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Structural and magnetic properties of electrodeposited Ni nanowires
Journal of Alloys and Compounds 455 (2008) 17–20
Structural and magnetic properties of electrodeposited Ni nanowires Mousa M.A. Imran ∗ Materials Science Laboratory, Department of Basic Science, Prince Abdullah Bin Ghazi Faculty of Science and IT, Al-Balqa’ Applied University, Al-Salt 19117, Jordan Received 22 November 2006; received in revised form 8 January 2007; accepted 9 January 2007 Available online 18 January 2007
Abstract Ni nanowires of diameter 250 nm and 15 m length have been fabricated by electrodeposition, using two-electrode electrochemical cell, filling of highly ordered nanoporous alumina membrane. The formation of Ni nanowires has been ascertained by scanning electron microscope (SEM) and atomic force microscope (AFM) while the chemical composition has been analyzed with energy dispersive X-ray analysis (EDX). The structural characteristic of the wires was examined using X-ray diffraction showing (1 1 1) and (2 0 0) peaks of Ni. The magnetic state of individual nanowires was investigated by magnetic force microscope (MFM). The magnetic behavior of the array has been carried out at room temperature using a vibrating sample magnetometer (VSM). The obtained coercivity values of the wires were 47.2 and 27.3 kA/m when the applied field is perpendicular and parallel to the array surface, respectively. The remanence value, as evident from the hysteresis loops, is larger for the field applied along the wire axis. © 2007 Elsevier B.V. All rights reserved. Keywords: Ni nanowires; Electrodeposition; Alumina membrane; Coercivity
1. Introduction Attention has been devoted over the last decade to the physical behavior of the nanostructured materials due to their wide range of applications in high-density magnetic-recording media [1], single electron devices [2], biomedical application and various sensor devices [3]. Among these materials, metal nanowires have been the focus of extensive research activities due to their unusual properties [4]. Many researchers [5–7] have studied the magnetic properties of metal nanowires, but complete understanding of these properties is still waiting for intense investigation. Of particular interest is the behavior of closely spaced arrays of magnetic nanowires. In such arrays, the magnetic behavior of the individual elements and the interactions between elements determine the hysteresis behavior and hence determine its applicability for data storage. Although several methods [8–10] have been suggested for the preparation of nanowires, still electrodeposition technique is attractive not only because of its simplicity, but also because it has a number of unique features. The most important of which ∗
Tel.: +962 777 993459; fax: +962 5 3530462. E-mail address: [email protected].
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.01.051
is that this technique is cheap and reliable for producing large arrays of nanowires. In the present work, efforts have been made to fabricate Ni nanowires by electrodeposition method, in which Ni nanowires prepared into pores of the nanoporous anodic alumina. The formation of the nanowires has been ascertained using scanning electron microscope (SEM) and atomic force microscope (AFM), whereas the chemical composition has been ensured using energy dispersive X-ray (EDX). XRD analysis indicates the presence of (1 1 1) and (2 0 0) peaks of Ni. Besides to that, magnetic and structural behaviors have also been studied using vibrating sample magnetometer (VSM) and magnetic force microscope (MFM). 2. Experimental The porous alumina template (obtained from Whatman Company, England) was approximately 25 m in length and 250 nm in pore diameter. The template has pore densities as high as 1010 pores/cm2 . A very thin layer of GaIn eutectic was painted on one side of the membrane, to block the pores, and to serve as the cathode. The membrane is mounted on a copper plate, using an insulating electric tape. This avoids deposition of wires on the plate and allows the deposition of the nanowires on the GaIn (obtained from Aldrich, USA) layer from within the pore. Fig. 1 shows the electrodeposition cell, in which Ni wire is connected to work as an anode and Ni plating solution is added as an electrolyte. After several minutes,
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M.M.A. Imran / Journal of Alloys and Compounds 455 (2008) 17–20
Fig. 3. XRD pattern of Ni nanowires embedded inside porous of the alumina membrane. Fig. 1. Schematic diagram of sample preparation. depending on the desired length of the nanowires, the membrane is removed from the cell and the GaIn layer is removed by nitric acid. The membrane was kept in NaOH, to remove the polymer ring surrounding it, the alumina dissolved and the nanowires liberated, which are then suspended in water. The electrodeposition of the nanowires was taken for a period of 10, 15 and 30 min. The formation of Ni nanowires was confirmed using a SEM (JEOL, JSM 6100 model) equipped with EDX analysis (Oxford, 6779 model, England). A drop of Ni nanowire suspension has been allowed to dry on a smooth stainless steel disc (1.2 cm in diameter) to record the SEM and AFM images of the nanowires. AFM (Digital Instruments, USA) was used for the accurate determination of the length and diameter of the wires, meanwhile, MFM was used to image individual wires in the alumina template. The magnetic measurements were carried out at room temperature using a VSM.
