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Magnetic and structural properties of electrodeposited CoNiP amorphous ribbons
Journal of Magnetism and Magnetic Materials 177 181 (1998) 119 120
J H Journalof magnetism and magnetic ~ l ~ materials
N
ELSEVIER
Magnetic and structural properties of electrodeposited Co-Ni-P amorphous ribbons G. Rivero, M. Multigner*, J.M. Garcia, P. Crespo, A. Hernando Instituto de Magnetismo Aplicado, Universidad Complutense de Madrid- Instituto de Ciencia de Materiales de Madrid (CSIC), P. O. Box 155, 28230 Las Rozas, Madrid, Spain
Abstract Series of C o - N i - P amorphous ribbons have been prepared by electrodeposition for a wide range of composition. The magnetic behavior of the material depends strongly on the Co/Ni ratio, ranging from paramagnetic to ferromagnetic as the Co content increases. The magnetic moment of the samples increases linearly with the Co content, and the extrapolation for 100 % Co content is very close to that of crystalline Co. Although the X-ray diffraction patterns indicate that the material is amorphous, the observed magnetic behavior suggests that the system is composed by nanocrystalline Co particles embedded in an amorphous Ni P matrix. © 1998 Elsevier Science B.V. All rights reserved.. Keywords." Amorphous ribbons; Electrodeposition; Nanoparticles; Superparamagnetism
Amorphous C o - N i - P ribbons have been prepared by electrodeposition on a Cu substrate from an acid bath at 70°C. The bath composition is shown in Table 1. The electrolytic current density was varied between 50 and 600 mA/cm / and film thickness was around 20 gm. The Co content ranges from 25 to 65 at% while Ni content varies from 50 to 18 at% as shown in Fig. 1. For all samples studied in the as-deposited state, X-ray diffraction patterns only show a typical amorphous halo which is placed on the angle corresponding to principal HCP-Co and FCC-Co diffraction peaks, as indicated in Fig. 2. On the other hand, TEM analysis reveals that the samples consist of an amorphous matrix with inclusions of nanocrystallites, whose size and concentration vary with Co content. Due to the absence of diffraction peaks, the size of the crystallites observed by TEM should be lower than 20 nm. TEM analysis of the as-deposited samples shows electron diffraction patterns corresponding to a polycrystalline material. From the measurement of the radius, the rings can be indexed on the basis of the hexagonal cell characteristic of HCP-Co (Fig. 3). Compositional analysis is in good agreement with magnetic measurements: the average magnetic moment
of the samples increases linearly with Co atomic percentage as indicated in Fig. 4. A rough extrapolation for 100% Co content gives rise to a value very close to that of crystalline Co. Table 1 Electrolytic bath composition Chemical products
Concentration
H3PO3 (30%) H3PO4 (85%) NiCO3 NiC12 + 6H20 COCO3 COC12 + 6H20
133 cm3/1 35 cm3/1 23 g/1 110 g/1 10 g/1 45 g/1
70 60 50 '~
40 30 20 10
,
,
100
*Corresponding author. Fax: + 34 1 630 1625; e-mail: [email protected]. 0304-8853/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 6 6 4 - 1
.
,
200
.
,
300
.
,
400
.
~
500
.
,
600
J (mA/cm 2)
Fig. 1. Film composition versus current density.
120
G. Rivero et al. / Journal of Magnetism and Magnetic Materials" 177-181 (1998) 119-120 78..
76~
.... h c p C o
74• 7270686630
40
50
60
64
70
50
100
150
2e(°)
200
250
300
T (K)
Fig. 2. X-ray diffraction pattern of the as-deposited Co36Ni,, aPz 3 sample. The lines indicate the position of principal diffraction peaks of HCP- and FCC-Co.
Fig. 5. Specific magnetic moment of the as-deposited Co56Ni2~,P20 sample versus temperature. Measurement was made in a SQUID magnetometer under an applied magnetic field of 50 kOe.
,
,
,
.
,
.
,
,
,
.
