Influences of pulse time and external magnetic on Giant Magnetoresistance (GMR) effect of multilayer Co/Cu were investigated. Results showed that by changing pulse deposition time (tCo, tCu), the MR ratio of the electrodeposited multilayers varied from 0 to 2.70%. The maximum value of MR ratio (2.70%) was achieved with deposition time (tCo= 2s, tCu= 5s), corresponding to the thickness (δCo = 2.1 nm, δCu= 7.0 nm). The presence of external magnetic field Hext during electrodeposition enhanced the amount of deposited Cu on one hand, and increased the (200) texture of the deposited films on the other hand. As a result, the MR ratio of the obtained multilayers increased slightly from 2.70% (Hext= 0) to 2.74% (Hext= 600 mT)

Nghi, Nguyen Hoang

Tung, Mai Thanh

Vietnam Academy of Science and Technology: Journals Online

97
Journal of Chemistry, Vol. 45 (1), P. 97 - 101, 2007 
Effect of pulse time and external magnetic field on 
Giant Magnetoresistance (GMR) Effect of 
electrodeposited Multilayer Co/Cu
Received 4 May 2006 
MAI THANH TUNG1, NGUYEN HOANG NGHI2
1Dep. of Electrochemistry and Corrosion Protection, Hanoi University of Technology 
2Lab. of Amorphous and Nanocrystalline Materials, Hanoi University of Technology 
 
SUMMARY 
 
Influences of pulse time and external magnetic on Giant Magnetoresistance (GMR) effect of 
multilayer Co/Cu were investigated. Results showed that by changing pulse deposition time (tCo, 
tCu), the MR ratio of the electrodeposited multilayers varied from 0 to 2.70%. The maximum value 
of MR ratio (2.70%) was achieved with deposition time (tCo = 2s, tCu = 5s), corresponding to the 
thickness (Co = 2.1 nm, Cu= 7.0 nm). The presence of external magnetic field Hext during 
electrodeposition enhanced the amount of deposited Cu on one hand, and increased the (200) 
texture of the deposited films on the other hand. As a result, the MR ratio of the obtained 
multilayers increased slightly from 2.70% (Hext= 0) to 2.74% (Hext= 600 mT). 
 
I - INTRODUCTION 
Magnetic multilayers have attracted 
considerable attention in magnetic sensor 
research due to their giant magnetoresistance 
(GMR) effect, which are characterized by 
changes of electrical resistance when magnetic 
field is applied [1, 2]. Usually, the multilayer 
materials are prepared by means of vapour 
deposition techniques, which are suitable for the 
controlled preparation of structures on atomic 
scales. Electrodeposition meanwhile is a 
promising technique for practical purpose due to 
its efficiency and simplicity of the required 
equipment [3 - 7]. In the previous studies, we 
have shown that the multilayers Co/Cu can be 
produced by electrodeposition routine [5, 6]. 
However, the GMR effect, which is mainly 
related to microstructure as well as microscopic 
growth process and electric transport inside the 
multilayers, is influenced by structure and 
magnetic properties of components and 
therefore decided by electrodeposition 
parameters. 
In this paper, the results on study influences 
of pulse deposition time and external magnetic 
field during electrodeposition on GMR effect of 
the electrodeposited multilayer Co/Cu will be 
presented. 
II - EXPERIMENTAL 
Electrodeposition of Co/Cu multilayers was 
performed in a citrate electrolyte containing 0.5 
M CoSO4, 0.05 M CuSO4, 0.035 M NaCl and 
0.2 M Na-citrate, pH 4 and at room temperature. 
The substrate used in the experiments is Si (111) 
coated by 10 nm film of Au (denoted as Si/Au) 
with resistively of 0.05 .cm. Prior to each 
experiment the Si/Au samples were sequentially 
ultrasonically cleaned in acetone, ethanol and 
water for 10 minutes. An ohmic contact was 
98
formed on the back side of the samples by 
applying InGa eutectic after treatment in 48% 
HF 1 min.  
The electrodeposition experiments were 
carried out in a conventional three electrode 
electrochemical cell with Pt counter electrode 
and saturated calomel electrode (SCE) 
connected to potentiostat Autolab (EcoChemie). 
The electrodeposition of Co/Cu was carried out 
by the pulse technique with ECo = -0.8 V, ECu =
-0.15 V and varied tCo and tCu (Fig. 1a). The 
thicknesses of the deposited Cu and Co films 
can be calculated from the intergration of the 
current-time curve (Fig. 1b) and the equation (2) 
[7].  
DS
M
nF
Q Me
Me
diss
Me .
.= (1) 
where deposition charge =
2
1
t
t
Me
dep IdtQ with I:
recorded current response (A), : thickness of 
the deposited metal (cm), n: number of electron, 
F: Faraday constant (C/mol), M: atomic weight, 
S: electrode surface (cm2), D: density (g/cm3). 
Since the obtained multilayers practically 
consist of Cu and Co-Cu alloy components (Co-
Cu/Cu), the thickness of Co layer was calculated 
with the approximation that M, D values of the 
Co-Cu component were taken from Co element 
(MCo = 59, DCo = 8.8 g/cm
3). 
 
