Electrodeposition of CoNi and CoNiP alloys in sulphamate electrolytes

Article abstract of DOI:10.1016/j.jallcom.2010.05.032

Magnetic, mechanical and structural characterisation of CoNi and CoNiP electrodeposits has been performed. Bright fine-grained fcc soft-magnetic layers of CoNi have been obtained at the different current densities and bath temperatures used. Alloy formation improves the mechanical properties of coating respect to the single electrodeposited metals. The incorporation of phosphorous in CoNi deposits favoured the deposition process, which occurred at less negative potentials. Moderate phosphorous percentages were obtained but significant modifications in the structure and the magnetic properties were detected. Fcc or hcp CoNiP layers can be obtained as a function of deposition conditions, showing the hcp CoNiP the maximum coercivity values. Fcc CoNiP deposits showed the highest hardness values.

Full text of DOI:10.1016/j.jallcom.2010.05.032

Journal of Alloys and Compounds 503 (2010) 454–459
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Electrodeposition of CoNi and CoNiP alloys in sulphamate electrolytes
P. Cojocarua,∗, L. Magagnina, E. Gómezb, E. Vallésb
a Politecnico di Milano, Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”, Via Mancinelli, 7, 20131 Milano Italy
b Electrodep, Departament de Química Fısica and Institut de Nanociència i Nanotecnologia (IN2UB) de la Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Magnetic, mechanical and structural characterisation of CoNi and CoNiP electrodeposits has been per-
formed. Bright fine-grained fcc soft-magnetic layers of CoNi have been obtained at the different current
densities and bath temperatures used. Alloy formation improves the mechanical properties of coating
respect to the single electrodeposited metals. The incorporation of phosphorous in CoNi deposits favoured
the deposition process, which occurred at less negative potentials. Moderate phosphorous percentages
were obtained but significant modifications in the structure and the magnetic properties were detected.
Fcc or hcp CoNiP layers can be obtained as a function of deposition conditions, showing the hcp CoNiP
the maximum coercivity values. Fcc CoNiP deposits showed the highest hardness values.
© 2010 Elsevier B.V. All rights reserved.
Received 8 June 2009
Accepted 9 May 2010
Available online 19 May 2010
Keywords:
Electrodeposition
Cobalt–nickel alloys
X-ray diffraction
Microhardness
Magnetic properties
1. Introduction
trode surface during the alloy deposition process. Sulphamate
electrolytes seem to be more stable to pH changes than sulphate
Magnetic materials have received much attention in recent
years because their extensive technological applications in micro-
electronics industry. A particular research study was focused on
ferromagnetic materials [1–4].
and chloride electrolytes being sulphamate the preferred bath of
industry [11]. Deposits produced by chloride and sulphate baths
are exhaustively studied in the investigation ambits [12–15]. How-
ever, not much characterisation work exists for deposits obtained
from sulphamate bath.
In particular, the use of cobalt–nickel system has been extended
to some magnetic applications, especially in microsystems technol-
ogy for manufacture of sensors, actuators or inductors [5–7], and
their use has been tested as magneto-optic memory material as
very desirable data storage material [8,9]. Cobalt and nickel form a
solid solution fact that possibilities “to tailor” the alloy composition.
The nickel presence in the alloy although diminishes some cobalt
magnetic capabilities as magnetisation of saturation but improves
the hardness, making the alloy also useful to other different appli-
cations that demand both mechanic and environmental resistance.
Electrodeposition is a versatile low-cost method to obtain alloy
films, anditisgenerallycompatiblewiththefabricationofmagnetic
components in integrated devices. Furthermore, it allows precise
control over films properties and permits deposition of variable
geometries. The electrodeposition of cobalt–nickel alloy belongs
to the anomalous type [10], in which the less noble metal (Co) is
preferentially deposited, as the manner that the obtained deposits
contain much higher percentage of cobalt than in the solution.
The electrodeposition of cobalt–nickel alloy is accompanied by
coevolution of hydrogen that leads local pH rise near the elec-
This work was aimed to investigate at first cobalt–nickel depo-
sition in order to characterise the magnetic properties of deposits
obtained from sulphamate bath in presence of additives such sac-
charine, wetting agent and boric acid. We performed the CoNi
deposition at different current densities and temperatures. The
dependency on crystallinity, surface morphology and microhard-
ness was discussed. Also the incorporation of phosphorous in the
alloy will be analyzed. CoNiP ternary alloy deposits will be pre-
pared at similar conditions of those of CoNi, in order to compare
the effect of phosphorous presence on the deposition process and
to analyze the properties of the obtained deposits. Moreover, the
evaluation of the possibility to extend the results obtained from
lab-three-electrode system to and industrial ambit will be tested.
2. Experimental procedure
A
sulphamate electrolytic bath (CoNi solution) was developed for CoNi
deposits preparation (55 g/l nickel sulphamate + 20 g/l cobalt sulphamate + 35 g/l
H3BO3 + 1.5 g/l saccharine + 0.15 g/l SDS) using sodium dodecylsulphate (SDS) as
wetting agent and saccharine as antistressing agent. Ternary CoNiP alloys were
simultaneously prepared in similar conditions adding sodium hypophosphite as a
source of phosphorous. All the solutions were prepared using water treated with a
Millipore Milli Q system. The solution pH was adjusted to 4 using NaOH solution.
Electrodeposits were prepared galvanostatically at different current densities and
temperatures. Plating solution in a 300 ml cell was mechanically stirred (200 rpm)
using a mechanical stirrer. A programmable EG&G galvanostat/potentiostat was
∗
Corresponding author. Tel.: +39 0223993150; fax: +39 0223993180.
E-mail address: paula.cojocaru@polimi.it (P. Cojocaru).
0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2010.05.032

