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Mössbauer study of the spin orientation along the length of the amorphous FeCrSiB ribbon
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Solid State Communicalims,Vol. 82, No. 5, pp. 321-324, 1992. Printed in Great Britain.
MOSSBAUER ffI'ODYOFTHE SPIN ORIENTATION ALONG THE LENGTH OF THE AMORPHOUS FeCRSiBRIBBON Marcel Miglierini* and Jozef Sitek
Department of Nuclear Physics and Technology, Slovak Technical University, Mlynsk6 dolina, C$-812 19 Bratislava, Czechoslovakia (Received 29 January 1992 and in revised form 2 Mm'ch 1992 by A. Okiji)
Differences in the magnetic structures between the initial and the final parts of the amorphous FesoCr2Si4B 14 ribbon are detected by M6ssbaner spectroscopy. Using the magic angle method an increase of the in-plane anisotropy in the final part of the ribbon is revealed. The observed deviations in spin orientation along the ribbon length are discussed to be due to changed conditions during the preparation of the samples.
magnetic structures between the initial and the final parts of the amorphous Feg0Cr2Si4BI4 ribbon from the point of view of M6ssbauer spectroscopy.
1. INTRODUCTION Applications of metallic glasses need a thorough knowledge of their physical properties. An investigation of the preparation conditions seems to be also helpful. In case of the melt spinning technique, an influence of varying production parameters on properties and structure of amorphous alloys was studied using a number of methods. TM Among them the MOssbauer spectroscopy plays an important role which is unmatched by any other method.2 Of the same importance is an investigation of the changes in preparation conditions during one technological cycle. They are possible sources of inhomogeneous as-cast anisotropy due to, e.g., geometrical aspects and/or deviations in the heat transfer during the solidification process. Domain patterns and magnetic properties were studied by Draganovsk~l et al. 5 on amorphous samples taken from different parts of as-cast ribbons. The authors 5 reported changes in domain structures influenced by local stresses within the ribbon which are induced by thermal gradients during rapid quenching. In this letter we deal with differences in *)
Present address: Department of Material Physics, Osaka University, Toyonaka, Osaka 560, Japan.
2. EXPERIMENTAL DETAILS The ribbons of amorphous Fes0Cr2Si4B 14 (30 mm wide and about 30 ttm thick) were produced by a planar flow casting method at the Institute of Physics, Slovak Academy of Sciences in Bratislava. The samples were cut from the initial and the final parts of the amorphous ribbon each one with the total area of about 1.5 x 1.5 cm2. The total length of the ribbon produced from one batch was about 200 m and the terms "initial" and "final" refer to the parts of the ribbon taken approximately 10 m from the respective ends. A conventional constant acceleration M6ssbauer spectrometer with a 57Co(Rh) source was used in transmission geometry. Special attention was paid to the sample holder to avoid additional stresses. The M6ssbaner spectra were fitted by means of the NORMOS DIST program 6 to the distributions of hyperfine magnetic fields using 25 subsextets. Asymmetries in the spectral lines observed were covered by introducing linear correlations between the electric quadrupole interaction and the isomer shift, and between 321
322
MOSSBAUER STUDY OF THE SPIN ORIENTATION
the hyperfine magnetic splitting and the isomer shift. A linewidth of 0.26 mm/s, equal to the intrinsic linewidth of the spectrometer used, was assumed for all subspectra. The parameters obtained from the fit comprise along with the values of the hyperfine magnetic field, quadrupole shift, isomer shift and correlation parameters also the relative ratio of the M0ssbauer lines which was of the same value for all subsextets.
Vol~ 82, 1~. 5
z
A
5'/I
B
3. RESULTS AND DISCUSSION
:-y
Room temperature MOssbauer spectra of the FesoCr2Si4BI4 metallic glass in Fig.1 exhibit familiar six-line Zeeman-split patterns. Such broad and overlapped lines cause, however, some uncertainties in the determination of the line intensities (areas). This disadvantage can be minimized by a magic angle methodT, 8 which is able to give texture-free spectra 9 and, hence, accurate values of the hyperfine parameters can be determined. I0 Thus, the M0ssbauer spectra have been taken in three configurations as shown in Fig.2. Greneche and Varret 9 demonstrated that such arrangements are sufficient to calculate the spin populations Nx,
z
Fig.2. Orientations of the radiation propagation with respect to the plane of the amorphous ribbon.
