which is related to the anisotropy of the antiferromagnetic materials. For the
Fig. 3. Hysteresis loops of nanostructured films assembled with Co/CoO core–shell clusters after zero-field cooling (ZFC) the sample at different temperature.
105
Materials Letters 188 (2017) 103–106
Q. Xing et al.
change coupling between Co core and CoO shell. ZFC magnetization curves rapidly increase with the increase of temperature and reach a maximum at T=175 K. The sharp increase at 175 K is corresponding to the exchange bias onset temperature, above which the unidirectional exchange coupling between the Co and CoO phases vanishes, releasing the FM regions to reorient with the applied field. These behaviors indicate that unidirectional exchange anisotropy rapidly decreases above 175 K, which is consistent with the M-H results: the loop shift vanishes above a critical temperature of TB =175 K, correspondingly, FC and ZFC curves exhibit a rapid decline. 4. Conclusions In summary, the nanostructured films assembled with Co/CoO core–shell clusters exhibit exchange bias effect from hysteresis loops. The temperature dependence of magnetization reveals strong exchange coupling between the Co core and CoO shell when the temperature is blow 175 K. These effects are often ascribed to the formation of AFM domains which result in AFM pained and unpanied interfacial spins. During magnetization reversal, strongly pinned AFM spins give rise to the loop shift, whereas unpinned spins are mainly responsible for the enhancement of the coercivity.
Fig. 4. Temperature dependence of HC, HEB and Mv curves for Co/CoO core–shell clusters. Insert is ZFC and FC magnetization as a function of temperature for Co/CoO core–shell clusters at H=100 Oe.
present nanostructured films, the corresponding TB=175 K. HEB almost linearly decreases with the increasing of temperature up to TB and then becomes zero above TB. This behavior is attributed to the decrease of antiferromagnetic anisotropy because the antiferromagnetic interactions become more and more weaker with the increase of the temperature. In addition, the tendency for the change of vertical shift is same as that of exchange bias, which verifies the same origin of vertical and horizontal shift. Besides, HC increases with temperature decrease below TB. In the case of an AFM layer with relatively small anisotropy, when FM rotates, it “drags” AFM unpinned spins irreversibly, hence increasing FM coercivity. In a word, this indicates the increase in the effective magnetic anisotropy of the layer and the interfacial exchange coupling between Co and CoO layer with the decrease of the temperature below TB. Yet, for a relatively large AFM anisotropy, FM decouples because it cannot drag many unpinned AFM spins, consequently the coercivity is reduced. As the anisotropy decreases, FM is able to drag increasingly more AFM spins, thus the coercivity increases. Above TB AFM is random, thus it does not hinder FM rotation. Therefore, the anisotropy and coercivity exhibits a peak at TB. Insert of Fig. 4 depicts field cooling (FC) and zero field cooling (ZFC) magnetization curves measured from an as-deposited film. It is shown that the change tendency of FC magnetization is consists with that of the saturation magnetization obtained in hysteresis loops. And FC magnetization unchanged below 150 K confirms the strong ex-
Acknowledgments This work was financially supported by National Natural Science Foundation of China (Grant nos. 11264026, 11564028), and Inner Mongolia Science Foundation for Distinguished Young Scholars (Grant no. 2014JQ01). References [1] D.X. Zheng, J.L. Gong, C. Jin, P. Li, H.L. Bai, Mater. Lett. 156 (2015) 125. [2] D.L. Peng, T. Hihara, S. Yamamuro, T.J. Konno, Phys. Rev. B 61 (2000) 3103. [3] S.F. Zhao, M.L. Yao, J.G. Wan, Y.W. Mu, J.F. Zhou, G.H. Wang, Eur. Phys. J. D. 52 (2009) 163. [4] S.F. Zhao, C.H. Yao, Q. Lu, F.Q. Song, J.G. Wan, G.H. Wang, Trans. Nonferrous Met. Soc. China 6 (2009) 1450. [5] S.F. Zhao, F. Bi, J.G. Wan, M. Han, F.Q. Song, J.M. Liu, G.H. Wang, Nanotechnology 18 (2007) 265705. [6] S.F. Zhao, Z. Ma, W.Y. Xing, Y.N.N. Ma, A. Bai, Q. Yun, Thin Solid Films 570 (2014) 351. [7] K. Ahadi, K. Cadien, RSC Adv. 6 (2016) 16301. [8] K. Ahadi, A. Nemati, S.M. Mahdavi, Mater. Lett. 83 (2012) 124. [9] K. Ahadi, A. Nemati, S.M. Mahdavi, A. Vaezi, J. Mater. Sci.: Mater. Electron 24 (2013) 2128. [10] Z.W. Jiao, H.J. Chen, W.D. Jiang, J.F. Wang, D. Cao, Y. Zhou, et al., Mater. Lett. 168 (2016) 200.
106