3. Results and discussion Fig. 2 shows the SEM image of the nanowires that are deposited for 15 min. It is clear that most of the wires, which are cylindrical in shape as it is expected, are about 250 nm in diameter and coincide with the pore diameter but with an average length of 15 m and increases with the increase of deposition
Fig. 2. SEM image of Ni nanowires.
time. The XRD pattern of the Ni nanowires obtained into the anodic alumina membrane is shown in Fig. 3. The observed diffraction peaks correspond to the (1 1 1) and (2 0 0) of Ni and is an indication that Ni grows in its fcc crystal structure and is clearly polycrystalline. Meanwhile, the (2 2 0) peak seen in the spectrum is the aluminum reflection and this was also confirmed from the EDX analysis and agrees fairly well with the results reported by other workers [5]. Fig. 4 exhibits typical AFM (tapping mode) image of the Ni nanowires. The AFM of a bundle and a single nanowire are shown in Fig. 4(a) and (b), respectively. It is clear that the Ni nanowire is long and continuous, meanwhile the bundle is indication of incomplete dissolving. From the AFM images of the nanowires a small length distribution is observed. Therefore, for the sake of accuracy ten single nanowires have been taken to measure the length and diameter. It is found that Ni nanowires have diameters of 250 nm, but the length has an average value of 15 m. This irregular nanoporous distribution does not expect to alter the magnetic or the structural behavior of the nanowires. The MFM has been performed on Ni array in an attempt to image the state of individual particles, as shown in Fig. 5. From the MFM data, one deduces that the Ni pillars are single – domain nanomagnets aligned perpendicular to the surface. According to Nielsch et al. [11], the patterned domain structure is due to ferromagnetic alignment of pillars influenced by weak magnetic interaction between the nanomagnets. The observed black contrast is an indication that the magnetic moments of the wires are oriented out of plane in up and down direction and is in good agreement with the results reported in literature [12]. For further investigation of the magnetic behavior of the nanowire arrays, vibrating sample magnetometer was used to measure the room temperature hysteresis loop. The reduced hysteresis loop of the Ni nanowire arrays measured with the applied field either parallel or perpendicular to the surface of the array is given in Fig. 6. It is clear that the coercivity is greater when the field is perpendicular to the membrane surface than parallel to it, the coercivity is 47.2 and 27.3 kA/m, respectively. This suggest that the field required to reach the saturated magnetization, as shown in Fig. 6, is larger in the perpendicular case
M.M.A. Imran / Journal of Alloys and Compounds 455 (2008) 17–20
19
Fig. 6. Hysteresis loops of Ni nanowire arrays measured with the applied field perpendicular () and (—) parallel to the membrane surface.