Ny, Nz along the principal axes of the minimum texture: Nz = < cos2(~ >^ 2
I
.
.
.
.
.
I
.
.
.
I
.
.
.
.
I
.
.
.
.
I
1.00
Ny-Nx = ~(< COS2q~ >B-< COS2@R>C)
(l) (2)
where OR is the angle between the radiation direction and the nuclear quantization axis, and the indexes A, B and C denote the particular configurations as shown in Fig.2. The angle OR can be determined by measuring the relative line intensities in the MOssbauer spectra. For 57Fe experiments, the line ratios are given as:
0.95 1.00
i
g o.95 1.00
It:I2:I3:I4:I5:I6 = 3:b :l:l:b :3,
(3)
where 4 . sin2@R b = 1 + cos2OR
0.90 .
-10
.
.
.
t
-5
.
.
.
•
.
.
.
.
0
I
5
.
.
.
.
(4)
Ii
10
vetoca,/ (nm~s) Fig.1. MOssbauer spectra taken from the final part of the amorphous FesoCr2Si4Bl4 ribbon at room temperature in configurations A, B and C (see Fig.2).
is one of the fitted variables in the spectrum analysis. The parameter b oan vary between the values /7 = 0 which corresponds to OR = 0 ° and implies a parallel orientation of the spins with respect to the radiation direction, and b = 4 for OR = 90° when the spins are perpendicular to the T-rays. Examples of the M6ssbauer spectra
Vol. 82, No. 5
323
MOSSBAUBR STUDY OF THE SPIN ORIENTATION
Table 1 M~ssbauer and magnetic texture analysis of FeaoCrzSicBl4 metallic glass. The figure enclosed in brackets shows the error in the last digit. part of the
OH
OR"
ribbon
(T)
(T)
(deg)
Nx
Ny
Nz
m~>c
initial
21.81(4) 4.30(5)
70.8(5)
0.426
0.466
0.108
0.647
final
21.80(3) 4.35(4)
74.9(47
0.421
0.511
0.068
0.620
a) OR-values derived fromA .
recorded from the final part of the amorphous FesoCr2Si4B14 ribbon are depicted in Fig.1 and all the results are summarized in table 1. The average value, < H >, as well as the standard deviation, OH, of the hyperfine field distribution remained practically the same for the respective parts of the ribbon. The change in the angle OR, however, indicates a tendency Of magnetic moments to turn into the plane of the ribbon in its final part. This is also supported by the magnetic texture components - - namely by the out-of-plane spin population Nz. From the decrease of Nz it can be concluded that the in-plane anisotropy of the final part increases. 11 Parameters Nx and are assigned to the spin populations in the x-y plane, i.e. in the plane of the ribbon. Although there is practically no change in Nx, an increase in Ny implies that the in-plane anisotropy is rising toward the final part of the ribbon. The last column in table 1 gives a convenient check for testing the quality of the method. 9 The observed departures from the expected value of 2/3 are similar to those reported by other authors 9.12 and they might be due to a divergence of the 3' beam.9 To interpret the observed changes in the magnetic structure, deviations in the heat transfer during the quenching as well as geometrical aspects should be taken into account. The in-plane anisotropy can be ascribed to both quenching conditions and magnetostrictive properties 12 which influence the magnetic texture and the geometrical shape via the inhomogeneous solidification process, surface crystallizationll and local stresses within the ribbon. 5 As a consequence, the shape anisotropy of the specimen is affected and most of the magnetic moments are aligned parallel to the ribbon plane. The above mentioned parameters govern the magnetic structure of the initial
part of the ribbon,5 i.e., at the beginning of the preparation. However, the situation is different in the final part of the ribbon, i.e., toward the end of the technological cycle. Here, the decreased value of the out-of-plane spin population Nz together with a tendency of the net magnetic moment to turn closer to the ribbon plane, as detected by the MOssbauer effect experiments (see table 1), suggests that variations in the above mentioned parameters during the preparation of the sample are responsible for the changes observed. This result is in agreement with the implications from the magnetic measurements reported by Draganovsk~ et al. 5 who proposed an explanation of the differences between the initial and the final parts of the ribbon based on the directional atomic pair ordering.
