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Cu electrodeposited multilayers
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
Structural, magnetic and transport properties of CoZn/Cu electrodeposited multilayers T. El Bahraouia, H. Errahmania, A. Berradaa,*, A. Diniab, G. Schmerberb, F. Cherkaoui El Mourslic, F. Hajjic, H. Lassrid a
Laboratoire de Physique des Mat!eriaux, Facult!e des Sciences, BP 1014 Rabat, Morocco b IPCMS-GEMM, ULP, UMR 46 CNRS, 23 rue du loess, 67037 Strasbourg, France c LECA, D!epartement de Chimie, Facult!e des Sciences, BP 1014 Rabat, Morocco d L.P.M., D!epartement de Physique, Facult!e des Sciences, Ain Chock, BP 5356 Casablanca, Morocco
Abstract We present experimental results of (Co9.7Zn90.3/Cu)20 multilayers grown from electrochemical dual bath. X-ray diffraction patterns have shown that the CoZn structural lattice parameters are close to those of the monoclinic CoZn13 compound. The magnetic properties at room temperature reveal both superparamagnetic and ferromagnetic features. The magnetoresistance behaviour exhibits a broad, rounded maximum around H=0 and does not present any saturation. r 2003 Published by Elsevier B.V. PACS: 75.30.Et; 75.50.Cc; 75.70.Cn Keywords: CoZn/Cu; Multilayers; Electrodeposition; Magnetoresistance; Superparamagnetism
Electrochemical deposition technique for multilayer in which the magnetic layer is a binary alloy has not been extensively used even if certain properties offered by this technique can be comparable to those of others techniques [1]. It has been previously shown that the magnetoresistance of electrodeposited Co/Cu multilayers is comparable to the sputtered and MBE grown Co/Cu samples and a small antiferromagnetic coupling between magnetic layers give rise to a relatively high magnetoresistance [2]. The aim of this work was to produce electrodeposited (CoxZn1x/Cu)n multilayers not studied until now and to investigate the structural, the magnetic and the transport properties. The (CoxZn1x/Cu) multilayers have been grown using the electrodeposition technique by the dual bath. The magnetic CoxZn1x layer was deposited in the electrolyte bath containing CoCl2 6H2O; CoSO4 7H2O; ZnSO4 7H2O; (NH4)2SO4 and H3BO3. *Corresponding author. Tel./fax: +212-37-67-11-18. E-mail address: [email protected] (A. Berrada). 0304-8853/$ - see front matter r 2003 Published by Elsevier B.V. doi:10.1016/j.jmmm.2003.12.266
The Cu layer was deposited during t=2 s for a current density of about 20 mA/cm2 in the electrolyte bath, which contains CuSO4 5H2O and H2SO4. The thickness of the CoZn alloy was fixed at 12 nm, whereas the Cu layer thickness was tCu=3 nm. The samples have been deposited on glass (or SiO2) substrates, covered by a 240 nm thick Cu buffer layer sputter-deposited at room temperature. SEM observations have shown homogenous surface morphology. The atomic percentages of the deposited elements were determined by the energy dispersive X-ray analysis (EDAX). Several techniques as high angle X-ray diffraction, alternating gradient force magnetometer (AGFM) and four-terminal magnetoresistivity measurements have been used to characterize these samples. Figs. 1a and b show X-ray, y22y; spectra recorded using CoK!a1 radiation (l=0.1789 nm) of the (Co9.7Zn90.3/Cu)20 and (Co4.6Zn95.4/Cu)10 multilayers. In addition to the strong (1 1 1) and (2 0 0) Cu buffer diffraction peaks, we observe a large number of Bragg peaks that correspond to the polycrystalline monoclinic CoZn13 phase. The presence of the first order satellites
ARTICLE IN PRESS T. El Bahraoui et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
e956
0.30
Cu (111)
(Co9.7Zn90.3/ Cu)20
[Co9.7Zn90.3/Cu]20
CoZn13 (331)
CoZn13 (400) CoZn13 (220)
T=300K 0.20
CoZn13 (402)
Cu (200) Cu (220)
CoZn13 (244)
MR%
Intensity (u. a.)
0.25
0.15
0.10
0.05
20
30
40
(a)
50
60
70
80
90 0.00
Angle 2Θ (degree)
-15
-10
-5
0
5
10
15
Magnetic field H(kOe) Multilayer
[Co
4.6
Cu (111)
Zn
95.4
/ Cu]
Fig. 3. Magnetoresistance loop for the (Co9.7Zn90.3/Cu)20 multilayer with the magnetic field in the film plane.
10
Intensity (u. a.)
Substrat
CoZn13 (402) satellites
20
30
40
50
60
70
80
90
Angle (2Θ) (degree)
(b)
Fig. 1. (a–b) y22y spectra recorded for the (Co4.6Zn95.4/Cu)20 and (Co9.7Zn90.3/Cu)20 multilayers. The insert shows the multilayer peak (SRn ) and the first order satellites SRn1 and SRnþ1 :
1.0 M/ M0 (13kOe)
(Co9.7Zn90.3/ Cu)20
0.5
T=300K
0.0
-0.5
-1.0 -15
-10
5
0 5 10 Magnetic field H(kOe)
15
Fig. 2. Magnetization loop for the (Co9.7Zn90.3/Cu)20 multilayer with the magnetic field in the film plane.
