Aftabi, A.

Alemipour, Z.

Najafi, M.

Rastegar Barmachi, N.

Soltanian, S.

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 4, 04MFPN09(3pp) (2012)   2304-1862/2012/1(4)04MFPN09(3) 04MFPN09-1  2012 Sumy State University The Effect of Diameter and Thermal Treatment on Magnetic Properties of  Co1-xZnx Alloy Nanowires  M. Najafi1,*, N. Rastegar Barmachi2,†, S. Soltanian2,‡, Z. Alemipour2,§, A. Aftabi2,**  1 Department of Materials Engineering, Hamedan University of Technology (HUT), Hamedan, Iran 2 Department of Physics, University of Kurdistan, Sanandaj, Iran  (Received 19 June 2012; published online 24 August 2012)  Nanowire arrays of the alloy, Co1−xZnx (0  x  0.2), with 20 and 35 nm diameters have been fabricated by the electrochemical deposition method into pores of anodized aluminum oxide (AAO) templates. Sam-ples with different composition could be obtained by adjusting the concentration ratio of Co2+ and Zn2+ in the solution of the electrolyte. The structure and magnetic properties were characterized by scanning elec-tron microscopy (SEM), atomic force microscopy (AFM) and alternating gradient force magnetometer (AGFM). It is found that the magnetic properties of the arrays are critically dependent on the compositions and diameter and thermal treatments. We found that the optimized composition for Co1−xZnx nanowire is around Co90Zn10 with 20 nm diameter annealed at 575 C in which the coercivity (Hc  2120 Oe) and squareness (Mr/Ms=0.98) have their maximum values consistently.  Keywords: Nanowire, AAO Template, Magnetic Property, Thermal Treatment.   PACS numbers: 75.75.Cd, 78.67.Uh                                                             * mojgannajafi1@gmail.com † breeze.nasim@gmail.com  ‡ s.soltanian@gmail.com  § zalemipour@yahoo.com  ** aftabi_a@yahoo.com  1. INTRODUCTION  There are many different types of nanowires that promising us to used them in near future to link of tiny pieces in very small circuits [1]. Electrodepositing the magnetic metal wires with nanoscale into the porous anodic aluminum oxide (AAO) templates have been utilized previously by many groups to prepare the one-dimensional nanostructure [1–3]. Anodic alumina oxide (AAO) template has been widely used to prepare nan-owire arrays because of its self-organized, tunable pore dimensions over a wide range of diameters and lengths, good mechanical strength and thermal stability. AAO template fabricated in process of Anodize in optimal condition. In this work, we synthesis Co1-xZnx nonowires with 20 and 35 nm diameter and effect of annealing on magnetic properties of nanowires investi-gated.  2. EXPERIMENTAL  Porous anodic aluminum oxide template were fabri-cated by two step anodize process [7]. For this purpose aluminum foil with high purity (99.999) and thickness of 0.3 mm were prepared. After annealed at 450 C for about 20 min in Ar-He to remove the oxide layer on surface of aluminum sample were used NaOH solution for 5 minutes then a mirror surface was achieved by electro-polishing in a 1:4 solution of H2ClO4 and C2H5OH at voltage of 20 V at room temperature. With use of electro-polish process to decrease roughness of Al surface. The first anodizing was performed according to table 1 in 0.3 M acids. The formation of pours in this process is completely randomized so created  templates have not a suitable ordering. So after the first anodize the oxide layer created during first anodize was re-moved within a chemical process in solution of 0.5 M phosphoric acid and 0.2 M chromic acid at temperature of 70 C. To achieve a relatively regular structure with hexagonal arrangement sample again in a similar con-dition with first anodize, re-anodized the samples. The thick aluminum oxide in the bottom of pores is an insu-lator barrier to fill them by electrodeposion of metals.  Table 1 –  condition of fabricated of AAO  Acid Sulfuric oxalic Duration of 1st anodize (h) 7 15 Duration of chemical removing (h) 10 15 Duration of 2nd anodize (h) 5.0 1 Voltage(v) 20 40 Temperature (oC) 1 14-15  Immediately after the second anodization the thick-ness of oxide layer in bottom of holes decrease. Per-fumed anodize at low voltages the perfect solution to decrease thickness of barrier layer [8] so voltage step to step reduced to 8 V. After preparation of template by AC electrochemical deposition method for 3 min with a frequency of 200 HZ and peak to peak voltage of 30 V Co1-xZnx (x  0, 0.01. 0.05, 0.1, 0.15, 0.2) nanowires al-loy fabricated in AAO template. For electro deposition of sample was used Cobalt Sulfate (CoSO4) and Zinc sulfate (ZnSO4).  In order to check for annealing effects on Co1-xZnx nanowire arrays, all the samples are annealed at dif-ferent temperatures 200, 300, 400, 450, 500, 550 and 575 C, respectively in Ar atmosphere. The magnetic properties of sample with draw the hysteresis loop by  M. NAJAFI, N. RASTEGAR BARMACHI, S. SOLTANIAN PROC. NAP 1, 04MFPN09(2012)    04MFPN09-2 AGFM were studied. The fine structure of nanowires by resolving of AAO in NaOH 1M solution by SEM was studied.  