4. CONCLUSIONS MOssbauer spectroscopy is a useful tool for studying magnetic structure on a nuclear level. The use of the magic angle method and the magnetic texture analysis allowed us to reveal differences between the initial and the final parts of the amorphous F~oCr2Si4BI4 ribbon. The population of the out-of-plane oriented spins is falling down toward the final part of the ribbon giving rise to an increase in the in-plane anisotropy. Such behaviour is supposed to be due to deviations in the conditions during the production of metallic glasses by a spinning technique. Acknowledgements - We are indebted to Dr.P. Duhaj for supplying us with the amorphous ribbons. MM gratefully appreciates the warm hospitality of Osaka University during the completing of the manuscript.
324
MOSSBAUI~ STUDY OF THE SPIN ORIENTATION
1. H. J. Bauer, U. Gonser & H. G. Wagner, Hyperflne Interactions 27, 401 (1986). 2. U. Goaser, H. J. Bauer & H. G.Wagner, J.Magn.Magn.Mater. 70, 419 (1987). 3. T. Limbach & U. Gonser, J.Non.Crystal.Solids 106, 399 (1988). 4. Y. M. Yamam, N. G. Kinikoglu & N. Aydinbeyli, J.Mater.Sci.Lett. 9, 460 (1990). 5. H. Draganovskt, J. Sl4ma, P. Butvin & B. Butvinov& phys. stat. solidi (a) 115, 533 (1989). 6. R. A. Brand, NOltMO$ Programs, Internal Report, Angewandte Physik, Universi~t Duisburg (1987).
Vol. 82, No. 5
7. H. D. Pfannes & H. Fischer, Appl.Phys. 13, 317 (1977). 8. J. M. Greneche, M. Henry & F. V a t , t, Int. Conf. on the Applications of the M6ssbauer Effect, p.908, Indian National Science Academy, New Delhi (1982). 9. J. M. Greneche & F. Varret, J.Phys.C.: Solid State Phys. 15, 5333 (1982). 10. J. M. Gmneche & F. Varret, Solid State Commun. 54, 985 (1985). 11. P. Auric, J. M. Greneche, O. deBouvier & J. J. Rameau, J.Magn.Magn.Mater. 82, 243 (1989). 12. M. Henry, M. Bourrous, F. Varret & P. Founier, J.Mater.Sci. 19, 1000 (1984).
Solid State Communicalims,Vol. 82, No. 5, pp. 321-324, 1992. Printed in Great Britain.
MOSSBAUER ffI'ODYOFTHE SPIN ORIENTATION ALONG THE LENGTH OF THE AMORPHOUS FeCRSiBRIBBON Marcel Miglierini* and Jozef Sitek
Department of Nuclear Physics and Technology, Slovak Technical University, Mlynsk6 dolina, C$-812 19 Bratislava, Czechoslovakia (Received 29 January 1992 and in revised form 2 Mm'ch 1992 by A. Okiji)
Differences in the magnetic structures between the initial and the final parts of the amorphous FesoCr2Si4B 14 ribbon are detected by M6ssbaner spectroscopy. Using the magic angle method an increase of the in-plane anisotropy in the final part of the ribbon is revealed. The observed deviations in spin orientation along the ribbon length are discussed to be due to changed conditions during the preparation of the samples.
magnetic structures between the initial and the final parts of the amorphous Feg0Cr2Si4BI4 ribbon from the point of view of M6ssbauer spectroscopy.
1. INTRODUCTION Applications of metallic glasses need a thorough knowledge of their physical properties. An investigation of the preparation conditions seems to be also helpful. In case of the melt spinning technique, an influence of varying production parameters on properties and structure of amorphous alloys was studied using a number of methods. TM Among them the MOssbauer spectroscopy plays an important role which is unmatched by any other method.2 Of the same importance is an investigation of the changes in preparation conditions during one technological cycle. They are possible sources of inhomogeneous as-cast anisotropy due to, e.g., geometrical aspects and/or deviations in the heat transfer during the solidification process. Domain patterns and magnetic properties were studied by Draganovsk~l et al. 5 on amorphous samples taken from different parts of as-cast ribbons. The authors 5 reported changes in domain structures influenced by local stresses within the ribbon which are induced by thermal gradients during rapid quenching. In this letter we deal with differences in *)
Present address: Department of Material Physics, Osaka University, Toyonaka, Osaka 560, Japan.