P. Cojocaru et al. / Journal of Alloys and Compounds 503 (2010) 454–459
455
Table 1
Composition of CoNi electrodeposits as a function of the bath temperature and
current density applied.
mA cm−2
◦C
at.% Ni
at.% Co
−10
−30
−50
−10
−10
50
50
50
40
30
47.0
54.2
55.3
44.2
40.2
53.0
45.8
44.7
55.8
59.8
Few variations in the morphological, structural and mechani-
cal properties of the CoNi deposits were observed for the different
deposition conditions tested. Compact, no fragile and very fine-
grained CoNi deposits were always obtained, which morphology
was hardly detected from SEM observation (Fig. 2).
XRD results agree with those obtained from SEM micrographs,
wide peaks were detected being the calculated grain sizes using
Debye–Scherrer equation around 13 nm. All CoNi deposits prepared
showed diffraction peaks corresponding to an fcc structure (Fig. 3).
No differences were observed in the range of current densities and
temperatures used. The position of the peaks of the fcc phase was
shifted to lower ꢁ values than those corresponding to pure nickel as
a consequence of the incorporation of cobalt in the fcc crystalline
lattice. The intermediate position of the peaks between those of
cobalt fcc and nickel fcc reveal the formation of solid solution of
both metals.
Fig. 1. E–t transients of CoNi electrodeposition at different current densities (j in
mA cm−2) and temperatures (◦C) (a) j = −10, T = 50, (b) j = −30, T = 50, (c) j = −50,
T = 50, (d) j = −10, T = 40, (e) j = −10, T = 30.
used with Ag/AgCl as reference electrode and a commercial nickel–sulphur anode
as counterelectrode. Deposits 10 ␮m thick were obtained over inox steel substrate
polished with grit paper prior the electrodeposition. Samples were detached of the
substrate for posterior characterisation. For all conditions samples were prepared
in triplicate in order to assure reproductibility.
Elemental analysis of the deposits was performed with a Fischerscope X-ray XAN
and confirmed with a scanning electron microscope Zeiss EVO 50 equipped with
microanalysis. Deposit morphology was observed using Hitachi S 2300 scanning
electron microscope.
The phase analysis of the deposits was studied by X-ray powder diffractometry
(XRD), using a Siemens D-500 diffractometer in conventional Bragg–Brentano con-
figuration. The Cu K␣ radiation (ꢀ = 1.5418 Å) was selected using a diffracted beam
curved graphite monochromator. The X-ray powder diffraction diagrams were mea-
sured in the 5–100◦ 2ꢁ range with a step range of 0.05◦ and a measuring time of 15 s
per step.
Coatings were characterised in terms of micromechanical properties. Vickers
microhardness (HV) data were obtained from penetration depth-load curves by
means of a Fischerscope® H100 microhardness measurement system. Measure-
ments conditions were as follows: 250 mN peak load, 10 s loading/unloading time
and 5 s holding time at peak load. The reported values are the average of 5 measure-
ments taken on three different samples prepared in the same conditions from the
same bath.
Determination of both HV hardness and Young’s modulus was
made acquiring measurements on the surface and on the cross
section of the films detached. The results show that no signifi-
cant variation was observed for the alloy deposits as a function
of the applied current density. The obtained microhardness values
ranged between 533–547 HV with standard deviation SD ≈ 20. In
order to compare the mechanical properties of alloy and pure met-
als, the electrodeposition of both nickel and cobalt was performed
from the sulphamate bath containing the corresponding metal in
the same operating parameters. Microhardness of obtained CoNi
alloy improved: microhardness values were higher than those cor-
responding to electrodeposited nickel (337 HV with SD ≈ 24) and
electrodeposited cobalt (450 HV with SD ≈ 15).
When mechanical properties of the coatings prepared at differ-
ent temperatures were analyzed, a gradual variation of the values
was observed as a function of the deposition temperature. Fig. 4
shows that when the deposition temperature decreases, both the
micro hardness and Young’s modulus decrease. The maximum
Magnetic properties were characterised by means of a SQUID magnetometer at
room temperature. Magnetisation vs magnetic field curves of the different samples
placed parallel to the magnetic field was recorded.
3. Results and discussion
3.1. Characterisation of CoNi coatings
Films of CoNi were prepared from CoNi solution at different
temperatures and current densities. Galvanostatic curves reveal
the logical dependences of the stabilisation potential as a func-
tion of both current density and temperature (Fig. 1). Stabilisation
potentials were more negative by applying more negative current
densities. At fixed current density (−10 mA cm−2) an increase in the
temperature advanced the deposition potential.
Anomalous CoNi deposition was observed for all conditions
tested (Table 1) as is usual in the CoNi system from different elec-
trolytic baths used [16,17]. At fixed current density a low decrease
of the cobalt percentage was observed when temperature was
increased. On the other hand, an increase of the current density
favoured the decrease of the cobalt percentage. This behaviour
corresponds to a nickel deposition process controlled by activa-
tion whereas cobalt deposition process can be controlled by mass
transfer as in other media [18].
Fig. 2. SEM picture of a CoNi deposit obtained at j = −10 mA cm−2, T = 50 ◦C.