20 30 40 50 60
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
(a)
deposition time (s)
P
o t
e n
t i a
l E
v s
S C
E
( V
)
20 30 40 50 60
-10
-8
-6
-4
-2
0
2
4 (b)
QCo
Cu Cu Cu CuCu
CoCo Co Co Co
QCu
Cu
Co
deposition time (s)
c u
r r
e n
t d
e n
s i
t y
/ m
A
/ c
m
²
Figure 1: (a) Potential pulse program for the electrodeposition, and (b) Current response for the 
electrodeposition of Cu/Co multilayer (tCo = 2s, tCu = 5s) 
 
In order to investigate the effect of external 
magnetic fields during the deposition process, 
uniform magnetic fields of up to 600 mT 
generated by an electromagnet were applied 
parallel to the electrode’s surface. The GMR 
effect was characterized by a four-point in-plane 
resistance measurement varying the field 
strength up to 250 Oe. The magneto resistance 
(MR) ratio is determined by equation: 
R
RMR = (2) 
where R is electrical resistance at zero magnetic 
field (H = 0), R is change of electrical 
resistance as external magnetic field H = 0. The 
crystal structure of the deposited Co/Cu was 
analyzed by X-ray diffraction with Co-K using 
a Philips diffractometer. 
III- RESULTS AND DISCUSSION 
1. Influence of pulse deposition time (tCo, tCu)
In order to investigate the influence of pulse 
time (tCo, tCu) on the GMR effect of the 
multilayer, the pulse time (tCu, tCo) was varied 
and MR curves of the obtained multilayer were 
recorded. It should be noted that the pulse 
potential time (tCo=2s; tCu=5s) (corresponding to 
(Co = 2.1 nm, Cu = 7.0 nm)) was chosen as the 
99
origin value, since with these thickness the 
theoretically calculated MR-ratio owned the 
highest value [2]. Figure 2 shows MR curves of 
the multilayers deposited at different pulse time 
(tCo, tCu) and the corresponding MR ratios of 
multilayers with different (tCo, tCu) are 
summarized in table 1. Results show that the 
maximum value of MR ratio is obtained with 
(tCo = 2s, tCu = 5s), corresponding to the 
thicknesses (Co= 2.1 nm, Cu = 7.0 nm). This 
result confirms the theoretical calculations, 
which indicated that with thickness Co = 2 nm 
and Cu = 7 nm, the highest MR ratio of the 
multilayer can be obtained due to the optimal 
magnetic and electric transports between layers 
[2].
 
-200 -100 0 100 200
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
tCo=2s, tCu=6s
tCo=2s, tCu=5s
tCo=2s, tCu=4s
tCo=2s, tCu=3s
tCo=2s, tCu=2s
tCo=2s
M
R
ra
tio
(%
)
H(Oe)
 
-200 -100 0 100 200
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
tCu=5s
tCo=7s, tCu=5s
tCo=6s, tCu=5s
tCo=3s, tCu=5s
tCo=4s, tCu=5s
tCo=5s, tCu=5s
H(Oe)
M
R
ra
tio
(%
)
Figure 2: MR curves of multilayers Co/Cu electrodeposited with different pulse time (tCo; tCu)
Table 1: Magnetoresistance ratio (MR) of multilayers Co/Cu deposited with different pulse time 
 
Pulse deposition time Co, nm Cu, nm MR, % 
tCo = 2s
tCo = 2s; tCu = 2s 2.0 3.0 0.56
tCo = 2s; tCu = 3s 2.0 3.7 1.29
tCo = 2s; tCu = 4s 2.0 5.6 1.42
tCo = 2s; tCu = 5s 2.1 7.0 2.71
tCo = 2s; tCu = 6s 2.2 7.5 2.23
tCu = 5s
tCu = 5s; tCo = 3s 5.2 2.4 0.91
tCu = 5s; tCo = 4s 5.3 3.1 0.56
tCu = 5s; tCo = 5s 5.3 4.5 0.29
tCu = 5s; tCo = 6s 5.2 6.0 0.08
tCu = 5s; tCo = 7s 5.1 6.9 0.00
2. Influence of external magnetic field Hext 
100
-1200 -1000 -800 -600 -400 -200 0 200 400 600
-10
-5
0
5
10
15
20
-150 -125 -100 -75 -50 -25
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
Cu disolution
Co disolution
Co deposition Cu deposition
i /
m
A
. c
m
- ²
Hext=600mT
H
ext
=0mT
E (SHE)/mV
 
