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Magnetic aftereffects in ion-implanted metallic glasses
Journal
of Magnetism
MAGNETIC A. COLLINS, Department
and Magnetic
Materials
54-57
AFTEREFFECTS R.C. O’HANDLEY
of Moteriuls
2x1
(1986) 281-282
IN ION-IMPLANTED
METALLIC
GLASSES
and N.J. GRANT
Scrence and Engrneerrng, Massachusetts
Insrtute
of Technologv. Camhndge. MA 02139, USA
Magnetic aftereffects have been studied in iron-base and cobalt-base metallic glasses ion-implanted Conmlex relaxation spectra are observed and specific peaks can be identified as being due to boron to diffusional processes.
1. Introduction
The most direct characterization of atomic arrangements in glasses have come from scattering studies (X-ray, neutron, electron). However, the angular arrangements of atoms (bond orientational order) in amorphous solids cannot be uniquely determined from these experiments. Scattering measurements provide statistical descriptions of the atomic arrangements, and thus should be supplemented by experiments sensitive to local symmetry and by three-dimensional structural models. This paper reports the use of a magnetic relaxation method to probe the short-range order (SRO) but with one important new feature: introduction of specific interstitials by ion implantation. The Magnetic AfterEffects (MAE’s) caused by the implanted interstitials provide information about the local ordering, the interaction between interstitial and glass and the stability of the glass. 2. Experimental The amorphous alloys were prepared by melt-spinning. The presence of glassy phase was established by X-ray scattering. B. or N ions were implanted with an energy of 100 keV to a dose of lOI ions/cm2. Liquid N, cooling was used to remove the thermal energy and avoid crystallization during implantation. Secondary Ion Mass Spectroscopy (SIMS) data of the implanted samples showed an implantation depth of 50 A. The samples were annealed at Tot = 340°C for 24 h in order to remove internal stresses and restore the possible damages caused by the implantation. Magnetic relaxation was measured using a GenRad Digibridge after the samples’ initial state was set by application of a dc saturating pulse. The measuring field was provided by a long solenoid, whose axis was parallel to the ribbon length. The field intensity was smaller than 1 mOe. The time and temperature dependence of the permeability was measured as a set of isothermal relaxation curves. The temperature was varied from * This work is supported by the 3-M Company.
0304-8853/86/$03.50
*
0 Elsevier Science Publishers
with boron and nitrogen. reorientation processes or
room temperature up to 300°C and the time range used was t, = 20 s to r2 usually = 240 s. The relaxation spectra are represented as isochronal relaxation curves of Ap./p versus temperature, where AP/P=
[PL(~O)-P(~~)]/P(~O).
where ~(20) and p( t2) are the permeability and at tz s after demagnetization.
values at 20
3. Results and discussion Fig. 1 shows the isochronals of amorphous Fe,,B,,Si, and Fe,,B,,Si, implanted with B. We distinguish three maxima centered at 150, 230 and 27O”C, respectively. They indicate three main relaxation processes. In general relaxation can be due to diffusion or reorientation processes (or both) associated with a certain atom or atom pair [l]. The different mechanisms are distinguished by their time dependence. The isothermals of a reorientation process can be described by exponential time law x,, - ee”‘, whereas a diffusion process is distinguished by the x0 - /6” law (for r>To). Analysis of the isothermals at 150 and 230°C shows that they follow the exponential time law. Therefore they are due mostly to a reorientation mechanism. The
01
‘00
150
200
250
300
Temperature (“Cl
Fig. 7. Fe,,B,,Si,
B.V.
lsochronal implanted
relaxation with B.
curves
of
Fe,,B,,Si,
and
282
A. Colltrts et 01. / Aftereffects
in ton -rmplunted
mrtdlic
glasses
addition to this, the Co,,Nb,,$ glass exhibit a nnniat 150°C. The tmplantatton of Co,,Fe,,, MO, 4 Ni,,,B,,Si,, with N caused a decrease of the relaxation amplitude due to the reduction of the free volume by N. However the B implantation on Co,,Nb,,$ increased the intensity of the aftereffects. From these observations we conclude that B is responsible for the relaxation process at 290°C in the Co-base glasses. Analysis of the time dependence of the isothermal at 290°C shows that it is of mixed diffusion and reorientation nature. The minimum at 150°C in the Co,,Nb,,$ spectrum could be related to the structural transformation first observed by Corb et al. [4]. Comparison of figs. 1 and 2 shows that the amplitude of the relaxation spectra for Fe-base glasses is greater and richer in structure than that for Co-base glasses. It is known that the magnetostriction X is greater for Fe-base than for Co-base glasses. Thus our results are consistent with models attributing a large part of the MAE’s to magnetoelastic effects (strain dipoles) [5]. In particular we associate the reorientation peaks in Fe-base glasses (150, 230°C) with strain dipole effects. This suggests that these peaks are absent in the zero-magnetostriction cobalt-base glasses. The diffusional (or mixed in the case of cobalt-base glasses) peak at higher temperature (less dependent on magnetostriction) are present in both the Fe-base and Co-base glasses. mum
70.5
I
”
I
100
I
150
I
I
200
250
I
I
300
Temoerature (“C) Fig. 2. Isochronal glasses.