3. RESULTS AND DISCUSSION  By electropolish of Al samples the height of rough-ness decrease from 250 nm to 3 nm. AFM image of the surface before and after of electropolish was shown in Fig. 1. The mirror–like surface is suitable to fabricate of highly ordered porous anodic aluminum oxide.    Fig. 1 – AFM of Surface of the Al foil (a) before and (b) after the electropolish  To improve the ordering of the surface side of the anodic porous alumina, two-step anodization is effec-tively adopted After the removal of the oxide, an array of highly ordered dimples was formed on the Al, and these dimples can act as initiation sites for the hole development in the second anodization. The AFM view of surface for anodization with acid sulfuric after re-move the oxide layer in first anodization was shown in Fig. 2. SEM image of AAO template after second ano-dization in sulfuric was seen in Fig. 3.    Fig. 2 – SEM AFM image of Surface of the AAO after remove the oxide layer in first anodization in sulfuric acid   Fig. 3 – SEM image of surface of AAO after 2nd anodization in sulfuric acid  SEM image of synthesized nanowires with diameter of 20 and 35 nm are shown in Fig. 4.     Fig. 4 – a) SEM image of nanowires with 35 nm diameters and 2.1 mm length and (b) with 20 nm diameter and 2.5 mm  length  The coercivity and squareness of the samples are showed in Fig. 5. It can be seen coercivity of nanowires with 20 and 35 nm diameter by addition of impurities zinc in the electrolyte of electro deposition. The coer-cively decreases because Zinc atoms replaces to cobalt atoms and reduce magnetic properties. The regular increase coercivity with decreasing diameter was shown with Comparison two curves with 20 and 35 nm.   0.00 0.05 0.10 0.15 0.2020040060080010001200140016001800Hc(Oe)Concentration of Zinc (M) sulfuric(diameter:20nm) oxalic(diameter:35)  Fig. 5 – Coercivity of nanowires with diameters of 20 and 35 nm  Coersivity field of nanowires with diameters of 20 nm and 35 nm when increase zinc in electrolyte of electro deposition, decrease from 1711 Oe to 260 Oe and from 1500 to 270 Oe respectively. The effect of an-nealing temperature of samples with diameter of 20 and 35 nm on coercivitiy was examined in Fig. 6. It is supposed the loss of tension in annealing process is the reasons to improve the coercivity. The most coersivity  THE EFFECT OF DIAMETER AND THERMAL TREATMENT… PROC. NAP 1, 04MFPN09 (2012)   04MFPN09-3 (Hc  2120 Oe) related to sample with 10 percentage (x  1) of zinc in electrodeposition electrolyte with di-ameter of 20 nm. Fig. 7 is shown squareness of samples before and after the annealing. The most change in both diameters is related to the sample with x  5 after annealing in 575 C.  0.00 0.05 0.10 0.15 0.202004006008001000120014001600180020002200Hc (Oe)concentration of zinc (M) as prepared 2000c 3000c 4000c 4500c 5000c 5500c 5750c  0.00 0.05 0.10 0.15 0.202004006008001000120014001600Hc(Oe)concentration of zinc(M) as prepared 2000 c 3000 c 4000 c 4500 c 5000 c 5500 c 5750 c  Fig. 6 – The coercivity of Co1-xZnx nanowires with diameter of (a)20 nm and (b) 35 nm as a function of percentage of Zn and annealing temperature   4. CONCLUSIONS  In this paper the nanowires of Co1-xZnx with 20 and 35 nm fabricated by electrodeposition method and coer-sivity field decrease by increasing of Zinc but annealing in 575 C causes the magnetic properties of nanowires clearly increase. The highest coercivity and squareness after annealing related to Co90Zn10 (Hc  2120 Oe) and Co95Zn5 (sq  1),respectively.  0.00 0.05 0.10 0.15 0.200.740.760.780.800.820.840.860.880.900.920.940.960.981.00Mr/Msconcentration of zinc(M) as prepared  5750 c  0.00 0.05 0.10 0.15 0.200.50.60.70.80.91.0Mr/Msconcentration of zinc (M) as prepared 5750 c  Fig. 7 – Squareness of nanowires with (a) 20 nm and (b) 35 nm diameter to concentration of zinc (M) before and after annealing in 575 C  AKNOWLEDGEMENT  The authors are grateful for the financial support from the Grant Research Councils of HUT and Univer-sity of Kurdistan.     REFERENCES  1. L. Sun, P.C. Seatson, C.L. Chien, J. Magn. Magn. Mater. 49, 79 (2005)  2. Y. Zhou, C. Shen, H.  Li, Solid State Ionics 146, 81 (2002)  3. J.P. Pauzauskie, P.D. Yang, Mater. Today 9, 36 (2006)  4. D. Routkevitch, A. Tager, A. Haruyama, D. Almawlawi,  D. Moskovits, IEEE Trans. Electron. Dev. 146, 1646 (1996). 5. W. Lee, C.A. Ross, U. Gosele, K. Nielsch, J. Appl. Phys. 2, 978 (2006)  6. Y. Ren, S.L. Li, J.B. Wang, X.H. Han, J. Magn. Magn. Ma-ter. 321, 226 (2009)  7. H. Masuda, K. Fukuda, Science 268,1466 (1994) 8. A. Saedi, M. Ghorbani, Mater. Chem. Phys. 91, 417 (2005)   (a) (b) 