(Fig. 1b), labelled SRn1 and SRnþ1 indicates the good samples quality. Detailed structural and magnetic analysis has been performed with varying the Co concentration and will be published elsewhere.
Fig. 2 shows the magnetization hysteresis loop of the (Co9.7Zn90.3/Cu)20 multilayer. It is clearly shown that the saturation is not reached even for applied magnetic field as high as 14 kOe. This indicates that the magnetization results from ferromagnetic contribution at small fields and superparamagnetic contribution at high fields. This is further confirmed by the magnetoresistance (MR) curve reported in Fig. 3. The MR(H) loop displays a broad, rounded maximum around H ¼ 0 and does not present saturation even for applied fields as high as 17 kOe. We note also that the MR ratio obtained for this sample is relatively small compared to the Co/Cu electrodeposited multilayers [2]. The small MR value can be explained by several effects: (i) a shunting effect due to the thick Cu buffer layer (ii) the existence of mixed region at the interfaces with a formation of a ternary CoZnCu phase. Such ternary CoZrCu alloy at the interfaces was already observed in sputtered CoZr/Cu/Co sandwiches [3]. We have shown that is possible to grow welldefined electrodeposited multilayers consisting of ferromagnetic CoxZn1x alloys separated by nonmagnetic Cu layer. With the interfacial effects we have explained the superparamagnetic magnetization behaviour and the fall of the magnetoresistance as compared to Co/Cu prepared by the same technique. This work has been supported by the PICS (Programme International de Coop!eration Scientifique) contracted between CNRST (Morocco) and IPCMSCNRS (France).
ARTICLE IN PRESS T. El Bahraoui et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
References [1] R.D.M. Michael, V. Atzmony, C. Beauchamp, L.H. Benne Swartzendruber, D.S. Lashmore, L.T. Romankiw, J. Magn. Magn. Mater. 113 (1992) 149. [2] H. El Fanity, K. Rahmouni, M. Bouanani, A. Dinia, G. Schmerber, C. M!eny, P. Panissod, A. Cziraki,
e957
F. Cherkaoui, A. Berrada, Thin Solid Films 318 (1998) 227. [3] M. El Harfaoui, M. Faris, A. Qachaou, J. Ben Youssef, H. Le Gall, D. Meziane Mtalsi, J. Magn. Magn. Mater. 223 (2001) 81.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
Structural, magnetic and transport properties of CoZn/Cu electrodeposited multilayers T. El Bahraouia, H. Errahmania, A. Berradaa,*, A. Diniab, G. Schmerberb, F. Cherkaoui El Mourslic, F. Hajjic, H. Lassrid a
Laboratoire de Physique des Mat!eriaux, Facult!e des Sciences, BP 1014 Rabat, Morocco b IPCMS-GEMM, ULP, UMR 46 CNRS, 23 rue du loess, 67037 Strasbourg, France c LECA, D!epartement de Chimie, Facult!e des Sciences, BP 1014 Rabat, Morocco d L.P.M., D!epartement de Physique, Facult!e des Sciences, Ain Chock, BP 5356 Casablanca, Morocco
Abstract We present experimental results of (Co9.7Zn90.3/Cu)20 multilayers grown from electrochemical dual bath. X-ray diffraction patterns have shown that the CoZn structural lattice parameters are close to those of the monoclinic CoZn13 compound. The magnetic properties at room temperature reveal both superparamagnetic and ferromagnetic features. The magnetoresistance behaviour exhibits a broad, rounded maximum around H=0 and does not present any saturation. r 2003 Published by Elsevier B.V. PACS: 75.30.Et; 75.50.Cc; 75.70.Cn Keywords: CoZn/Cu; Multilayers; Electrodeposition; Magnetoresistance; Superparamagnetism
Electrochemical deposition technique for multilayer in which the magnetic layer is a binary alloy has not been extensively used even if certain properties offered by this technique can be comparable to those of others techniques [1]. It has been previously shown that the magnetoresistance of electrodeposited Co/Cu multilayers is comparable to the sputtered and MBE grown Co/Cu samples and a small antiferromagnetic coupling between magnetic layers give rise to a relatively high magnetoresistance [2]. The aim of this work was to produce electrodeposited (CoxZn1x/Cu)n multilayers not studied until now and to investigate the structural, the magnetic and the transport properties. The (CoxZn1x/Cu) multilayers have been grown using the electrodeposition technique by the dual bath. The magnetic CoxZn1x layer was deposited in the electrolyte bath containing CoCl2 6H2O; CoSO4 7H2O; ZnSO4 7H2O; (NH4)2SO4 and H3BO3. *Corresponding author. Tel./fax: +212-37-67-11-18. E-mail address: [email protected] (A. Berrada). 0304-8853/$ - see front matter r 2003 Published by Elsevier B.V. doi:10.1016/j.jmmm.2003.12.266
