- Email: [email protected]
Temperature dependence of the magnetic hyperfine field of chemically prepared amorphous Fe-B alloy particles
Journal of Magnetism and Magnetic Materials 104-107 (1992) 167-169 North-Holland
Temperature dependence of the magnetic hyperfine field of chemically prepared amorphous Fe-B alloy particles Soren Linderoth Laboratory of Applied Physics, Technical Unicersity of Denmark, DK-2800 Lyngby, Denmark Amorphous alloy Fe I xBx alloy particles have been prepared by a chemical reduction method and the dependence on temperature of the magnetic hyperfine splitting of 57Fe studied in the temperature interval from 10 to about 650 K for samples containing 16, 21, and 26 at% B, respectively. The decrease of the hyperfine field with temperature is in accord with the Bloch T3/e-law with coefficients that depend on boron content in a manner very similar to that of melt-spun samples. The Curie temperatures have also been estimated, and they are close to those of films and ribbons prepared by more conventional methods. The results show that the intrinsic magnetic properties of the differently prepared alloys are very similar. A m o r p h o u s alloys can be prepared by a number of different techniques, e.g., by sputtering, melt-spinning, mechanical alloying, thermal decomposition and chemical reduction. It is interesting to study the properties of the different types of alloys and to compare their properties. In this paper we present M6ssbauer spectroscopy studies of amorphous F e - B alloy particles, prepared in aqueous solutions by a chemical reduction method, and we compare the magnetic properties with those of melt-spun and sputter-prepared samples. The F e - B alloy particles were prepared by the chemical reduction method described in a recent review paper [1]. Passivated F e - B alloy particles were studied by M6ssbauer spectroscopy as a function of temperature in the temperature range 10-650 K. The measurements below room temperature were performed with the sample attached to the cold-finger of a closed-cycle He cryostat. Measurements above room temperature were made on a self-supporting sample of compacted particles. The particles were mixed with BN in order to increase the thickness of the self-supporting sample without introducing serious saturation effects in the M6ssbauer spectrum. The sample was placed in a quartz oven with a flow of warm argon gas passing the sample. In either case the samples were studied by transmission M6ssbauer spectroscopy with a source of 57Co in rhodium. The magnetic hyperfine splitting was determined by least-squares fitting by six broad Lorentzian lines, or by measuring the splitting between lines 1 and 6 and between lines 2 and 5 in the M6ssbauer spectra. Three amorphous F e - B alloy particle samples with boron contents of 16, 21 and 26 at%, respectively, were studied as a function of measuring temperature. The decrease of the magnetic hyperfine field with increasing measuring temperature is seen in fig. 1. The hyperfine field has at 600 K decreased to about half of its value at 10 K. Measuring at temperatures above approximately 650 K resulted in some crystallization of the samples and those data are therefore not included
35f a - FeB4 B 16 !
2150 2 5 3 0 [ ' ' ' ' * '
|j
el I i
J o
10 v '10
a- Fe79 B21 o
==
i
! i
| J i |
i I I
fO~ (U 0 - =E 30
a - F e 7 4 B26
25
20 15
i i i i i
'
10
O0
200 400 600 T e m p e r a t u r e (K)
t
t
800
Fig. 1. The magnetic hyperfine field a a function of temperature, for three samples of amorphous Fe~ xBx alloy particles prepared by the chemical reduction method.
in fig. 1. By extrapolating the magnetic hyperfine field to zero value the Curie temperature of the alloys can be estimated, and they were found to be (650_+ 30), (700 _+ 20) and (750 _+ 30) K, respectively for the amorphous Fes4B16, Fe79B21 and Fe74B26 alloy particles.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
168 900
S. Linderoth / Temperature dependence of B h f. of Fe-B alloy particles I
xx +
JAmorphous Fe-B -- 800,,e" 700
I
E
.
600 I
5OO x
i
400 ~ 0
10
20
B (at
~/
30
40
O0
Fig. 2. The Curie temperature of amorphous Fet_ ~B~ alloys prepared by the chemical reduction method (squares), by melt-spinning (circles [3] and crosses [5]), and by sputtering (triangles [4]). The transition temperatures have in the present work and in ref. [3] been estimated from M6ssbauer spectroscopy measurements and in refs. [4,5] from magnetization measurements.