2. EXPERIMENTAL DETAILS The ribbons of amorphous Fes0Cr2Si4B 14 (30 mm wide and about 30 ttm thick) were produced by a planar flow casting method at the Institute of Physics, Slovak Academy of Sciences in Bratislava. The samples were cut from the initial and the final parts of the amorphous ribbon each one with the total area of about 1.5 x 1.5 cm2. The total length of the ribbon produced from one batch was about 200 m and the terms "initial" and "final" refer to the parts of the ribbon taken approximately 10 m from the respective ends. A conventional constant acceleration M6ssbauer spectrometer with a 57Co(Rh) source was used in transmission geometry. Special attention was paid to the sample holder to avoid additional stresses. The M6ssbaner spectra were fitted by means of the NORMOS DIST program 6 to the distributions of hyperfine magnetic fields using 25 subsextets. Asymmetries in the spectral lines observed were covered by introducing linear correlations between the electric quadrupole interaction and the isomer shift, and between 321
322
MOSSBAUER STUDY OF THE SPIN ORIENTATION
the hyperfine magnetic splitting and the isomer shift. A linewidth of 0.26 mm/s, equal to the intrinsic linewidth of the spectrometer used, was assumed for all subspectra. The parameters obtained from the fit comprise along with the values of the hyperfine magnetic field, quadrupole shift, isomer shift and correlation parameters also the relative ratio of the M0ssbauer lines which was of the same value for all subsextets.
Vol~ 82, 1~. 5
z
A
5'/I
B
3. RESULTS AND DISCUSSION
:-y
Room temperature MOssbauer spectra of the FesoCr2Si4BI4 metallic glass in Fig.1 exhibit familiar six-line Zeeman-split patterns. Such broad and overlapped lines cause, however, some uncertainties in the determination of the line intensities (areas). This disadvantage can be minimized by a magic angle methodT, 8 which is able to give texture-free spectra 9 and, hence, accurate values of the hyperfine parameters can be determined. I0 Thus, the M0ssbauer spectra have been taken in three configurations as shown in Fig.2. Greneche and Varret 9 demonstrated that such arrangements are sufficient to calculate the spin populations Nx,
z
Fig.2. Orientations of the radiation propagation with respect to the plane of the amorphous ribbon.
Ny, Nz along the principal axes of the minimum texture: Nz = < cos2(~ >^ 2
I
.
.
.
.
.
I
.
.
.
I
.
.
.
.
I
.
.
.
.
I
1.00
Ny-Nx = ~(< COS2q~ >B-< COS2@R>C)
(l) (2)
where OR is the angle between the radiation direction and the nuclear quantization axis, and the indexes A, B and C denote the particular configurations as shown in Fig.2. The angle OR can be determined by measuring the relative line intensities in the MOssbauer spectra. For 57Fe experiments, the line ratios are given as:
0.95 1.00
i
g o.95 1.00
It:I2:I3:I4:I5:I6 = 3:b :l:l:b :3,
(3)
where 4 . sin2@R b = 1 + cos2OR
0.90 .
-10
.
.
.
t
-5
.
.
.
•
.
.
.
.
0
I
5
.
.
.
.
(4)
Ii
10
vetoca,/ (nm~s) Fig.1. MOssbauer spectra taken from the final part of the amorphous FesoCr2Si4Bl4 ribbon at room temperature in configurations A, B and C (see Fig.2).
