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The influence of plastic deformation on the spin-glass in Fe-37.0 at.% Al compound
30 January 1995 PHYSICS LETTERS A
Physics Letters A 197 (1995) 350-352
ELSEVIER
The influence of plastic deformation on the spin-glass in Fe-37.0 at.% A1 compound S. Takahashi, A. Chiba, E. Takahashi Faculty of Engineering, lwate University, Morioka 020, Japan
Received 16 September 1994; accepted for publication 22 November 1994 Communicatedby J. Flouquet
Abstract
Magnetization was measured in plastically deformed 37.0 at.% A1-Fe compounds in the temperature range from 4.5 to 61 K. Plastic deformation makes the spin-glass state increase; the frozen temperature changes from 32 to 37.5 K with 10% strain. The APB between superpartial dislocations plays an important role in this enhancement.
Fel_xAl~ intermetallic compounds have three magnetic states; the paramagnetic state, the ferromagnetic state and the spin-glass. The spin-glass in Fel_xAl~ has been investigated experimentally and theoretically by many investigators [ 1-3 ]. The spinglass state in these compounds was observed at sufficiently low temperature for 0.27~
dislocation density, p. And the relationship has been examined experimentally by one of the present authors and his coworker [ 7 ]. The purpose of the present study is to investigate the influence of plastic deformation on the spin-glass state in Fel_xAl~ compounds. A new experimental fact has been found in the spin-glass state of plastically deformed samples; the frozen temperature increases as the plastic strain increases. The raw materials used for alloying in the present investigation were 99.998 mass% A1 and 99.95 mass% Fe. Alloy "buttons" with the nominal composition 37.0 at.% A1-Fe were prepared by arc-melting the raw materials four times to attain chemical homogeneity on a water-cooled copper hearth in an argon gas atmosphere at a pressure of approximately 93 kPa. The buttons were homogenized at 973 K for two days. The samples with a dimension of approximately 2.5X2.5X5.0 m m 3 were cut from the button ingot and chemically polished to remove surface damages. Samples for the magnetic measurement were formed with a dimension of 2.5 • 2.5 X 2.5 m m 3. The steadyfield magnetization was measured by SQUID mag-
0375-9601/95/$09.50 9 1995 ElsevierScience B.V. All rights reserved SSD10375-9601 (94) 00959-7
S. Takahashi et al. / Physics Letters A 197 (1995) 350-352
netic flux-meter (Quantum Design) in the temperature range from 4.5 to 61 K. Thin foils for electron microscopy investigation were prepared using a standard jet-electropolishing technique. Superlattice dislocations were observed in the foil on a 200 kV transmission electron microscope. Fig. 1 shows the magnetization versus temperature at 100 Oe for Fe-37.0 at.% A1 compounds without plastic deformation (A) and with plastic deformation of e = 5 % (B) and 10% (C). The thermomagnetic curves were measured by two processes; cooled to 4.5 K in zero field, the measurements were made in a sequence of increasing temperatures (open circles), and samples were cooled and measured at a field of 100 Oe (solid circles). These steady-field magnetization curves show very clearly the thermomagnetic history effect typical for the spin-glass [ 2 ]. The cusp in the thermomagnetization curve corresponds to the frozen temperature, Tf, according to the previous investigators [1,2]. Plastic deformation makes the magnetization (the magnetic susceptibility) increase and the cusp becomes sharp. Tf or the temperature of the cusp increases slightly with increasing plastic strain. The increase of Tf due to plastic deformation could be admitted in other compounds with x=0.35, 0.39 and 0.40.
