Journal of Magnetism and Magnetic Materials 272–276 (2004) e955–e957
Structural, magnetic and transport properties of CoZn/Cu electrodeposited multilayers
T. El Bahraoui a , H. Errahmani a , A. Berrada a, *, A. Dinia b , G. Schmerber b , F. Cherkaoui El Moursli c , F. Hajji c , H. Lassri d
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 (Co
9.7Zn
90.3/Cu)
20multilayers grown from electrochemical dual bath. X-ray diffraction patterns have shown that the CoZn structural lattice parameters are close to those of the monoclinic CoZn
13compound. 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 multi- layers 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 (Co
xZn
1x/Cu)
nmultilayers not studied until now and to investigate the structural, the magnetic and the transport properties.
The (Co
xZn
1x/Cu) multilayers have been grown using the electrodeposition technique by the dual bath.
The magnetic Co
xZn
1xlayer was deposited in the electrolyte bath containing CoCl
26H
2O; CoSO
47H2O;
ZnSO
47H
2O; (NH
4)
2SO
4and H
3BO
3.
The Cu layer was deposited during t=2 s for a current density of about 20 mA/cm
2in the electrolyte bath, which contains CuSO
45H
2O and H
2SO
4. The thickness of the CoZn alloy was fixed at 12 nm, whereas the Cu layer thickness was t
Cu=3 nm. The samples have been deposited on glass (or SiO
2) substrates, covered by a 240 nm thick Cu buffer layer sputter-deposited at room temperature. SEM observations have shown homoge- nous 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 mag- netoresistivity measurements have been used to char- acterize these samples.
Figs. 1a and b show X-ray, y22y; spectra recorded using CoK! a
1radiation (l=0.1789 nm) of the (Co
9.7Zn
90.3/Cu)
20and (Co
4.6Zn
95.4/Cu)
10multilayers.
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 CoZn
13phase. The presence of the first order satellites
ARTICLE IN PRESS
*Corresponding author. Tel./fax: +212-37-67-11-18.
E-mail address:
[email protected] (A. Berrada).
0304-8853/$ - see front matter
r2003 Published by Elsevier B.V.
doi:10.1016/j.jmmm.2003.12.266
(Fig. 1b), labelled SR
n1and SR
nþ1indicates 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 (Co
9.7Zn
90.3/Cu)
20multilayer. 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 contri- bution at small fields and superparamagnetic contribution at high fields. This is further con- firmed by the magnetoresistance (MR) curve reported in Fig. 3.
The MR(H) loop displays a broad, rounded max- imum 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 electrodepos- ited 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 well- defined electrodeposited multilayers consisting of ferromagnetic Co
xZn
1xalloys separated by non- magnetic Cu layer. With the interfacial effects we have explained the superparamagnetic magne- tization behaviour and the fall of the magnetore- sistance as compared to Co/Cu prepared by the same technique.
This work has been supported by the PICS (Pro- gramme International de Coop eration Scientifique) ! contracted between CNRST (Morocco) and IPCMS- CNRS (France).
ARTICLE IN PRESS
20 30 40 50 60 70 80 90
Cu (220)
(244) (402)
(220)
Angle 2Θ (degree)
Intensity (u. a.)
Cu (111)
Cu (200) CoZn13
CoZn13 CoZn13
CoZn13
CoZn13 (331) (400)
(a)
(Co9.7Zn90.3/ Cu)20
(402) Multilayer
Cu (111)
(b)
CoZn13
Substrat
satellites
Intensity (u. a.)
Angle (2Θ) (degree) [Co4.6Zn
95.4 / Cu]
10
20 30 40 50 60 70 80 90
Fig. 1. (a–b)
y22yspectra recorded for the (Co
4.6Zn
95.4/Cu)
20and (Co
9.7Zn
90.3/Cu)
20multilayers. The insert shows the multilayer peak (SR
n) and the first order satellites SR
n1and SR
nþ1:Magnetic field H(kOe)
M/ M0 (13kOe)
T=300K (Co9.7Zn90.3/ Cu)20
-1.0 -15 -0.5 0.5 1.0
0.0
-10 5 0 5 10 15
Fig. 2. Magnetization loop for the (Co
9.7Zn
90.3/Cu)
20multi- layer with the magnetic field in the film plane.
-15 -10 -5 0 5 10 15
0.00 0.05 0.10 0.15 0.20 0.25 0.30
[Co
9.7Zn
90.3/Cu]
20MR%
Magnetic field H(kOe)
T=300K