relaxation
spectra
of cobalt-base
implanted
process that occurs at 270°C has the rm3i’ law dependence and is due mostly to diffusion. This is in agreement with the fact that diffusion generally occurs at higher temperature than does reorientation. Comparing the isochronal of the sample implanted with B with the isochronal of the unimplanted sample we observe a decrease in the intensity of the 230 and 270°C peaks upon implantation of B. Implantation of B, though, increased the relaxation amplitude of the 150°C reorientation peak. We assume, therefore, that the process at 150°C is due to B reorientation. This is in agreement with the results for Fe,,B,,], where the same maximum was observed [3]. The isochronals of Co-base (Co,,Nb,,$ and Co,,Fe,,,Mo,,,N,,B,,Si,,) and of implanted Co-base (Co,,implanted with B and Co,,Fe,,,Nb,,B, implanted with N) are shown in fig. Mot.,Nit SB,ISiI, 2. We observe a maximum centered near 290°C. In
[l] N. Moser and H. Kronmuller, [2] [3] [4] [5]
J. Magn. Magn. Mat. 19 (1980) 275. R.C. O’Handley, C-P Chou and N. DeCristofaro. J. Appl. Phys. 50 (1979) 3603. F. Rettenmeier. Diplomarbeit. University of Stuttgart (1982). B.W. Corb, R.C. O’Handley, J. Megusar and N.J. Grant. J. Appl. Phys. 55 (1984) 1808. P. Allia and F. Vinai. Phys. Rev. B26 (1982) 6141.
of Magnetism
MAGNETIC A. COLLINS, Department
and Magnetic
Materials
54-57
AFTEREFFECTS R.C. O’HANDLEY
of Moteriuls
2x1
(1986) 281-282
IN ION-IMPLANTED
METALLIC
GLASSES
and N.J. GRANT
Scrence and Engrneerrng, Massachusetts
Insrtute
of Technologv. Camhndge. MA 02139, USA
Magnetic aftereffects have been studied in iron-base and cobalt-base metallic glasses ion-implanted Conmlex relaxation spectra are observed and specific peaks can be identified as being due to boron to diffusional processes.
1. Introduction
The most direct characterization of atomic arrangements in glasses have come from scattering studies (X-ray, neutron, electron). However, the angular arrangements of atoms (bond orientational order) in amorphous solids cannot be uniquely determined from these experiments. Scattering measurements provide statistical descriptions of the atomic arrangements, and thus should be supplemented by experiments sensitive to local symmetry and by three-dimensional structural models. This paper reports the use of a magnetic relaxation method to probe the short-range order (SRO) but with one important new feature: introduction of specific interstitials by ion implantation. The Magnetic AfterEffects (MAE’s) caused by the implanted interstitials provide information about the local ordering, the interaction between interstitial and glass and the stability of the glass. 2. Experimental The amorphous alloys were prepared by melt-spinning. The presence of glassy phase was established by X-ray scattering. B. or N ions were implanted with an energy of 100 keV to a dose of lOI ions/cm2. Liquid N, cooling was used to remove the thermal energy and avoid crystallization during implantation. Secondary Ion Mass Spectroscopy (SIMS) data of the implanted samples showed an implantation depth of 50 A. The samples were annealed at Tot = 340°C for 24 h in order to remove internal stresses and restore the possible damages caused by the implantation. Magnetic relaxation was measured using a GenRad Digibridge after the samples’ initial state was set by application of a dc saturating pulse. The measuring field was provided by a long solenoid, whose axis was parallel to the ribbon length. The field intensity was smaller than 1 mOe. The time and temperature dependence of the permeability was measured as a set of isothermal relaxation curves. The temperature was varied from * This work is supported by the 3-M Company.