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The plastic deformation gives a direct influence on the spin-glass state and the dislocation structure has been observed with the electron microscope. Fig. 2 shows the electron micrograph of 37.0 at.% A1-Fe compound deformed plastically by e--5%. The electron microscopy observation indicates that the paired dislocations are distributed on the { 110} glide planes; the separation of partial dislocations is 6 nm in the screw component. The value o f p was measured b y counting the intersection of dislocation lines with straight lines drawn randomly on photographic films. p is approximately 8 X 10 9 c m - 2 in the samples with = 5%. These superlattice dislocations have APB between superpartials. In the vicinity of APB, the arrangement of Fe and A1 atoms is different from that in the atomically ordered state; Fe atoms on the ixsite are arranged in a chain with the nearest neighhour. These chained Fe atoms are coupled ferromagnetically above Tr [6,7 ]. The magnetic phase diagram for Fel _xAlx shows that the paramagnetic, ferromagnetic and spin-glass phases meet at a multicritical point in the vicinity of the A1 concentration x = 0.30. The ferromagnetic order changes to the spin-glass for 0 . 2 7 ~ x ~ 0 . 3 0 at sufficiently low temperature [ 3 ], where the magnetic moments are frozen for various orientations without long range order. Before plastic deformation, the paramagnetic state changes to the spin-glass at Tf= 32 K in the present samples. In the plastically deformed samples, there exist two magnetic states above Tf, ferromagnetic clusters locate along the APB ribbons between superpartials and the paramagnetic state exists apart from the APB ribbons [7]. These paramagnetic and fer-
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Temperature (K)
Fig. 1. Magnetizationversus temperature at 100 Oe for 37.0 at.% AI-Fe compound without plastic deformation (A) and with plasticdeformationof 5% (B) and 10% (C). Sampleswere cooled to 4.5 K under zero field, measurementswere made in a sequence of increasing temperatures (open circles), samples were cooled and measured under 50 Oe field (solid circles).
Fig. 2. The electron micrograph of 37.0 at.% A1-Fe compound deformed to a strain of 5.0%.
352
S. Takahashi et al. / Physics Letters A 197 (1995) 350-352
romagnetic states change to the spin-glass at Tf in the plastically deformed samples. The value of Tf is not necessarily the same for the two transitions. The experimental value of Tf is observed as the average of these values. More exactly, two cusps would be observed if the values of Tf are sufficiently different and the cusp would become vague if the values are not sufficiently different. The present result is contrary to the expectation; one cusp becomes sharp and the temperature of the cusp increases as plastic deformation advances. Tf of the 10% strained sample is 37.5 K. The magnetic susceptibility or the magnetization at 100 Oe of plastically deformed samples is very large compared to that of the undeformed one, though the volume of APB ribbons is less than 10- 3% of the total volume in the sample with ~= 5%. The spin-glass state in the APB ribbon is different from that of the B2type ordered state; the magnetic susceptibility in the spin-glass state increases considerably by introduction of APB ribbons. The susceptibility in the APB ribbons would be 105 times as large as that of the B2type ordered state, if there exist two spin-glass states independently. The large susceptibility in the plastically deformed samples suggests that there remains the ferromagnetic ordered state along the APB ribbons even in the temperature range between 4.5 and
37.5 K. The ferromagnetic APB ribbons give some magnetic influence to the neighbouring spin-glass state and change the value of Tf. The value of Tr depends on the AI content in Fe~_xAlx compounds as the plastic deformation effect. The magnetic susceptibility increases and the cusp of the magnetization curves becomes vague as the AI content decreases [2 ]. Plastic deformation, however, produces a different effect in the thermomagnetic curves; the susceptibility increases and the cusp becomes sharp as the plastic deformation advances. The influence of plastic deformation on the spin-glass is characterized by ferromagnetic clusters in the APB ribbons. A detailed study is now in progress.
References [ 1 ] H. Okamoto and P.A. Beck, Metall. Trans. 2 ( 1971 ) 569. [2] R.D. Shull, H. Okamoto and P.A. Beck, Solid State Commun. 20 (1976) 863. [ 3 ] P. Shukla and M. Wortis, Phys. Rev. B 21 (1980) 159. [4] J.S. Kouvel, J. Appl. Phys. 30 (1959) 313S. [5] M.J. Besnus, A. Herr and A.J. Meyer, J. Phys. F 5 (1975) 2138. [6] S. Takahashi, J. Magn. Magn. Mater. 54-56 (1986) 1065. [7] S. Takahashi and Y. Umakoshi, J. Phys. Condens. Matt. 3 (1991) 5805.