35
,
30 ~ . ~ "
•
a'Fe84
T h e s e values are plotted in fig. 2. Shown arc also the transition t e m p e r a t u r e fl)r Fe62B3s particles, as previously e s t i m a t e d from m a g n e t i z a t i o n m e a s u r e m e n t s [2], as well as Curie t e m p e r a t u r e s for a m o r p h o u s Fe I .t B, ribbons and films p r e p a r e d by melt-spinning and sputtering, respectively, as estimated from e i t h e r M 6 s s b a u e r spectroscopy [3] or s a t u r a t i o n m a g n e t i z a t i o n m e a s u r e m e n t s [4,5]. Considering the very different p r e p a r a t i o n m e t h o d s and form of the alloy samples it may be surprising to note the a g r e e m e n t b e t w e e n the values for the Curie t e m p e r a t u r e s for the different types of samples. Not just the t r e n d is similar, but also the absolute values are the same within uncertainties. F e r r o m a g n e t i c alloys, b o t h crystalline and amorphous, have b e e n found to follow the Bloch T~/2-1aw
[3,~,]: Bh,(r)
= Bh
(l)
(O)(l -
T h e T 3 / Z - d e p e n d e n c e has b e e n observed in both M 6 s s b a u e r spectroscopy and m a g n e t i z a t i o n m e a s u r e m e n t s [3]. In fig. 3 Bhl- is plottet as a function of T 3/2 for the t h r e e particle samples and a linear d e p e n d e n c e is seen up to about 500 K. T h e slope of the fitted straight lines in fig. 3 are plotted in fig. 4 t o g e t h e r with b-values found in the literature for melt-spun samples.
B16 40 "
I 20
c,l
15 "o
30
~
10 ! i
.
.
.
~ 20
. . . . . a - F e 7 9 B21
..Q
10 r
~
25 t rU
+---
0
20
~
0.6
4
15,
C 1 0
~
r
-
i Amorphous Fe-B
-
c~
a-Fe74B26
0,5 i
o4 i
0.3 ~
[
15
lO0i
J
5.000
10.000
i 15.000
T 3/2
Fig. 3. The magnetic hyperfine field shown as a function of T 3/2, for three amorphous Fel_xB x alloy particle samples. The straight lines are fits to points below about 500 K.
0.2
10
15
20 B iat ~a)
25
30
Fig. 4. The upper part of the figure shows the b-values extracted from the fittings shown in fig. 3 to eq. (l), while the lower figure shows the b~/2-values deduced from eq. (2). The squared figure points are for samples studies in the present work, and the circles are for melt-spun samples [3].
S. Linderoth / Temperaturedependenceof Bhf of Fe-B alloyparticles
169
The dependence of the slope on the boron content for the two different types of samples is seen to be quite similar. Equation (1) may also be written as:
techniques, and it turns out that, despite the very different preparation methods, the intrinsic magnetic properties, such as the Curie temperature and the temperature dependence of the magnetic hyperfine field, are very similar.
Bhf=Bhe(O) 1 - b 3 / 2 ~ ]
References
],
(2)
and by inserting the values for T¢ and b from figs. 2 and 4 b3/2 can be calculated. The values are shown in the lower part of fig. 4. It is clear that with the nice accordance between the b-values and T¢-values for the two types of alloys this will also be the case for the b3/2-values. In summary, the temperature dependence of the magnetic hyperfine field of amorphous Fe l_xBx alloy particles have been studied by M6ssbauer spectroscopy in the temperature range between 10 and about 650 K. The results have been compared with measurements of similar alloys prepared by sputtering and liquid-quench
[1] S. Linderoth and S. Morup, J. Appl. Phys. 69 (1991) 5256. [2] S. Linderoth, S. Morup, A. Meagher, J. Earsen, M.D. Bentzon, B.S. Clausen, C.J.W. Koch, S. Wells and S.W. Charles, J. Magn. Magn. Mater. 81 (1989) 138. [3] C.L. Chien, D. Musser, E.M. Gyorgy, R.C. Sherwood, H.S. Chen, F.E. Luborsky and J.L. Walter, Phys. Rev. B 20 (1979) 283. [4] F. Kanamura, S. Miyazaki, M. Shimada, M. Koizumi, K. Oda and Y. Mimu, J. Solid State Chem. 49 (1983) 1. [5] T. Nakajima, E. Kita and H. Ino, J. Mater. Sci. 23 (1988) 1279. [6] N.W. Ashcroft and N.M. Mermin, Solid State Physics, (Holt, Rinehart and Winston, New York, 1979).