The Effect of Diameter and Thermal Treatment on Magnetic Properties of Co1-xZnx Alloy Nanowires

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 4, 04MFPN09(3pp) (2012) 
 
 
2304-1862/2012/1(4)04MFPN09(3) 04MFPN09-1  2012 Sumy State University 
The Effect of Diameter and Thermal Treatment on Magnetic Properties of  
Co1-xZnx Alloy Nanowires 
 
M. Najafi1,*, N. Rastegar Barmachi2,†, S. Soltanian2,‡, Z. Alemipour2,§, A. Aftabi2,** 
 
1 Department of Materials Engineering, Hamedan University of Technology (HUT), Hamedan, Iran 
2 Department of Physics, University of Kurdistan, Sanandaj, Iran 
 
(Received 19 June 2012; published online 24 August 2012) 
 
Nanowire arrays of the alloy, Co1−xZnx (0  x  0.2), with 20 and 35 nm diameters have been fabricated 
by the electrochemical deposition method into pores of anodized aluminum oxide (AAO) templates. Sam-
ples with different composition could be obtained by adjusting the concentration ratio of Co2+ and Zn2+ in 
the solution of the electrolyte. The structure and magnetic properties were characterized by scanning elec-
tron microscopy (SEM), atomic force microscopy (AFM) and alternating gradient force magnetometer 
(AGFM). It is found that the magnetic properties of the arrays are critically dependent on the compositions 
and diameter and thermal treatments. We found that the optimized composition for Co1−xZnx nanowire is 
around Co90Zn10 with 20 nm diameter annealed at 575 C in which the coercivity (Hc  2120 Oe) and 
squareness (Mr/Ms=0.98) have their maximum values consistently. 
 
Keywords: Nanowire, AAO Template, Magnetic Property, Thermal Treatment. 
 
 PACS numbers: 75.75.Cd, 78.67.Uh 
 
 
                                                          
* mojgannajafi1@gmail.com 
† breeze.nasim@gmail.com  
‡ s.soltanian@gmail.com  
§ zalemipour@yahoo.com  
** aftabi_a@yahoo.com  
1. INTRODUCTION 
 
There are many different types of nanowires that 
promising us to used them in near future to link of tiny 
pieces in very small circuits [1]. Electrodepositing the 
magnetic metal wires with nanoscale into the porous 
anodic aluminum oxide (AAO) templates have been 
utilized previously by many groups to prepare the one-
dimensional nanostructure [1–3]. Anodic alumina oxide 
(AAO) template has been widely used to prepare nan-
owire arrays because of its self-organized, tunable pore 
dimensions over a wide range of diameters and lengths, 
good mechanical strength and thermal stability. AAO 
template fabricated in process of Anodize in optimal 
condition. In this work, we synthesis Co1-xZnx 
nonowires with 20 and 35 nm diameter and effect of 
annealing on magnetic properties of nanowires investi-
gated. 
 