Physics Letters A 197 (1995) 350-352
ELSEVIER
The influence of plastic deformation on the spin-glass in Fe-37.0 at.% A1 compound S. Takahashi, A. Chiba, E. Takahashi Faculty of Engineering, lwate University, Morioka 020, Japan
Received 16 September 1994; accepted for publication 22 November 1994 Communicatedby J. Flouquet
Abstract
Magnetization was measured in plastically deformed 37.0 at.% A1-Fe compounds in the temperature range from 4.5 to 61 K. Plastic deformation makes the spin-glass state increase; the frozen temperature changes from 32 to 37.5 K with 10% strain. The APB between superpartial dislocations plays an important role in this enhancement.
Fel_xAl~ intermetallic compounds have three magnetic states; the paramagnetic state, the ferromagnetic state and the spin-glass. The spin-glass in Fel_xAl~ has been investigated experimentally and theoretically by many investigators [ 1-3 ]. The spinglass state in these compounds was observed at sufficiently low temperature for 0.27~
dislocation density, p. And the relationship has been examined experimentally by one of the present authors and his coworker [ 7 ]. The purpose of the present study is to investigate the influence of plastic deformation on the spin-glass state in Fel_xAl~ compounds. A new experimental fact has been found in the spin-glass state of plastically deformed samples; the frozen temperature increases as the plastic strain increases. The raw materials used for alloying in the present investigation were 99.998 mass% A1 and 99.95 mass% Fe. Alloy "buttons" with the nominal composition 37.0 at.% A1-Fe were prepared by arc-melting the raw materials four times to attain chemical homogeneity on a water-cooled copper hearth in an argon gas atmosphere at a pressure of approximately 93 kPa. The buttons were homogenized at 973 K for two days. The samples with a dimension of approximately 2.5X2.5X5.0 m m 3 were cut from the button ingot and chemically polished to remove surface damages. Samples for the magnetic measurement were formed with a dimension of 2.5 • 2.5 X 2.5 m m 3. The steadyfield magnetization was measured by SQUID mag-
0375-9601/95/$09.50 9 1995 ElsevierScience B.V. All rights reserved SSD10375-9601 (94) 00959-7
S. Takahashi et al. / Physics Letters A 197 (1995) 350-352
netic flux-meter (Quantum Design) in the temperature range from 4.5 to 61 K. Thin foils for electron microscopy investigation were prepared using a standard jet-electropolishing technique. Superlattice dislocations were observed in the foil on a 200 kV transmission electron microscope. Fig. 1 shows the magnetization versus temperature at 100 Oe for Fe-37.0 at.% A1 compounds without plastic deformation (A) and with plastic deformation of e = 5 % (B) and 10% (C). The thermomagnetic curves were measured by two processes; cooled to 4.5 K in zero field, the measurements were made in a sequence of increasing temperatures (open circles), and samples were cooled and measured at a field of 100 Oe (solid circles). These steady-field magnetization curves show very clearly the thermomagnetic history effect typical for the spin-glass [ 2 ]. The cusp in the thermomagnetization curve corresponds to the frozen temperature, Tf, according to the previous investigators [1,2]. Plastic deformation makes the magnetization (the magnetic susceptibility) increase and the cusp becomes sharp. Tf or the temperature of the cusp increases slightly with increasing plastic strain. The increase of Tf due to plastic deformation could be admitted in other compounds with x=0.35, 0.39 and 0.40.