456
P. Cojocaru et al. / Journal of Alloys and Compounds 503 (2010) 454–459
Fig. 3. Two details of the X-ray diffractograms of CoNi deposits obtained at 50 ◦
C
and: curve (a) j = −10 mA cm−2, curve (b) j = −50 mA cm−2
.
Fig. 5. Magnetisation vs magnetic field applied for CoNi samples prepared at:
(A) j = −10 mA cm−2, T = 50 ◦C, (B) j = −50 mA cm−2, T = 50 ◦C, (C) j = −10 mA cm−2
,
T = 40 ◦C.
hardness (up to 533 HV) and minimum elasticity (98 GPa) was
observed for CoNi prepared at the higher temperature used.
In order to study the magnetic properties of alloy prepared, the
magnetisation vs applied magnetic field curves were recorded. For
all current densities and temperatures used, soft-magnetic prop-
erties of the films were detected (Fig. 5). All deposits showed very
low coercivity values lower than 10 Oe. The magnetisation of sat-
uration value decreased (from 117 emu g−1 for deposits of 55 at.%
Co to 107 emu g−1 for deposits with 45 at.% Co) as the cobalt con-
tent decreased due to the lower saturation magnetisation of pure
electrodeposited nickel (52 emu g−1) with respect to pure elec-
trodeposited cobalt (150 emu g−1).
3.2. Characterisation of CoNiP coatings
In order to study the effect of phosphor incorporation on the
deposit’s properties (morphology, structure, mechanical and mag-
netic) this work was focused in electrodeposition of CoNiP alloys.
Ternary CoNiP layers were prepared also galvanostatically from the
CoNi solution by adding 2.5 g/l sodium hypophosphite as phosphor
source. Applied current density and temperature values were those
previously used for CoNi preparation.
Galvanostatic curves reveal (Fig. 6) the same gradual depen-
dence of the stabilisation potential as a function of both current
density and temperature than the recorded during CoNi prepara-
Fig. 4. Dependence of the microhardness (A) and Young’s modulus (B) with the
temperature for CoNi deposits obtained at j = −10 mA cm−2
.