2. EXPERIMENTAL 
 
Porous anodic aluminum oxide template were fabri-
cated by two step anodize process [7]. For this purpose 
aluminum foil with high purity (99.999) and thickness 
of 0.3 mm were prepared. After annealed at 450 C for 
about 20 min in Ar-He to remove the oxide layer on 
surface of aluminum sample were used NaOH solution 
for 5 minutes then a mirror surface was achieved by 
electro-polishing in a 1:4 solution of H2ClO4 and 
C2H5OH at voltage of 20 V at room temperature. With 
use of electro-polish process to decrease roughness of Al 
surface. The first anodizing was performed according to 
table 1 in 0.3 M acids. The formation of pours in this 
process is completely randomized so created  templates 
have not a suitable ordering. So after the first anodize 
the oxide layer created during first anodize was re-
moved within a chemical process in solution of 0.5 M 
phosphoric acid and 0.2 M chromic acid at temperature 
of 70 C. To achieve a relatively regular structure with 
hexagonal arrangement sample again in a similar con-
dition with first anodize, re-anodized the samples. The 
thick aluminum oxide in the bottom of pores is an insu-
lator barrier to fill them by electrodeposion of metals. 
 
Table 1 –  condition of fabricated of AAO 
 
Acid Sulfuric oxalic 
Duration of 1st anodize (h) 7 15 
Duration of chemical removing 
(h) 
10 15 
Duration of 2nd anodize (h) 5.0 1 
Voltage(v) 20 40 
Temperature (oC) 1 14-15 
 
Immediately after the second anodization the thick-
ness of oxide layer in bottom of holes decrease. Per-
fumed anodize at low voltages the perfect solution to 
decrease thickness of barrier layer [8] so voltage step to 
step reduced to 8 V. After preparation of template by 
AC electrochemical deposition method for 3 min with a 
frequency of 200 HZ and peak to peak voltage of 30 V 
Co1-xZnx (x  0, 0.01. 0.05, 0.1, 0.15, 0.2) nanowires al-
loy fabricated in AAO template. For electro deposition 
of sample was used Cobalt Sulfate (CoSO4) and Zinc 
sulfate (ZnSO4).  
In order to check for annealing effects on Co1-xZnx 
nanowire arrays, all the samples are annealed at dif-
ferent temperatures 200, 300, 400, 450, 500, 550 and 
575 C, respectively in Ar atmosphere. The magnetic 
properties of sample with draw the hysteresis loop by 
 M. NAJAFI, N. RASTEGAR BARMACHI, S. SOLTANIAN PROC. NAP 1, 04MFPN09(2012)  
 
 
04MFPN09-2 
AGFM were studied. The fine structure of nanowires by 
resolving of AAO in NaOH 1M solution by SEM was 
studied. 
 
3. RESULTS AND DISCUSSION 
 
By electropolish of Al samples the height of rough-
ness decrease from 250 nm to 3 nm. AFM image of the 
surface before and after of electropolish was shown in 
Fig. 1. The mirror–like surface is suitable to fabricate 
of highly ordered porous anodic aluminum oxide. 
 
 
 
Fig. 1 – AFM of Surface of the Al foil (a) before and (b) after 
the electropolish 
 
To improve the ordering of the surface side of the 
anodic porous alumina, two-step anodization is effec-
tively adopted After the removal of the oxide, an array 
of highly ordered dimples was formed on the Al, and 
these dimples can act as initiation sites for the hole 
development in the second anodization. The AFM view 
of surface for anodization with acid sulfuric after re-
move the oxide layer in first anodization was shown in 
Fig. 2. SEM image of AAO template after second ano-
dization in sulfuric was seen in Fig. 3. 
 
 
 
Fig. 2 – SEM AFM image of Surface of the AAO after remove 
the oxide layer in first anodization in sulfuric acid 
 
 
Fig. 3 – SEM image of surface of AAO after 2nd anodization in 
sulfuric acid 
 
SEM image of synthesized nanowires with diameter 
of 20 and 35 nm are shown in Fig. 4.  
 
 
 
Fig. 4 – a) SEM image of nanowires with 35 nm diameters 
and 2.1 mm length and (b) with 20 nm diameter and 2.5 mm  
length 
 
The coercivity and squareness of the samples are 
showed in Fig. 5. It can be seen coercivity of nanowires 
with 20 and 35 nm diameter by addition of impurities 
zinc in the electrolyte of electro deposition. The coer-
cively decreases because Zinc atoms replaces to cobalt 
atoms and reduce magnetic properties. The regular 
increase coercivity with decreasing diameter was 
shown with Comparison two curves with 20 and 35 nm.  
 