and may be attributed to the shape anisotropy of the wires. This further means that the easy axis occurs along the long axis of the wires. This is the characteristic feature of polycrystalline materials [5], where the shape of anisotropy dominates over the intrinsic magnetocrystalline anisotropy, and hence dictates the magnetic behavior of the Ni nanowires. In the above discussion, it is mentioned that the MFM images of the wires are single domain. This is, however, possible if the reduced remenance M/Mo = 1 and all the wires giving the same magnetic contrast. In the present work, M/Mo = 0.74, see Fig. 6, and the shape of the loops slightly deviates from that the theory predicts. This deviation of the experimental data may be attributed to dipolar interactions. Indeed it is reported that [8,9] the low value of the reduced remanence is due to dipolar interactions because such interactions tend to shear the hysteresis loop in interacting systems especially in arrays of nanowires [13,14]. Fig. 4. (a) AFM image of a bundle of Ni nanowires. (b) AFM image of a single Ni nanowire.
4. Conclusions Ni nanowire has been prepared by electrodeposition method and their structural and magnetic properties have been carried out using different techniques. The structure of the wires is observed by AFM and is also characterized by EDX and XRD and is found to be polycrystalline. Investigation of the magnetic properties of the wires using MFM indicates that the moments of the wires oriented in up and down directions. The remenance value, obtained from the hysteresis loops using VSM, suggests that most of the sample’s magnetization is oriented along the wire axis when the field is removed. Acknowledgements
Fig. 5. Magnetic force microscope images, obtained at zero field, of Ni nanowires.
The author would like to thank Al-Balqa’ Applied University and Higher Education Development Project (Jordan) for the financial support provided during three months scientific visit to Washington State University. Thanks are also due to Prof. K.W. Hipps and Dr. Louis Scudiero, Material Science Program, Washington State University, Pullman, Washington, USA for preparation and characterization of the nanowires using their experimental setups.
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M.M.A. Imran / Journal of Alloys and Compounds 455 (2008) 17–20
References [1] R. O’Barr, S.Y. Yamamoto, S. Schultz, W. Xu, A. Scherer, J. Appl. Phys. 81 (1997) 4730. [2] A.A. Tager, J.M. Xu, M. Moskovits, Phys. Rev. B 33 (1997) 3715. [3] A. Fert, L. Piraux, J. Magn. Magn. Mater. 200 (2000) 338. [4] K.R. Pirota, D. Navas, M. Hernandez-Velez, K. Nielsch, M. Vazquez, J. Alloys Compd. 369 (2004) 18. [5] J. Qin, J. Nogues, M. Mikhaylova, A. Roig, J. Munoz, M. Muhammed, Chem. Mater. 17 (2005) 1829. [6] D.J. Sellmyer, M. Zheng, R. Skomski, Condens. Matter Phys. 13R (2001) 433. [7] H. Masuda, K. Fukuda, Science 268 (1995) 1466.
[8] J.I. Martin, J. Nogues, K. Liu, J. Vicent, I.K. Schuller, J. Magn. Magn. Mater. 256 (2003) 449. [9] R. Skomsky, J. Phys.: Condens. Matter 15 R (2003) 841. [10] C.A. Ross, Annu. Rev. Mater. Sci. 31 (2001) 203. [11] K. Nielsch, R.B. Wehrspohn, S.F. Fisher, H. Kronmuller, J. Barthel, J. Kirschner, U. Gosele, Mater. Res. Soc. Symp. Proc. 636. (2001). [12] C.A. Ross, M.H. wang, M. Shima, H.I. Smith, M. Farhoud, T.A. Savas, W. Schwarzacher, J. Parrochon, W. Escoffier, H. Neal Bertram, F.B. Humphrey, M. Redjdal, J. Magn. Magn. Mater. 249 (2002) 200. [13] V. Raposo, J.M. Garcia, J.M. Gonzalez, M. Vazquez, J. Magn. Magn. Mater. 222 (2000) 227. [14] C.A. Ross, M. Hwang, M. Shima, J.Y. Cheng, M. Farhoud, T.A. Savas, H.I. Smith, W. Schwarzacher, F.M. Ross, M. Redjdal, F.B. Humphrey, Phys. Rev. B 65 (2002) 144417.