0304-8853/86/$03.50
*
0 Elsevier Science Publishers
with boron and nitrogen. reorientation processes or
room temperature up to 300°C and the time range used was t, = 20 s to r2 usually = 240 s. The relaxation spectra are represented as isochronal relaxation curves of Ap./p versus temperature, where AP/P=
[PL(~O)-P(~~)]/P(~O).
where ~(20) and p( t2) are the permeability and at tz s after demagnetization.
values at 20
3. Results and discussion Fig. 1 shows the isochronals of amorphous Fe,,B,,Si, and Fe,,B,,Si, implanted with B. We distinguish three maxima centered at 150, 230 and 27O”C, respectively. They indicate three main relaxation processes. In general relaxation can be due to diffusion or reorientation processes (or both) associated with a certain atom or atom pair [l]. The different mechanisms are distinguished by their time dependence. The isothermals of a reorientation process can be described by exponential time law x,, - ee”‘, whereas a diffusion process is distinguished by the x0 - /6” law (for r>To). Analysis of the isothermals at 150 and 230°C shows that they follow the exponential time law. Therefore they are due mostly to a reorientation mechanism. The
01
‘00
150
200
250
300
Temperature (“Cl
Fig. 7. Fe,,B,,Si,
B.V.
lsochronal implanted
relaxation with B.
curves
of
Fe,,B,,Si,
and
282
A. Colltrts et 01. / Aftereffects
in ton -rmplunted
mrtdlic
glasses
addition to this, the Co,,Nb,,$ glass exhibit a nnniat 150°C. The tmplantatton of Co,,Fe,,, MO, 4 Ni,,,B,,Si,, with N caused a decrease of the relaxation amplitude due to the reduction of the free volume by N. However the B implantation on Co,,Nb,,$ increased the intensity of the aftereffects. From these observations we conclude that B is responsible for the relaxation process at 290°C in the Co-base glasses. Analysis of the time dependence of the isothermal at 290°C shows that it is of mixed diffusion and reorientation nature. The minimum at 150°C in the Co,,Nb,,$ spectrum could be related to the structural transformation first observed by Corb et al. [4]. Comparison of figs. 1 and 2 shows that the amplitude of the relaxation spectra for Fe-base glasses is greater and richer in structure than that for Co-base glasses. It is known that the magnetostriction X is greater for Fe-base than for Co-base glasses. Thus our results are consistent with models attributing a large part of the MAE’s to magnetoelastic effects (strain dipoles) [5]. In particular we associate the reorientation peaks in Fe-base glasses (150, 230°C) with strain dipole effects. This suggests that these peaks are absent in the zero-magnetostriction cobalt-base glasses. The diffusional (or mixed in the case of cobalt-base glasses) peak at higher temperature (less dependent on magnetostriction) are present in both the Fe-base and Co-base glasses. mum
70.5
I
”
I
100
I
150
I
I
200
250
I
I
300
Temoerature (“C) Fig. 2. Isochronal glasses.
relaxation
spectra
of cobalt-base
implanted
process that occurs at 270°C has the rm3i’ law dependence and is due mostly to diffusion. This is in agreement with the fact that diffusion generally occurs at higher temperature than does reorientation. Comparing the isochronal of the sample implanted with B with the isochronal of the unimplanted sample we observe a decrease in the intensity of the 230 and 270°C peaks upon implantation of B. Implantation of B, though, increased the relaxation amplitude of the 150°C reorientation peak. We assume, therefore, that the process at 150°C is due to B reorientation. This is in agreement with the results for Fe,,B,,], where the same maximum was observed [3]. The isochronals of Co-base (Co,,Nb,,$ and Co,,Fe,,,Mo,,,N,,B,,Si,,) and of implanted Co-base (Co,,implanted with B and Co,,Fe,,,Nb,,B, implanted with N) are shown in fig. Mot.,Nit SB,ISiI, 2. We observe a maximum centered near 290°C. In
[l] N. Moser and H. Kronmuller, [2] [3] [4] [5]
J. Magn. Magn. Mat. 19 (1980) 275. R.C. O’Handley, C-P Chou and N. DeCristofaro. J. Appl. Phys. 50 (1979) 3603. F. Rettenmeier. Diplomarbeit. University of Stuttgart (1982). B.W. Corb, R.C. O’Handley, J. Megusar and N.J. Grant. J. Appl. Phys. 55 (1984) 1808. P. Allia and F. Vinai. Phys. Rev. B26 (1982) 6141.