P. Cojocaru et al. / Journal of Alloys and Compounds 503 (2010) 454–459
457
Fig. 7. SEM picture of a CoNiP deposit obtained at j = −10 mA cm−2, T = 50 ◦C.
Fig. 6. E–t transients of CoNiP electrodeposition for different current densities (j in
mA cm−2) and temperatures (◦C). CoNi solution + 2.5 g/l sodium hypophosphyte. (a)
j = −10, T = 50, (b) j = −30, T = 50, (c) j = −50, T = 50, (d) j = −10, T = 40, (e) j = −10, T = 30.
slightly shifted to higher ꢁ values respect to those corresponding
to pure cobalt, as a consequence of nickel or nickel + phosphorous
incorporation in the crystalline lattice of the cobalt phase (Fig. 8B).
A certain texture was observed with a 0 0 2 preferred orientation.
A correlation between the crystalline structure and mechani-
cal behaviour of CoNiP films was found. Phosphorus incorporation
led to a slight increase of both HV hardness and Young’s modu-
lus, although the tendencies with current density and temperature
were similar to those observed for pure CoNi deposits. At fixed
deposition temperature, the nickel-rich deposits showing fcc struc-
ture presented the highest values of hardness (631 HV with SD ≈ 6).
tion. Stabilisation potentials were more negative by applying more
negative current densities. At fixed current density (−10 mA cm−2
)
an increase of temperature advanced the deposition potential.
However, the presence of hypophosphite in the solution led to a
shift of the deposition stabilisation to less negative values respect
to those recorded for CoNi parallel deposit, revealing that the incor-
poration of some phosphorous in the deposit favour the deposition
process.
The presence of hypophosphite in the bath induced phospho-
rous incorporation in the deposits. In all cases, ternary CoNiP
deposition took place, although low incorporation of phosphorous
in the deposits was observed (Table 2). In the most conditions,
deposits were richer in cobalt revealing that anomalous codepo-
sition between nickel and cobalt was maintained in the presence
of hypophosphite in the solution and the dependence of cobalt per-
centage with temperature was similar than for the binary CoNi
deposits. However, normal deposition occurs at −10 mA cm−2 and
50 ◦C.
The CoNiP deposits obtained were compact and fine grained
(Fig. 7), but a slight increase in the grain size was observed respect
to the corresponding CoNi ones as a consequence of phosphorous
incorporation.
Structural modifications were observed in the deposits obtained
in the presence of hypophosphite respect to those obtained
from free-hypophosphite bath, although crystalline deposits were
obtained. The films containing highest nickel percentages pre-
sented diffraction peaks assigned to CoNi fcc structure, although
the phase was slightly distorted by the presence of the phospho-
rous and a clear 111 preferred orientation was observed (Fig. 8A).
An increase of the estimated grain size up to 22 nm was observed.
CoNiP deposits with higher cobalt percentages showed an hcp
structure with grain size of around 18 nm. The reflexion peaks
Table 2
Composition of CoNiP electrodeposits as a function of the bath temperature and
current density applied.
mA cm−2
◦C
at.% Ni
at.% Co
at.% P
−10
−30
−50
−10
−10
50
50
50
40
30
67.5
44.6
45.1
41.4
33.4
28.7
53.6
53.3
55.5
64.0
3.8
1.8
1.6
3.1
2.6
Fig. 8. X-ray diffractograms of CoNiP deposits obtained at 50 ◦
C and: (A)
j = −10 mA cm−2, (B) j = −50 mA cm−2
.

458
P. Cojocaru et al. / Journal of Alloys and Compounds 503 (2010) 454–459
Fig. 9. Dependence of the microhardness (A) and Young’s modulus (B) with the
temperature for CoNiP deposits obtained at −10 mA cm−2
.
By increasing the current density, microhardness decrease and val-
ues of around 530 HV were obtained.
When temperature was increased the Young’s modulus
increases up to 175 GPa (Fig. 9). An important increase of the
Young’s modulus and microhardness was observed respect to those
measured for the corresponding CoNi deposits.
CoNiP nickel-rich deposits were compact and consistent and no
damage of the films was observed by detaching the layer from the
substrate. However, the other CoNiP deposits prepared were frag-
ile because they easily break down when were detached from the
substrate.
Fig. 10. Magnetisation vs magnetic field applied for different CoNiP samples
prepared at fixed temperature (50 ◦C) at: (a) j = −10 mA cm−2, fcc structure, (b)
j = −50 mA cm−2, hcp structure.
The influence of the phosphorous incorporation in the magnetic
properties of CoNi deposits was studied by recording magnetisation
vs magnetic field curves of coatings prepared at different temper-
ature and current densities. Magnetic curves reflected the change
in the crystalline structure observed from XRD characterisation.
Deposits with hexagonal phase showed higher values of both coer-
civity and magnetic susceptibility (Fig. 10).
The comparison of the magnetic properties of the binary CoNi
and ternary CoNiP deposits showed that, even maintaining both
the cobalt percentage in the deposits and the structural phase (fcc),
ternary deposits loose the soft-magnetic behaviour and lowered
the susceptibility value observed for CoNi binary deposits prepared
at similar deposition conditions (Fig. 11). It seems that the phos-
phorous presence hinders the magnetic domain orientation.
In order to extend the study of industrial application, paral-
lel experiments were made using a two-electrode system in a
tank-cell. The results obtained a lab-scale (three-electrode elec-
trochemical system) have been validated. For the baths studied,
the use of the electrochemical system of two-electrodes, led
to the same compositional dependences with both the tem-
perature and the current density than those obtained using
the system of three electrodes. Moreover, CoNi and CoNiP
coatings obtained by electrodeposition was involved in the
Fig. 11. Magnetisation vs magnetic field applied graph for CoNi (curve a) and CoNiP
(curve b) deposits obtained in the same conditions (j = −10 mA cm−2, T = 40 ◦C).