Figure 3: Cyclic Voltammetric curves without external magnetic field (solid curve) and with 
external magnetic field Hext = 600 T (dash curve) 
 
Figure 3 displays the cyclovoltammogram 
of the substrate Si/Au without magnetic field 
(solid line) and with external magnetic field Hext 
= 600 mT (dashed line). A slight increase of the 
current density in the Cu deposition region in 
the presence of external magnetic field Hext can 
be observed in the magnified part of the 
polarization curve (inset in Fig. 3). In the back 
scan, Co dissolution peaks of both curves are 
nearly overlapped, while the amount of Cu 
dissolution is higher for the curve with external 
magnetic field (Fig. 3). This effect can be 
explained by the so-called magneto-
hydrodynamic effects (MHD) caused by a high 
convection in the electrolyte as a result of the 
Lorentz force [8]. Thus, the external magnetic 
field increases the amount of Cu deposition and 
affects only slightly on the deposition of Co. 
XRD pattern of the electrodeposited 
multilayers without magnetic field and with Hext 
= 600 mT is shown in Fig. 4. It can be observed 
that the electrodeposited multilayers consist of 
fcc phases ((111) and (100) textures) and bcc 
phase ((200) texture). However, the (200) 
texture of the multilayer deposited under 
external magnetic field is higher than that of the 
multilayer deposited without external magnetic 
filed Hext. Since the (200) texture enhances the 
magnetic properties of the Co components, it is 
expected that the GMR effect of the multilayer 
increases clearly as electrodeposition is carried 
out under external magnetic field [9]. However, 
the MR ratio increases only slightly when 
external magnetic field is applied during 
electrodeposition i.e MR(Hext=0) = 2.70 and 
MR(Hext=600mT) = 2.74 as shown in figure 5. This 
can be explained by the fact that the MR ratio in 
this case is mainly decided by the thickness of 
the Co and Cu layers. As shown in Fig. 3, the 
presence of Hext accelerates the deposition of Cu 
and thereby increases the thickness of Cu layers.  
 
35 40 45 50 55 60
Hext=600mT
(200)
(110)
(111)
Hext=0
I n
t e
n s
i t y
( a
. u
)
2 Theta (D egree)
 
Figure 4: XRD pattern of the electrodeposited 
multilayers Co(2.1 nm)/Cu(7.0 nm) (tCo = 2s; tCu 
= 5 s) with superimposed magnetic field H = 0 
and H = 600 T 
101
-200 -100 0 100 200
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Co(2.1nm)/Cu(7.0nm)
Hext = 600 mT
Hext = 0
M
R
r a
t i o
( %
)
H (Oe)  
Figure 5: MR curves of the electrodeposited 
multilayer Co(2.1 nm)/Cu(7.0 nm) (tCo = 2s; tCu =
5s) with external magnetic field H = 0 and         
H = 600 T 
Therefore, the effect of increasing Cu thickness 
is dominated comparing with the increase of the 
(111) texture and only small change of the MR 
ratio is obtained as a result when external 
magnetic field is applied during electro-
deposition. 
IV- CONCLUSIONS 
Giant Magnetoresistance (GMR) effect of 
the multilayer Co/Cu is influenced by pulse 
deposition time (tCo,tCu) and external magnetic 
field during electrodeposition. By changing 
pulse deposition time (tCo,tCu), the MR ratio of 
the electrodeposited multilayers varied from 0 to 
2.70%. The maximum value of MR ratio 
(2.70%) is achieved with deposition time (tCo =
2s, tCu = 5s), corresponding to the thickness (Co 
= 2.1 nm, Cu = 7.0 nm). The presence of 
external magnetic field Hext during 
electrodeposition enhances the amount of 
deposited Cu on one hand, and increases the 
(200) texture of the deposited films on the other 
hand. As a result, the MR ratio of the obtained 
multilayers increases slightly from 2.70% (Hext =
0) to 2.74% (Hext = 600 mT). 
Acknowledgements: We thank the Research 
Fund of VLIR-HUT Research Fund (Project Nr. 
VLIR-HUT/IUC/PJ10) for the financial support 
of this work. 
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Effect of pulse time and external magnetic field on Giant Magnetoresistance (GMR) effect of electrodeposited multilayer Co/Cu

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Effect of pulse time and external magnetic field on Giant Magnetoresistance (GMR) effect of electrodeposited multilayer Co/Cu

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