is one of the fitted variables in the spectrum analysis. The parameter b oan vary between the values /7 = 0 which corresponds to OR = 0 ° and implies a parallel orientation of the spins with respect to the radiation direction, and b = 4 for OR = 90° when the spins are perpendicular to the T-rays. Examples of the M6ssbauer spectra
Vol. 82, No. 5
323
MOSSBAUBR STUDY OF THE SPIN ORIENTATION
Table 1 M~ssbauer and magnetic texture analysis of FeaoCrzSicBl4 metallic glass. The figure enclosed in brackets shows the error in the last digit. part of the
OH
OR"
ribbon
(T)
(T)
(deg)
Nx
Ny
Nz
initial
21.81(4) 4.30(5)
70.8(5)
0.426
0.466
0.108
0.647
final
21.80(3) 4.35(4)
74.9(47
0.421
0.511
0.068
0.620
a) OR-values derived from
recorded from the final part of the amorphous FesoCr2Si4B14 ribbon are depicted in Fig.1 and all the results are summarized in table 1. The average value, < H >, as well as the standard deviation, OH, of the hyperfine field distribution remained practically the same for the respective parts of the ribbon. The change in the angle OR, however, indicates a tendency Of magnetic moments to turn into the plane of the ribbon in its final part. This is also supported by the magnetic texture components - - namely by the out-of-plane spin population Nz. From the decrease of Nz it can be concluded that the in-plane anisotropy of the final part increases. 11 Parameters Nx and are assigned to the spin populations in the x-y plane, i.e. in the plane of the ribbon. Although there is practically no change in Nx, an increase in Ny implies that the in-plane anisotropy is rising toward the final part of the ribbon. The last column in table 1 gives a convenient check for testing the quality of the method. 9 The observed departures from the expected value of 2/3 are similar to those reported by other authors 9.12 and they might be due to a divergence of the 3' beam.9 To interpret the observed changes in the magnetic structure, deviations in the heat transfer during the quenching as well as geometrical aspects should be taken into account. The in-plane anisotropy can be ascribed to both quenching conditions and magnetostrictive properties 12 which influence the magnetic texture and the geometrical shape via the inhomogeneous solidification process, surface crystallizationll and local stresses within the ribbon. 5 As a consequence, the shape anisotropy of the specimen is affected and most of the magnetic moments are aligned parallel to the ribbon plane. The above mentioned parameters govern the magnetic structure of the initial
part of the ribbon,5 i.e., at the beginning of the preparation. However, the situation is different in the final part of the ribbon, i.e., toward the end of the technological cycle. Here, the decreased value of the out-of-plane spin population Nz together with a tendency of the net magnetic moment to turn closer to the ribbon plane, as detected by the MOssbauer effect experiments (see table 1), suggests that variations in the above mentioned parameters during the preparation of the sample are responsible for the changes observed. This result is in agreement with the implications from the magnetic measurements reported by Draganovsk~ et al. 5 who proposed an explanation of the differences between the initial and the final parts of the ribbon based on the directional atomic pair ordering.
4. CONCLUSIONS MOssbauer spectroscopy is a useful tool for studying magnetic structure on a nuclear level. The use of the magic angle method and the magnetic texture analysis allowed us to reveal differences between the initial and the final parts of the amorphous F~oCr2Si4BI4 ribbon. The population of the out-of-plane oriented spins is falling down toward the final part of the ribbon giving rise to an increase in the in-plane anisotropy. Such behaviour is supposed to be due to deviations in the conditions during the production of metallic glasses by a spinning technique. Acknowledgements - We are indebted to Dr.P. Duhaj for supplying us with the amorphous ribbons. MM gratefully appreciates the warm hospitality of Osaka University during the completing of the manuscript.
324
MOSSBAUI~ STUDY OF THE SPIN ORIENTATION
1. H. J. Bauer, U. Gonser & H. G. Wagner, Hyperflne Interactions 27, 401 (1986). 2. U. Goaser, H. J. Bauer & H. G.Wagner, J.Magn.Magn.Mater. 70, 419 (1987). 3. T. Limbach & U. Gonser, J.Non.Crystal.Solids 106, 399 (1988). 4. Y. M. Yamam, N. G. Kinikoglu & N. Aydinbeyli, J.Mater.Sci.Lett. 9, 460 (1990). 5. H. Draganovskt, J. Sl4ma, P. Butvin & B. Butvinov& phys. stat. solidi (a) 115, 533 (1989). 6. R. A. Brand, NOltMO$ Programs, Internal Report, Angewandte Physik, Universi~t Duisburg (1987).
Vol. 82, No. 5
7. H. D. Pfannes & H. Fischer, Appl.Phys. 13, 317 (1977). 8. J. M. Greneche, M. Henry & F. V a t , t, Int. Conf. on the Applications of the M6ssbauer Effect, p.908, Indian National Science Academy, New Delhi (1982). 9. J. M. Greneche & F. Varret, J.Phys.C.: Solid State Phys. 15, 5333 (1982). 10. J. M. Gmneche & F. Varret, Solid State Commun. 54, 985 (1985). 11. P. Auric, J. M. Greneche, O. deBouvier & J. J. Rameau, J.Magn.Magn.Mater. 82, 243 (1989). 12. M. Henry, M. Bourrous, F. Varret & P. Founier, J.Mater.Sci. 19, 1000 (1984).