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c
351
The plastic deformation gives a direct influence on the spin-glass state and the dislocation structure has been observed with the electron microscope. Fig. 2 shows the electron micrograph of 37.0 at.% A1-Fe compound deformed plastically by e--5%. The electron microscopy observation indicates that the paired dislocations are distributed on the { 110} glide planes; the separation of partial dislocations is 6 nm in the screw component. The value o f p was measured b y counting the intersection of dislocation lines with straight lines drawn randomly on photographic films. p is approximately 8 X 10 9 c m - 2 in the samples with = 5%. These superlattice dislocations have APB between superpartials. In the vicinity of APB, the arrangement of Fe and A1 atoms is different from that in the atomically ordered state; Fe atoms on the ixsite are arranged in a chain with the nearest neighhour. These chained Fe atoms are coupled ferromagnetically above Tr [6,7 ]. The magnetic phase diagram for Fel _xAlx shows that the paramagnetic, ferromagnetic and spin-glass phases meet at a multicritical point in the vicinity of the A1 concentration x = 0.30. The ferromagnetic order changes to the spin-glass for 0 . 2 7 ~ x ~ 0 . 3 0 at sufficiently low temperature [ 3 ], where the magnetic moments are frozen for various orientations without long range order. Before plastic deformation, the paramagnetic state changes to the spin-glass at Tf= 32 K in the present samples. In the plastically deformed samples, there exist two magnetic states above Tf, ferromagnetic clusters locate along the APB ribbons between superpartials and the paramagnetic state exists apart from the APB ribbons [7]. These paramagnetic and fer-
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l0
20
30
40
50
60
70
Temperature (K)
Fig. 1. Magnetizationversus temperature at 100 Oe for 37.0 at.% AI-Fe compound without plastic deformation (A) and with plasticdeformationof 5% (B) and 10% (C). Sampleswere cooled to 4.5 K under zero field, measurementswere made in a sequence of increasing temperatures (open circles), samples were cooled and measured under 50 Oe field (solid circles).
Fig. 2. The electron micrograph of 37.0 at.% A1-Fe compound deformed to a strain of 5.0%.
352
S. Takahashi et al. / Physics Letters A 197 (1995) 350-352
romagnetic states change to the spin-glass at Tf in the plastically deformed samples. The value of Tf is not necessarily the same for the two transitions. The experimental value of Tf is observed as the average of these values. More exactly, two cusps would be observed if the values of Tf are sufficiently different and the cusp would become vague if the values are not sufficiently different. The present result is contrary to the expectation; one cusp becomes sharp and the temperature of the cusp increases as plastic deformation advances. Tf of the 10% strained sample is 37.5 K. The magnetic susceptibility or the magnetization at 100 Oe of plastically deformed samples is very large compared to that of the undeformed one, though the volume of APB ribbons is less than 10- 3% of the total volume in the sample with ~= 5%. The spin-glass state in the APB ribbon is different from that of the B2type ordered state; the magnetic susceptibility in the spin-glass state increases considerably by introduction of APB ribbons. The susceptibility in the APB ribbons would be 105 times as large as that of the B2type ordered state, if there exist two spin-glass states independently. The large susceptibility in the plastically deformed samples suggests that there remains the ferromagnetic ordered state along the APB ribbons even in the temperature range between 4.5 and
37.5 K. The ferromagnetic APB ribbons give some magnetic influence to the neighbouring spin-glass state and change the value of Tf. The value of Tr depends on the AI content in Fe~_xAlx compounds as the plastic deformation effect. The magnetic susceptibility increases and the cusp of the magnetization curves becomes vague as the AI content decreases [2 ]. Plastic deformation, however, produces a different effect in the thermomagnetic curves; the susceptibility increases and the cusp becomes sharp as the plastic deformation advances. The influence of plastic deformation on the spin-glass is characterized by ferromagnetic clusters in the APB ribbons. A detailed study is now in progress.
References [ 1 ] H. Okamoto and P.A. Beck, Metall. Trans. 2 ( 1971 ) 569. [2] R.D. Shull, H. Okamoto and P.A. Beck, Solid State Commun. 20 (1976) 863. [ 3 ] P. Shukla and M. Wortis, Phys. Rev. B 21 (1980) 159. [4] J.S. Kouvel, J. Appl. Phys. 30 (1959) 313S. [5] M.J. Besnus, A. Herr and A.J. Meyer, J. Phys. F 5 (1975) 2138. [6] S. Takahashi, J. Magn. Magn. Mater. 54-56 (1986) 1065. [7] S. Takahashi and Y. Umakoshi, J. Phys. Condens. Matt. 3 (1991) 5805.