Structural and magnetic properties of electrodeposited Ni nanowires Mousa M.A. Imran ∗ Materials Science Laboratory, Department of Basic Science, Prince Abdullah Bin Ghazi Faculty of Science and IT, Al-Balqa’ Applied University, Al-Salt 19117, Jordan Received 22 November 2006; received in revised form 8 January 2007; accepted 9 January 2007 Available online 18 January 2007
Abstract Ni nanowires of diameter 250 nm and 15 m length have been fabricated by electrodeposition, using two-electrode electrochemical cell, filling of highly ordered nanoporous alumina membrane. The formation of Ni nanowires has been ascertained by scanning electron microscope (SEM) and atomic force microscope (AFM) while the chemical composition has been analyzed with energy dispersive X-ray analysis (EDX). The structural characteristic of the wires was examined using X-ray diffraction showing (1 1 1) and (2 0 0) peaks of Ni. The magnetic state of individual nanowires was investigated by magnetic force microscope (MFM). The magnetic behavior of the array has been carried out at room temperature using a vibrating sample magnetometer (VSM). The obtained coercivity values of the wires were 47.2 and 27.3 kA/m when the applied field is perpendicular and parallel to the array surface, respectively. The remanence value, as evident from the hysteresis loops, is larger for the field applied along the wire axis. © 2007 Elsevier B.V. All rights reserved. Keywords: Ni nanowires; Electrodeposition; Alumina membrane; Coercivity
1. Introduction Attention has been devoted over the last decade to the physical behavior of the nanostructured materials due to their wide range of applications in high-density magnetic-recording media [1], single electron devices [2], biomedical application and various sensor devices [3]. Among these materials, metal nanowires have been the focus of extensive research activities due to their unusual properties [4]. Many researchers [5–7] have studied the magnetic properties of metal nanowires, but complete understanding of these properties is still waiting for intense investigation. Of particular interest is the behavior of closely spaced arrays of magnetic nanowires. In such arrays, the magnetic behavior of the individual elements and the interactions between elements determine the hysteresis behavior and hence determine its applicability for data storage. Although several methods [8–10] have been suggested for the preparation of nanowires, still electrodeposition technique is attractive not only because of its simplicity, but also because it has a number of unique features. The most important of which ∗
Tel.: +962 777 993459; fax: +962 5 3530462. E-mail address: [email protected].
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.01.051
is that this technique is cheap and reliable for producing large arrays of nanowires. In the present work, efforts have been made to fabricate Ni nanowires by electrodeposition method, in which Ni nanowires prepared into pores of the nanoporous anodic alumina. The formation of the nanowires has been ascertained using scanning electron microscope (SEM) and atomic force microscope (AFM), whereas the chemical composition has been ensured using energy dispersive X-ray (EDX). XRD analysis indicates the presence of (1 1 1) and (2 0 0) peaks of Ni. Besides to that, magnetic and structural behaviors have also been studied using vibrating sample magnetometer (VSM) and magnetic force microscope (MFM). 2. Experimental The porous alumina template (obtained from Whatman Company, England) was approximately 25 m in length and 250 nm in pore diameter. The template has pore densities as high as 1010 pores/cm2 . A very thin layer of GaIn eutectic was painted on one side of the membrane, to block the pores, and to serve as the cathode. The membrane is mounted on a copper plate, using an insulating electric tape. This avoids deposition of wires on the plate and allows the deposition of the nanowires on the GaIn (obtained from Aldrich, USA) layer from within the pore. Fig. 1 shows the electrodeposition cell, in which Ni wire is connected to work as an anode and Ni plating solution is added as an electrolyte. After several minutes,
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M.M.A. Imran / Journal of Alloys and Compounds 455 (2008) 17–20
Fig. 3. XRD pattern of Ni nanowires embedded inside porous of the alumina membrane. Fig. 1. Schematic diagram of sample preparation. depending on the desired length of the nanowires, the membrane is removed from the cell and the GaIn layer is removed by nitric acid. The membrane was kept in NaOH, to remove the polymer ring surrounding it, the alumina dissolved and the nanowires liberated, which are then suspended in water. The electrodeposition of the nanowires was taken for a period of 10, 15 and 30 min. The formation of Ni nanowires was confirmed using a SEM (JEOL, JSM 6100 model) equipped with EDX analysis (Oxford, 6779 model, England). A drop of Ni nanowire suspension has been allowed to dry on a smooth stainless steel disc (1.2 cm in diameter) to record the SEM and AFM images of the nanowires. AFM (Digital Instruments, USA) was used for the accurate determination of the length and diameter of the wires, meanwhile, MFM was used to image individual wires in the alumina template. The magnetic measurements were carried out at room temperature using a VSM.