P. Cojocaru et al. / Journal of Alloys and Compounds 503 (2010) 454–459
459
fabrication (industrial scale) of optic shell for space applica-
Acknowledgement
tions.
EG and EV wish to thank the financial support by contract
MAT2006-12913-C02-01 from the Comisión Interministerial de
Ciencia y Tecnología (CICYT) of Spain.
4. Conclusions
From the sulphamate bath used, CoNi layers of several microns
were compact and fine grained, showing a clear soft-magnetic
behaviour with different saturation of magnetisation as a function
of their cobalt percentage. No significant variation in their proper-
ties was observed when they were prepared from different current
densities or temperatures, which led to prepare soft-magnetic non
fragile films in a wide range of experimental conditions.
References
[1] B. Lochel, A. Maciossek, J. Electrochem. Soc. 143 (1996) 3343–3348.
[2] T. Wang, A.B. McCandless, R.M. Lienau, K.W. Kelly, D. Hensley, Y. Desta, Z.G.
Ling, J. Microelectromech. Syst. 14 (2005) 400–409.
[3] S. Guan, B.J. Nelson, J. Microelectromech. Syst. 15 (2006) 330–337.
[4] R.D. Noce, N. Barelli, R.F.C. Marques, P.T.A. Sumodjo, A.V. Benedetti, Surf. Coat.
Technol. 202 (2007) 107–113.
Clear modifications in both magnetic and mechanical properties
of CoNi electrodeposits have been observed when hypophosphite
was added to the electrodeposition solutions and phosphorous was
incorporated in the deposits, although a low phosphorous percent-
age has been detected in the CoNiP layers. Soft-magnetic behaviour
is lost in the presence of phosphorous, especially when the crys-
talline phase varied from fcc to hcp one and the susceptibility of the
films could be modulated. Then, the electrodeposition of CoNi from
sulphamate bath but in the presence of sodium hypophosphite
allows modulating the magnetic properties of the CoNi layers.
CoNi coating improve the mechanical properties of pure cobalt
and pure nickel electrodeposits up to 533 HV. The phosphorous
incorporation increases the HV values of the films, but fragility of
the coatings was observed. However, fcc CoNiP deposits present
higher compactness than hcp ones.
[5] Y. Sverdlov, Y. Rosenberg, Y.I. Rozenberg, R. Zmood, R. Erlich, S. Natan, Y.
Shacham-Diamand, Microelectron. Eng. 76 (2004) 258–265.
[6] S. Guan, B.J. Nelson, J. Electrochem. Soc. 152 (2005) C190–C195.
[7] J. Casals-Terré, M. Duch, J.A. Plaza, J. Esteve, R. Pérez-Castillejos, E. Vallés, E.
Gómez, Sens. Actuators A 147 (2008) 600–606.
[8] J.N Hilfiker, D.W. Glenn, S. Heckens, J.A. Woollam, K.W. Wierman, J. Appl. Phys.
79 (1996) 6193.
[9] Z.Q. Zou, H. Wang, J. Zhou, D.F. Shen, Y.P. Lee, Eur. Phys. J. B 45 (2005) 97–102.
[10] A. Brenner, Electrodeposition of Alloys. Principles and Practice, Academic Press,
New York, 1963.
[11] S. Goldbach, R. de Kermadec, F. Lapicque, J. Appl. Electrochem. 30 (2000)
277–284.
[12] C. Fan, L. Piron, Electrochim. Acta 41 (1996) 1713–1719.
[13] N. Zech, E.J. Podlaha, D. Landolt, J. Electrochem. Soc. 146 (1999) 2886–2891.
[14] L. Burzynska, E. Rudnik, Hidrometallurgy 54 (2000) 133–149.
[15] C.K. Chung, R.X. Zhou, W.T. Chang, Microsyst. Technol. 14 (2008) 1279–1284.
[16] V.D. Jovic, N. Tosic, M. Stojanovic, J. Electroanal. Chem. 420 (1997) 43–51.
[17] E. Gómez, J. Ramírez, E. Vallés, J. Appl. Electrochem. 28 (1998) 71–79.
[18] C. Fan, D.L. Piron, Electrochim. Acta 41 (1996) 1713–1719.