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Mössbauer studies of amorphous iron and metglas 2826 MB
M O S S B A U E R S T U D I E S OF A M O R P H O U S I R O N AND M E T G L A S 2826 MB S. B J A R M A N , R. K A M A L and R. W A P P L I N G Institute of Physics, Uppsala University, Box 530, S-751 21 Uppsala, Sweden
Sputtered iron films have been prepared at room temperature. On a metallic substrate the films become amorphous and stable to about 500 K. Characterization of the films have been made by Mossbauer spectroscopy a n d electron diffraction. Mossbauer measurements have also been performed on Metglas 2826 MB showing a complex behaviour in the 600 K range. At temperatures below 200 K a spin wave behaviour is found with the Bloch constant a = 62 × 10 - 6 K -3/2.
1. Preparation and measurements
7.
....".. .:..-,.,
16oT Iron films of thicknesses up to 1 m g / c m 2 have been prepared by ion b e a m sputtering at room temperature. Using similar apparatus as described by Sletten et al. [l] and a good thermal conductor as a substrate, the films show no trace of crystalline iron in the M r s s b a u e r spectra (fig. 1). Electron diffractograms of the same films also confirm the amorphous characterization. The purity has been checked by Rutherford backscattering analysis [2]. Impurities heavier than 12C have been found to be much less than 1 at.%. Films sputtered on a glass substrate do not show the amorphous characteristics but rather those of distorted crystalline a-iron. The Mrssbauer studies were made using both conversion electron scattering and transmission geometries together with a conventional constant acceleration drive. The same equipment was used in the measurements on the Metglas. Spectra of both materials were recorded at various temperatures using a vacuum furnace and a helium flow cryostat. In the iron case the crystallization temperature was found by making heat treatments at subsequently higher temperatures followed by M r s s b a u e r recordings at room temperature. After 2 h in H 2 atm. at 530 K only small traces of amorphous iron were found superimposed on the usual a-iron spectrum (fig. 2). More heat treatments and recordings will be made on this system and the results will be published elsewhere together with results from Hall-effect and resistivity measurements. Spectra from the 2826 MB Metglas were recorded while heating from 10 K up to 600 K, while cooling to 300 K, and while reheating to above 600 K. All spectra from 10 to 520 K display a similar distribution in the magnetic hyperfine field following the usual decrease in the mean field value with temperature. At 540 K only a quadrupole doublet
130 j__j/,. ./: J" /~J 1O 0 -8
-3
0
3
'~-6
VELOCITY MM/S
Fig. 1. Mossbauer spectrum of 57Fe sputtered on aluminium; before heat treatment.
7.
200t
.
lso]
i
/
lootj
.'. .
... 'J ,.J
-6
-3 0 VELOCITY
•
i
~, .,j .~ 3 6 MM/S
Fig. 2. M r s s b a u e r spectrum of 57Fe sputtered on aluminium; after heat treatment at 530 K.
is seen. Going down in temperature no magnetic splitting is seen until 460 K and below. Here the spectra indicate a partly crystallized material. On reheating the same ordering temperature is seen as while cooling, indicating a lower Curie point for the crystalline phase than for the amorphous one.
2. Discussion A film composed of size distributed very small iron crystals would show a similar distribution in the magnetic field as an amorphous film because of different Curie temperatures for different grain sizes. On the other hand, only grains exceeding some critical volume would show any magnetic field at all and there would not be any distribution in the saturation field. The broad distribution at even very low temperatures (5 K) contradicts this
Journal of Magnetism and Magnetic Materials 15-18 (1980) 1389-1390 ©North Holland
1389
1390
S. Bjarman et al./ Mossbauer studies of amorphous iron
e x p l a n a t i o n a n d leaves the a m o r p h o u s structure as the only one possible. In the analysis of the i r o n spectra we have f o u n d a small b u t significant a s y m m e t r y . The n a t u r e of this a s y m m e t r y can o n l y be explained by a d i s t r i b u t i o n in the isomer shift. A possible c o r r e l a t i o n b e t w e e n the i s o m e r shift a n d the m a g n e t i c field in an a m o r p h o u s f e r r o m a g n e t is an interesting subject for further studies. In the case of the M e t g l a s we have a n a l y s e d the m e a n field t e m p e r a t u r e d e p e n d e n c e a n d f o u n d clear evidence of spin wave b e h a v i o u r . This is shown b y the Bloch T 3/2 law: A M ( T ) / M(O) = e~T 3/2,
where we f o u n d c~ = 62 × 10 - 6 K -3/2, a rather high c o n s t a n t c o m p a r e d to o t h e r M e t g l a s systems
[3-5].
References [1] G. Sletten and P. Knudsen, Nucl. Instr. and Meth. 102 (1972) 459. [21 S. Penersson et al., Nucl. Instr. and Meth. 149 (1978) 285. [3] C. C. Tsuei and H. Lilienthal, Phys. Rev. 13 (1978) 4899. [4] C. L. Chien and R. Hasegawa, Hyp. Int. 4 (1978) 866. [5] C. L. Chien, Phys. Rev. 18 (1978) 1003.