,
•
,
8
6
50
100
•
ZFC
•
FC
150
200
250
300
T(K)
Fig. 6. Specific
magnetic
moment
of
the
as-obtained
Co36Ni41P23 sample versus temperature under an applied field of 20 Oe after zero-field cooling (A, ZFC) and field cooling (T, FC). Blocking temperature is about 20 K. Fig. 3. Electron diffraction pattern of the as-deposited C036Ni41P23 sample, rings corresponding to the (h 0 0) planes. percentage above 45% (Fig. 5). Below this value, the dependence of magnetization with temperature, zerofield cooled (ZFC) and field cooled (FC), shows a superparamagnetic behavior, with a blocking temperature that varies between 10 and 20 K, depending on the composition (Fig. 6). Using the value of the anisotropy constant reported by Chikazumi [2], the critical size of crystallites is estimated [-3] to be between 10 and 20 nm, which agrees with the results obtained by X-ray diffraction and TEM.
100
6o
v 40
20
0
, 20
•
, 30
•
,
.
40
, 50
,
, 60
,
, 70
% at. Co
Fig. 4. Specific magnetic moment of the samples versus Co atomic percentage at temperature of 5 K, under an applied magnetic field of 50 kOe. These results suggest that the samples consist of a non-magnetic amorphous matrix, mainly composed of amorphous NiP, and HCP- or FCC-Co nanocrystallites, whose n u m b e r and size depend on Co content. As is well known, amorphous NiP is non-magnetic for P content above 15 at% [1]. Furthermore, measurements of magnetic moment versus temperature indicate that the samples exhibit ferromagnetic behavior for Co atomic
M. Multigner acknowledges partial support from FISS (no 95/1233) and J.M. Garcia acknowledges Volkswagen Audi-CSIC for his grant. The authors are indebted to Prof. J. Gonz/dez Calbet and M. Vallet-Regi for help in structural characterization, and to Dr. A. GarciaEscorial for composition measurements.
References
[1] D. Pan, D. Turnbull, J. Appl. Phys. 45 (1974) 1406. [2] S. Chikazumi, Physics of Magnetism, Krieger, Malabar, 1978, p. 261. /-3] B.D. Cullity, Introduction to Magnetic Materials, Addison-Wesley, Reading, MA, 1972, p. 413.
J H Journalof magnetism and magnetic ~ l ~ materials
N
ELSEVIER
Magnetic and structural properties of electrodeposited Co-Ni-P amorphous ribbons G. Rivero, M. Multigner*, J.M. Garcia, P. Crespo, A. Hernando Instituto de Magnetismo Aplicado, Universidad Complutense de Madrid- Instituto de Ciencia de Materiales de Madrid (CSIC), P. O. Box 155, 28230 Las Rozas, Madrid, Spain
Abstract Series of C o - N i - P amorphous ribbons have been prepared by electrodeposition for a wide range of composition. The magnetic behavior of the material depends strongly on the Co/Ni ratio, ranging from paramagnetic to ferromagnetic as the Co content increases. The magnetic moment of the samples increases linearly with the Co content, and the extrapolation for 100 % Co content is very close to that of crystalline Co. Although the X-ray diffraction patterns indicate that the material is amorphous, the observed magnetic behavior suggests that the system is composed by nanocrystalline Co particles embedded in an amorphous Ni P matrix. © 1998 Elsevier Science B.V. All rights reserved.. Keywords." Amorphous ribbons; Electrodeposition; Nanoparticles; Superparamagnetism
Amorphous C o - N i - P ribbons have been prepared by electrodeposition on a Cu substrate from an acid bath at 70°C. The bath composition is shown in Table 1. The electrolytic current density was varied between 50 and 600 mA/cm / and film thickness was around 20 gm. The Co content ranges from 25 to 65 at% while Ni content varies from 50 to 18 at% as shown in Fig. 1. For all samples studied in the as-deposited state, X-ray diffraction patterns only show a typical amorphous halo which is placed on the angle corresponding to principal HCP-Co and FCC-Co diffraction peaks, as indicated in Fig. 2. On the other hand, TEM analysis reveals that the samples consist of an amorphous matrix with inclusions of nanocrystallites, whose size and concentration vary with Co content. Due to the absence of diffraction peaks, the size of the crystallites observed by TEM should be lower than 20 nm. TEM analysis of the as-deposited samples shows electron diffraction patterns corresponding to a polycrystalline material. From the measurement of the radius, the rings can be indexed on the basis of the hexagonal cell characteristic of HCP-Co (Fig. 3). Compositional analysis is in good agreement with magnetic measurements: the average magnetic moment
of the samples increases linearly with Co atomic percentage as indicated in Fig. 4. A rough extrapolation for 100% Co content gives rise to a value very close to that of crystalline Co. Table 1 Electrolytic bath composition Chemical products
Concentration
H3PO3 (30%) H3PO4 (85%) NiCO3 NiC12 + 6H20 COCO3 COC12 + 6H20
133 cm3/1 35 cm3/1 23 g/1 110 g/1 10 g/1 45 g/1
70 60 50 '~
40 30 20 10
,
,
100
*Corresponding author. Fax: + 34 1 630 1625; e-mail: [email protected]. 0304-8853/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved PII S 0 3 0 4 - 8 8 5 3 ( 9 7 ) 0 0 6 6 4 - 1
.