3. Results and discussion Fig. 2 shows the SEM image of the nanowires that are deposited for 15 min. It is clear that most of the wires, which are cylindrical in shape as it is expected, are about 250 nm in diameter and coincide with the pore diameter but with an average length of 15 m and increases with the increase of deposition
Fig. 2. SEM image of Ni nanowires.
time. The XRD pattern of the Ni nanowires obtained into the anodic alumina membrane is shown in Fig. 3. The observed diffraction peaks correspond to the (1 1 1) and (2 0 0) of Ni and is an indication that Ni grows in its fcc crystal structure and is clearly polycrystalline. Meanwhile, the (2 2 0) peak seen in the spectrum is the aluminum reflection and this was also confirmed from the EDX analysis and agrees fairly well with the results reported by other workers [5]. Fig. 4 exhibits typical AFM (tapping mode) image of the Ni nanowires. The AFM of a bundle and a single nanowire are shown in Fig. 4(a) and (b), respectively. It is clear that the Ni nanowire is long and continuous, meanwhile the bundle is indication of incomplete dissolving. From the AFM images of the nanowires a small length distribution is observed. Therefore, for the sake of accuracy ten single nanowires have been taken to measure the length and diameter. It is found that Ni nanowires have diameters of 250 nm, but the length has an average value of 15 m. This irregular nanoporous distribution does not expect to alter the magnetic or the structural behavior of the nanowires. The MFM has been performed on Ni array in an attempt to image the state of individual particles, as shown in Fig. 5. From the MFM data, one deduces that the Ni pillars are single – domain nanomagnets aligned perpendicular to the surface. According to Nielsch et al. [11], the patterned domain structure is due to ferromagnetic alignment of pillars influenced by weak magnetic interaction between the nanomagnets. The observed black contrast is an indication that the magnetic moments of the wires are oriented out of plane in up and down direction and is in good agreement with the results reported in literature [12]. For further investigation of the magnetic behavior of the nanowire arrays, vibrating sample magnetometer was used to measure the room temperature hysteresis loop. The reduced hysteresis loop of the Ni nanowire arrays measured with the applied field either parallel or perpendicular to the surface of the array is given in Fig. 6. It is clear that the coercivity is greater when the field is perpendicular to the membrane surface than parallel to it, the coercivity is 47.2 and 27.3 kA/m, respectively. This suggest that the field required to reach the saturated magnetization, as shown in Fig. 6, is larger in the perpendicular case
M.M.A. Imran / Journal of Alloys and Compounds 455 (2008) 17–20
19
Fig. 6. Hysteresis loops of Ni nanowire arrays measured with the applied field perpendicular () and (—) parallel to the membrane surface.