Temperature dependence of the magnetic hyperfine field of chemically prepared amorphous Fe-B alloy particles Soren Linderoth Laboratory of Applied Physics, Technical Unicersity of Denmark, DK-2800 Lyngby, Denmark Amorphous alloy Fe I xBx alloy particles have been prepared by a chemical reduction method and the dependence on temperature of the magnetic hyperfine splitting of 57Fe studied in the temperature interval from 10 to about 650 K for samples containing 16, 21, and 26 at% B, respectively. The decrease of the hyperfine field with temperature is in accord with the Bloch T3/e-law with coefficients that depend on boron content in a manner very similar to that of melt-spun samples. The Curie temperatures have also been estimated, and they are close to those of films and ribbons prepared by more conventional methods. The results show that the intrinsic magnetic properties of the differently prepared alloys are very similar. A m o r p h o u s alloys can be prepared by a number of different techniques, e.g., by sputtering, melt-spinning, mechanical alloying, thermal decomposition and chemical reduction. It is interesting to study the properties of the different types of alloys and to compare their properties. In this paper we present M6ssbauer spectroscopy studies of amorphous F e - B alloy particles, prepared in aqueous solutions by a chemical reduction method, and we compare the magnetic properties with those of melt-spun and sputter-prepared samples. The F e - B alloy particles were prepared by the chemical reduction method described in a recent review paper [1]. Passivated F e - B alloy particles were studied by M6ssbauer spectroscopy as a function of temperature in the temperature range 10-650 K. The measurements below room temperature were performed with the sample attached to the cold-finger of a closed-cycle He cryostat. Measurements above room temperature were made on a self-supporting sample of compacted particles. The particles were mixed with BN in order to increase the thickness of the self-supporting sample without introducing serious saturation effects in the M6ssbauer spectrum. The sample was placed in a quartz oven with a flow of warm argon gas passing the sample. In either case the samples were studied by transmission M6ssbauer spectroscopy with a source of 57Co in rhodium. The magnetic hyperfine splitting was determined by least-squares fitting by six broad Lorentzian lines, or by measuring the splitting between lines 1 and 6 and between lines 2 and 5 in the M6ssbauer spectra. Three amorphous F e - B alloy particle samples with boron contents of 16, 21 and 26 at%, respectively, were studied as a function of measuring temperature. The decrease of the magnetic hyperfine field with increasing measuring temperature is seen in fig. 1. The hyperfine field has at 600 K decreased to about half of its value at 10 K. Measuring at temperatures above approximately 650 K resulted in some crystallization of the samples and those data are therefore not included
35f a - FeB4 B 16 !
2150 2 5 3 0 [ ' ' ' ' * '
|j
el I i
J o
10 v '10
a- Fe79 B21 o
==
i
! i
| J i |
i I I
fO~ (U 0 - =E 30
a - F e 7 4 B26
25
20 15
i i i i i
'
10
O0
200 400 600 T e m p e r a t u r e (K)
t
t
800
Fig. 1. The magnetic hyperfine field a a function of temperature, for three samples of amorphous Fe~ xBx alloy particles prepared by the chemical reduction method.
in fig. 1. By extrapolating the magnetic hyperfine field to zero value the Curie temperature of the alloys can be estimated, and they were found to be (650_+ 30), (700 _+ 20) and (750 _+ 30) K, respectively for the amorphous Fes4B16, Fe79B21 and Fe74B26 alloy particles.
0312-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
168 900
S. Linderoth / Temperature dependence of B h f. of Fe-B alloy particles I
xx +
JAmorphous Fe-B -- 800,,e" 700
I
E
.
600 I
5OO x
i
400 ~ 0
10
20
B (at
~/
30
40
O0
Fig. 2. The Curie temperature of amorphous Fet_ ~B~ alloys prepared by the chemical reduction method (squares), by melt-spinning (circles [3] and crosses [5]), and by sputtering (triangles [4]). The transition temperatures have in the present work and in ref. [3] been estimated from M6ssbauer spectroscopy measurements and in refs. [4,5] from magnetization measurements.