Sputtered iron films have been prepared at room temperature. On a metallic substrate the films become amorphous and stable to about 500 K. Characterization of the films have been made by Mossbauer spectroscopy a n d electron diffraction. Mossbauer measurements have also been performed on Metglas 2826 MB showing a complex behaviour in the 600 K range. At temperatures below 200 K a spin wave behaviour is found with the Bloch constant a = 62 × 10 - 6 K -3/2.
1. Preparation and measurements
7.
....".. .:..-,.,
16oT Iron films of thicknesses up to 1 m g / c m 2 have been prepared by ion b e a m sputtering at room temperature. Using similar apparatus as described by Sletten et al. [l] and a good thermal conductor as a substrate, the films show no trace of crystalline iron in the M r s s b a u e r spectra (fig. 1). Electron diffractograms of the same films also confirm the amorphous characterization. The purity has been checked by Rutherford backscattering analysis [2]. Impurities heavier than 12C have been found to be much less than 1 at.%. Films sputtered on a glass substrate do not show the amorphous characteristics but rather those of distorted crystalline a-iron. The Mrssbauer studies were made using both conversion electron scattering and transmission geometries together with a conventional constant acceleration drive. The same equipment was used in the measurements on the Metglas. Spectra of both materials were recorded at various temperatures using a vacuum furnace and a helium flow cryostat. In the iron case the crystallization temperature was found by making heat treatments at subsequently higher temperatures followed by M r s s b a u e r recordings at room temperature. After 2 h in H 2 atm. at 530 K only small traces of amorphous iron were found superimposed on the usual a-iron spectrum (fig. 2). More heat treatments and recordings will be made on this system and the results will be published elsewhere together with results from Hall-effect and resistivity measurements. Spectra from the 2826 MB Metglas were recorded while heating from 10 K up to 600 K, while cooling to 300 K, and while reheating to above 600 K. All spectra from 10 to 520 K display a similar distribution in the magnetic hyperfine field following the usual decrease in the mean field value with temperature. At 540 K only a quadrupole doublet
130 j__j/,. ./: J" /~J 1O 0 -8
-3
0
3
'~-6
VELOCITY MM/S
Fig. 1. Mossbauer spectrum of 57Fe sputtered on aluminium; before heat treatment.
7.
200t
.
lso]
i
/
lootj
.'. .
... 'J ,.J
-6
-3 0 VELOCITY
•
i
~, .,j .~ 3 6 MM/S
Fig. 2. M r s s b a u e r spectrum of 57Fe sputtered on aluminium; after heat treatment at 530 K.
is seen. Going down in temperature no magnetic splitting is seen until 460 K and below. Here the spectra indicate a partly crystallized material. On reheating the same ordering temperature is seen as while cooling, indicating a lower Curie point for the crystalline phase than for the amorphous one.
2. Discussion A film composed of size distributed very small iron crystals would show a similar distribution in the magnetic field as an amorphous film because of different Curie temperatures for different grain sizes. On the other hand, only grains exceeding some critical volume would show any magnetic field at all and there would not be any distribution in the saturation field. The broad distribution at even very low temperatures (5 K) contradicts this
Journal of Magnetism and Magnetic Materials 15-18 (1980) 1389-1390 ©North Holland
1389
1390
S. Bjarman et al./ Mossbauer studies of amorphous iron
e x p l a n a t i o n a n d leaves the a m o r p h o u s structure as the only one possible. In the analysis of the i r o n spectra we have f o u n d a small b u t significant a s y m m e t r y . The n a t u r e of this a s y m m e t r y can o n l y be explained by a d i s t r i b u t i o n in the isomer shift. A possible c o r r e l a t i o n b e t w e e n the i s o m e r shift a n d the m a g n e t i c field in an a m o r p h o u s f e r r o m a g n e t is an interesting subject for further studies. In the case of the M e t g l a s we have a n a l y s e d the m e a n field t e m p e r a t u r e d e p e n d e n c e a n d f o u n d clear evidence of spin wave b e h a v i o u r . This is shown b y the Bloch T 3/2 law: A M ( T ) / M(O) = e~T 3/2,
where we f o u n d c~ = 62 × 10 - 6 K -3/2, a rather high c o n s t a n t c o m p a r e d to o t h e r M e t g l a s systems
[3-5].
References [1] G. Sletten and P. Knudsen, Nucl. Instr. and Meth. 102 (1972) 459. [21 S. Penersson et al., Nucl. Instr. and Meth. 149 (1978) 285. [3] C. C. Tsuei and H. Lilienthal, Phys. Rev. 13 (1978) 4899. [4] C. L. Chien and R. Hasegawa, Hyp. Int. 4 (1978) 866. [5] C. L. Chien, Phys. Rev. 18 (1978) 1003.