and may be attributed to the shape anisotropy of the wires. This further means that the easy axis occurs along the long axis of the wires. This is the characteristic feature of polycrystalline materials [5], where the shape of anisotropy dominates over the intrinsic magnetocrystalline anisotropy, and hence dictates the magnetic behavior of the Ni nanowires. In the above discussion, it is mentioned that the MFM images of the wires are single domain. This is, however, possible if the reduced remenance M/Mo = 1 and all the wires giving the same magnetic contrast. In the present work, M/Mo = 0.74, see Fig. 6, and the shape of the loops slightly deviates from that the theory predicts. This deviation of the experimental data may be attributed to dipolar interactions. Indeed it is reported that [8,9] the low value of the reduced remanence is due to dipolar interactions because such interactions tend to shear the hysteresis loop in interacting systems especially in arrays of nanowires [13,14]. Fig. 4. (a) AFM image of a bundle of Ni nanowires. (b) AFM image of a single Ni nanowire.
4. Conclusions Ni nanowire has been prepared by electrodeposition method and their structural and magnetic properties have been carried out using different techniques. The structure of the wires is observed by AFM and is also characterized by EDX and XRD and is found to be polycrystalline. Investigation of the magnetic properties of the wires using MFM indicates that the moments of the wires oriented in up and down directions. The remenance value, obtained from the hysteresis loops using VSM, suggests that most of the sample’s magnetization is oriented along the wire axis when the field is removed. Acknowledgements
Fig. 5. Magnetic force microscope images, obtained at zero field, of Ni nanowires.
The author would like to thank Al-Balqa’ Applied University and Higher Education Development Project (Jordan) for the financial support provided during three months scientific visit to Washington State University. Thanks are also due to Prof. K.W. Hipps and Dr. Louis Scudiero, Material Science Program, Washington State University, Pullman, Washington, USA for preparation and characterization of the nanowires using their experimental setups.
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M.M.A. Imran / Journal of Alloys and Compounds 455 (2008) 17–20
References [1] R. O’Barr, S.Y. Yamamoto, S. Schultz, W. Xu, A. Scherer, J. Appl. Phys. 81 (1997) 4730. [2] A.A. Tager, J.M. Xu, M. Moskovits, Phys. Rev. B 33 (1997) 3715. [3] A. Fert, L. Piraux, J. Magn. Magn. Mater. 200 (2000) 338. [4] K.R. Pirota, D. Navas, M. Hernandez-Velez, K. Nielsch, M. Vazquez, J. Alloys Compd. 369 (2004) 18. [5] J. Qin, J. Nogues, M. Mikhaylova, A. Roig, J. Munoz, M. Muhammed, Chem. Mater. 17 (2005) 1829. [6] D.J. Sellmyer, M. Zheng, R. Skomski, Condens. Matter Phys. 13R (2001) 433. [7] H. Masuda, K. Fukuda, Science 268 (1995) 1466.
[8] J.I. Martin, J. Nogues, K. Liu, J. Vicent, I.K. Schuller, J. Magn. Magn. Mater. 256 (2003) 449. [9] R. Skomsky, J. Phys.: Condens. Matter 15 R (2003) 841. [10] C.A. Ross, Annu. Rev. Mater. Sci. 31 (2001) 203. [11] K. Nielsch, R.B. Wehrspohn, S.F. Fisher, H. Kronmuller, J. Barthel, J. Kirschner, U. Gosele, Mater. Res. Soc. Symp. Proc. 636. (2001). [12] C.A. Ross, M.H. wang, M. Shima, H.I. Smith, M. Farhoud, T.A. Savas, W. Schwarzacher, J. Parrochon, W. Escoffier, H. Neal Bertram, F.B. Humphrey, M. Redjdal, J. Magn. Magn. Mater. 249 (2002) 200. [13] V. Raposo, J.M. Garcia, J.M. Gonzalez, M. Vazquez, J. Magn. Magn. Mater. 222 (2000) 227. [14] C.A. Ross, M. Hwang, M. Shima, J.Y. Cheng, M. Farhoud, T.A. Savas, H.I. Smith, W. Schwarzacher, F.M. Ross, M. Redjdal, F.B. Humphrey, Phys. Rev. B 65 (2002) 144417.