35
,
30 ~ . ~ "
•
a'Fe84
T h e s e values are plotted in fig. 2. Shown arc also the transition t e m p e r a t u r e fl)r Fe62B3s particles, as previously e s t i m a t e d from m a g n e t i z a t i o n m e a s u r e m e n t s [2], as well as Curie t e m p e r a t u r e s for a m o r p h o u s Fe I .t B, ribbons and films p r e p a r e d by melt-spinning and sputtering, respectively, as estimated from e i t h e r M 6 s s b a u e r spectroscopy [3] or s a t u r a t i o n m a g n e t i z a t i o n m e a s u r e m e n t s [4,5]. Considering the very different p r e p a r a t i o n m e t h o d s and form of the alloy samples it may be surprising to note the a g r e e m e n t b e t w e e n the values for the Curie t e m p e r a t u r e s for the different types of samples. Not just the t r e n d is similar, but also the absolute values are the same within uncertainties. F e r r o m a g n e t i c alloys, b o t h crystalline and amorphous, have b e e n found to follow the Bloch T~/2-1aw
[3,~,]: Bh,(r)
= Bh
(l)
(O)(l -
T h e T 3 / Z - d e p e n d e n c e has b e e n observed in both M 6 s s b a u e r spectroscopy and m a g n e t i z a t i o n m e a s u r e m e n t s [3]. In fig. 3 Bhl- is plottet as a function of T 3/2 for the t h r e e particle samples and a linear d e p e n d e n c e is seen up to about 500 K. T h e slope of the fitted straight lines in fig. 3 are plotted in fig. 4 t o g e t h e r with b-values found in the literature for melt-spun samples.
B16 40 "
I 20
c,l
15 "o
30
~
10 ! i
.
.
.
~ 20
. . . . . a - F e 7 9 B21
..Q
10 r
~
25 t rU
+---
0
20
~
0.6
4
15,
C 1 0
~
r
-
i Amorphous Fe-B
-
c~
a-Fe74B26
0,5 i
o4 i
0.3 ~
[
15
lO0i
J
5.000
10.000
i 15.000
T 3/2
Fig. 3. The magnetic hyperfine field shown as a function of T 3/2, for three amorphous Fel_xB x alloy particle samples. The straight lines are fits to points below about 500 K.
0.2
10
15
20 B iat ~a)
25
30
Fig. 4. The upper part of the figure shows the b-values extracted from the fittings shown in fig. 3 to eq. (l), while the lower figure shows the b~/2-values deduced from eq. (2). The squared figure points are for samples studies in the present work, and the circles are for melt-spun samples [3].
S. Linderoth / Temperaturedependenceof Bhf of Fe-B alloyparticles
169
The dependence of the slope on the boron content for the two different types of samples is seen to be quite similar. Equation (1) may also be written as:
techniques, and it turns out that, despite the very different preparation methods, the intrinsic magnetic properties, such as the Curie temperature and the temperature dependence of the magnetic hyperfine field, are very similar.
Bhf=Bhe(O) 1 - b 3 / 2 ~ ]
References
],
(2)
and by inserting the values for T¢ and b from figs. 2 and 4 b3/2 can be calculated. The values are shown in the lower part of fig. 4. It is clear that with the nice accordance between the b-values and T¢-values for the two types of alloys this will also be the case for the b3/2-values. In summary, the temperature dependence of the magnetic hyperfine field of amorphous Fe l_xBx alloy particles have been studied by M6ssbauer spectroscopy in the temperature range between 10 and about 650 K. The results have been compared with measurements of similar alloys prepared by sputtering and liquid-quench
[1] S. Linderoth and S. Morup, J. Appl. Phys. 69 (1991) 5256. [2] S. Linderoth, S. Morup, A. Meagher, J. Earsen, M.D. Bentzon, B.S. Clausen, C.J.W. Koch, S. Wells and S.W. Charles, J. Magn. Magn. Mater. 81 (1989) 138. [3] C.L. Chien, D. Musser, E.M. Gyorgy, R.C. Sherwood, H.S. Chen, F.E. Luborsky and J.L. Walter, Phys. Rev. B 20 (1979) 283. [4] F. Kanamura, S. Miyazaki, M. Shimada, M. Koizumi, K. Oda and Y. Mimu, J. Solid State Chem. 49 (1983) 1. [5] T. Nakajima, E. Kita and H. Ino, J. Mater. Sci. 23 (1988) 1279. [6] N.W. Ashcroft and N.M. Mermin, Solid State Physics, (Holt, Rinehart and Winston, New York, 1979).