0.00 0.05 0.10 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800
H
c
(O
e
)
Concentration of Zinc (M)
 sulfuric(diameter:20nm)
 oxalic(diameter:35)
 
 
Fig. 5 – Coercivity of nanowires with diameters of 20 and 35 
nm 
 
Coersivity field of nanowires with diameters of 
20 nm and 35 nm when increase zinc in electrolyte of 
electro deposition, decrease from 1711 Oe to 260 Oe 
and from 1500 to 270 Oe respectively. The effect of an-
nealing temperature of samples with diameter of 20 
and 35 nm on coercivitiy was examined in Fig. 6. It is 
supposed the loss of tension in annealing process is the 
reasons to improve the coercivity. The most coersivity 
 THE EFFECT OF DIAMETER AND THERMAL TREATMENT… PROC. NAP 1, 04MFPN09 (2012) 
 
 
04MFPN09-3 
(Hc  2120 Oe) related to sample with 10 percentage 
(x  1) of zinc in electrodeposition electrolyte with di-
ameter of 20 nm. Fig. 7 is shown squareness of samples 
before and after the annealing. The most change in 
both diameters is related to the sample with x  5 after 
annealing in 575 C. 
 
0.00 0.05 0.10 0.15 0.20
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
H
c
 (
O
e
)
concentration of zinc (M)
 as prepared
 200
0
c
 300
0
c
 400
0
c
 450
0
c
 500
0
c
 550
0
c
 575
0
c
 
 
0.00 0.05 0.10 0.15 0.20
200
400
600
800
1000
1200
1400
1600
H
c
(O
e
)
concentration of zinc(M)
 as prepared
 200
0
 c
 300
0
 c
 400
0
 c
 450
0
 c
 500
0
 c
 550
0
 c
 575
0
 c
 
 
Fig. 6 – The coercivity of Co1-xZnx nanowires with diameter of 
(a)20 nm and (b) 35 nm as a function of percentage of Zn and 
annealing temperature  
 
4. CONCLUSIONS 
 
In this paper the nanowires of Co1-xZnx with 20 and 
35 nm fabricated by electrodeposition method and coer-
sivity field decrease by increasing of Zinc but annealing 
in 575 C causes the magnetic properties of nanowires 
clearly increase. The highest coercivity and squareness 
after annealing related to Co90Zn10 (Hc  2120 Oe) and 
Co95Zn5 (sq  1),respectively. 
 
0.00 0.05 0.10 0.15 0.20
0.74
0.76
0.78
0.80
0.82
0.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
M
r/
M
s
concentration of zinc(M)
 as prepared
  575
0
 c
 
 
0.00 0.05 0.10 0.15 0.20
0.5
0.6
0.7
0.8
0.9
1.0
M
r/
M
s
concentration of zinc (M)
 as prepared
 575
0
 c
 
 
Fig. 7 – Squareness of nanowires with (a) 20 nm and (b) 
35 nm diameter to concentration of zinc (M) before and after 
annealing in 575 C 
 
AKNOWLEDGEMENT 
 
The authors are grateful for the financial support 
from the Grant Research Councils of HUT and Univer-
sity of Kurdistan. 
 
 
 
 
REFERENCES 
 
1. L. Sun, P.C. Seatson, C.L. Chien, J. Magn. Magn. Mater. 
49, 79 (2005)  
2. Y. Zhou, C. Shen, H.  Li, Solid State Ionics 146, 81 (2002)  
3. J.P. Pauzauskie, P.D. Yang, Mater. Today 9, 36 (2006)  
4. D. Routkevitch, A. Tager, A. Haruyama, D. Almawlawi,  
D. Moskovits, IEEE Trans. Electron. Dev. 146, 1646 
(1996). 
5. W. Lee, C.A. Ross, U. Gosele, K. Nielsch, J. Appl. Phys. 2, 
978 (2006)  
6. Y. Ren, S.L. Li, J.B. Wang, X.H. Han, J. Magn. Magn. Ma-
ter. 321, 226 (2009)  
7. H. Masuda, K. Fukuda, Science 268,1466 (1994) 
8. A. Saedi, M. Ghorbani, Mater. Chem. Phys. 91, 417 (2005)  
 
(a) 
(b) 


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The Effect of Diameter and Thermal Treatment on Magnetic Properties of Co1-xZnx Alloy Nanowires

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