The Cu layer was deposited during t=2 s for a current density of about 20 mA/cm2 in the electrolyte bath, which contains CuSO4 5H2O and H2SO4. The thickness of the CoZn alloy was fixed at 12 nm, whereas the Cu layer thickness was tCu=3 nm. The samples have been deposited on glass (or SiO2) substrates, covered by a 240 nm thick Cu buffer layer sputter-deposited at room temperature. SEM observations have shown homogenous surface morphology. The atomic percentages of the deposited elements were determined by the energy dispersive X-ray analysis (EDAX). Several techniques as high angle X-ray diffraction, alternating gradient force magnetometer (AGFM) and four-terminal magnetoresistivity measurements have been used to characterize these samples. Figs. 1a and b show X-ray, y22y; spectra recorded using CoK!a1 radiation (l=0.1789 nm) of the (Co9.7Zn90.3/Cu)20 and (Co4.6Zn95.4/Cu)10 multilayers. In addition to the strong (1 1 1) and (2 0 0) Cu buffer diffraction peaks, we observe a large number of Bragg peaks that correspond to the polycrystalline monoclinic CoZn13 phase. The presence of the first order satellites
ARTICLE IN PRESS T. El Bahraoui et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
e956
0.30
Cu (111)
(Co9.7Zn90.3/ Cu)20
[Co9.7Zn90.3/Cu]20
CoZn13 (331)
CoZn13 (400) CoZn13 (220)
T=300K 0.20
CoZn13 (402)
Cu (200) Cu (220)
CoZn13 (244)
MR%
Intensity (u. a.)
0.25
0.15
0.10
0.05
20
30
40
(a)
50
60
70
80
90 0.00
Angle 2Θ (degree)
-15
-10
-5
0
5
10
15
Magnetic field H(kOe) Multilayer
[Co
4.6
Cu (111)
Zn
95.4
/ Cu]
Fig. 3. Magnetoresistance loop for the (Co9.7Zn90.3/Cu)20 multilayer with the magnetic field in the film plane.
10
Intensity (u. a.)
Substrat
CoZn13 (402) satellites
20
30
40
50
60
70
80
90
Angle (2Θ) (degree)
(b)
Fig. 1. (a–b) y22y spectra recorded for the (Co4.6Zn95.4/Cu)20 and (Co9.7Zn90.3/Cu)20 multilayers. The insert shows the multilayer peak (SRn ) and the first order satellites SRn1 and SRnþ1 :
1.0 M/ M0 (13kOe)
(Co9.7Zn90.3/ Cu)20
0.5
T=300K
0.0
-0.5
-1.0 -15
-10
5
0 5 10 Magnetic field H(kOe)
15
Fig. 2. Magnetization loop for the (Co9.7Zn90.3/Cu)20 multilayer with the magnetic field in the film plane.
(Fig. 1b), labelled SRn1 and SRnþ1 indicates the good samples quality. Detailed structural and magnetic analysis has been performed with varying the Co concentration and will be published elsewhere.
Fig. 2 shows the magnetization hysteresis loop of the (Co9.7Zn90.3/Cu)20 multilayer. It is clearly shown that the saturation is not reached even for applied magnetic field as high as 14 kOe. This indicates that the magnetization results from ferromagnetic contribution at small fields and superparamagnetic contribution at high fields. This is further confirmed by the magnetoresistance (MR) curve reported in Fig. 3. The MR(H) loop displays a broad, rounded maximum around H ¼ 0 and does not present saturation even for applied fields as high as 17 kOe. We note also that the MR ratio obtained for this sample is relatively small compared to the Co/Cu electrodeposited multilayers [2]. The small MR value can be explained by several effects: (i) a shunting effect due to the thick Cu buffer layer (ii) the existence of mixed region at the interfaces with a formation of a ternary CoZnCu phase. Such ternary CoZrCu alloy at the interfaces was already observed in sputtered CoZr/Cu/Co sandwiches [3]. We have shown that is possible to grow welldefined electrodeposited multilayers consisting of ferromagnetic CoxZn1x alloys separated by nonmagnetic Cu layer. With the interfacial effects we have explained the superparamagnetic magnetization behaviour and the fall of the magnetoresistance as compared to Co/Cu prepared by the same technique. This work has been supported by the PICS (Programme International de Coop!eration Scientifique) contracted between CNRST (Morocco) and IPCMSCNRS (France).
ARTICLE IN PRESS T. El Bahraoui et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
References [1] R.D.M. Michael, V. Atzmony, C. Beauchamp, L.H. Benne Swartzendruber, D.S. Lashmore, L.T. Romankiw, J. Magn. Magn. Mater. 113 (1992) 149. [2] H. El Fanity, K. Rahmouni, M. Bouanani, A. Dinia, G. Schmerber, C. M!eny, P. Panissod, A. Cziraki,
e957
F. Cherkaoui, A. Berrada, Thin Solid Films 318 (1998) 227. [3] M. El Harfaoui, M. Faris, A. Qachaou, J. Ben Youssef, H. Le Gall, D. Meziane Mtalsi, J. Magn. Magn. Mater. 223 (2001) 81.