,
200
.
,
300
.
,
400
.
~
500
.
,
600
J (mA/cm 2)
Fig. 1. Film composition versus current density.
120
G. Rivero et al. / Journal of Magnetism and Magnetic Materials" 177-181 (1998) 119-120 78..
76~
.... h c p C o
74• 7270686630
40
50
60
64
70
50
100
150
2e(°)
200
250
300
T (K)
Fig. 2. X-ray diffraction pattern of the as-deposited Co36Ni,, aPz 3 sample. The lines indicate the position of principal diffraction peaks of HCP- and FCC-Co.
Fig. 5. Specific magnetic moment of the as-deposited Co56Ni2~,P20 sample versus temperature. Measurement was made in a SQUID magnetometer under an applied magnetic field of 50 kOe.
,
,
,
.
,
.
,
,
,
.
,
•
,
8
6
50
100
•
ZFC
•
FC
150
200
250
300
T(K)
Fig. 6. Specific
magnetic
moment
of
the
as-obtained
Co36Ni41P23 sample versus temperature under an applied field of 20 Oe after zero-field cooling (A, ZFC) and field cooling (T, FC). Blocking temperature is about 20 K. Fig. 3. Electron diffraction pattern of the as-deposited C036Ni41P23 sample, rings corresponding to the (h 0 0) planes. percentage above 45% (Fig. 5). Below this value, the dependence of magnetization with temperature, zerofield cooled (ZFC) and field cooled (FC), shows a superparamagnetic behavior, with a blocking temperature that varies between 10 and 20 K, depending on the composition (Fig. 6). Using the value of the anisotropy constant reported by Chikazumi [2], the critical size of crystallites is estimated [-3] to be between 10 and 20 nm, which agrees with the results obtained by X-ray diffraction and TEM.
100
6o
v 40
20
0
, 20
•
, 30
•
,
.
40
, 50
,
, 60
,
, 70
% at. Co
Fig. 4. Specific magnetic moment of the samples versus Co atomic percentage at temperature of 5 K, under an applied magnetic field of 50 kOe. These results suggest that the samples consist of a non-magnetic amorphous matrix, mainly composed of amorphous NiP, and HCP- or FCC-Co nanocrystallites, whose n u m b e r and size depend on Co content. As is well known, amorphous NiP is non-magnetic for P content above 15 at% [1]. Furthermore, measurements of magnetic moment versus temperature indicate that the samples exhibit ferromagnetic behavior for Co atomic
M. Multigner acknowledges partial support from FISS (no 95/1233) and J.M. Garcia acknowledges Volkswagen Audi-CSIC for his grant. The authors are indebted to Prof. J. Gonz/dez Calbet and M. Vallet-Regi for help in structural characterization, and to Dr. A. GarciaEscorial for composition measurements.
References
[1] D. Pan, D. Turnbull, J. Appl. Phys. 45 (1974) 1406. [2] S. Chikazumi, Physics of Magnetism, Krieger, Malabar, 1978, p. 261. /-3] B.D. Cullity, Introduction to Magnetic Materials, Addison-Wesley, Reading, MA, 1972, p. 413.