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Electrical resistivity of reentrant spin glass Fe91Zr9 under pressure
~
ELSEVIER
Journal of Magnetism and Magnetic Materials 196-197 (1999) 148-150
Journalof magnetism and magnetic J H materials
Electrical resistivity of reentrant spin glass Fe91Zr9 under pressure L. Fernfindez Barquin a'*, J.C. G6mez Sal a, R. Hauser b, E. Bauer b ~CTTIMAC, F. Ciencias, Universidad de Cantabria. Santander 39005. Spain blnstitut fur Experimentalphysik. Tech, Universit~t Wien. Wien 1040. Austria
Abstract The electrical resistivity of the reentrant spin glass Fe91Zr9 amorphous alloy has been studied from 10 K to RT between 1 bar and 13 kbar. Increasing pressure results in a decrease of the magnitude of resistivity and a extremely large shift of the minimum temperature (ATtain > 100 K). At 13 kbar, the resistivity shape is similar to that of amorphous Co-Zr (Co-rich) and Fe-B alloys, in which no spin glass state is present at low temperatures. The relationship between the Curie temperature and Tmi n shifts with pressure is discussed. :~'~ 1999 Elsevier Science B.V. All rights reserved. Keywords. Amorphous alloys; Spin glass; Pressure-electrical resistivity
The melt spinning technique allows to produce Fe-Zr amorphous alloys with high Fe-content (around 90%), which display extremely interesting magnetic-related properties. It is well known the existence of a reentrant spin glass state at low temperatures, wide hyperfine field distributions from Massbauer spectroscopy, decreasing magnetic moment and Tc with increasing Fe-content, Invar behaviour and electrical resistivity curves p(T) with minima at large temperatures, among other features [1-4]. Most of these phenomena are explained by the existence of a rather inhomogeneous magnetic and structural arrangement, probably formed during the casting process due to a competition among different Fe-structures. Recent studies on the thermal resistivity variation tried to explain at least qualitatively the existence of the rather large minima as a result of the interplay of several electronic scattering contributions [3,4]. From the phenomenological point of view, it seems reasonable to think of these alloys in the same terms as to Fe-based alloys
*Corresponding author. Tel.: + 34-942-201512; fax: + 34942-201402; e-mail: [email protected].
including Cr or Mn, where an inhomogeneous spin structure and the existence of numerous electronic scattering contributions have been reported [5]. Also, Shirakawa et al. [6] studied the pressure variation of p(T) of FegoZrlo, but constrained to the 140-300 K region. Here, it is shown the pressure variation of Fe91Zr9 over a larger temperature region (10 K-RT). The present sample has been taken from the same batch as the one reported in Refs. [3,4]. The ribbons were obtained by melt-spinning under Ar-atmosphere. X-ray diffraction was performed to check the amorphous state of the around 3 mm wide and 25 ~tm thick ribbons. Resistivity measurements were carried out using a standard four-probe set up using a liquid pressure cell up to 13 kbar. In the following, we will present and discuss on the variation with pressure of: (i) the absolute resistivity values, (ii) the minima temperatures and (iii) the general curve shape due to different scattering contributions. In Fig. 1, the p(T) variation of the sample is shown for different pressures. Three observations arc specially prominent: (i) the reduction of the resistivity magnitude with applied pressure; (ii) the existence of a large minimum which is progressively shifted down to lower temperatures with increasing pressure and, (iii) the global
0304-8853/99/$ - see front matter ~ 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 6 9 5 - 7
L. Fernandez Barquin et al. / Journal of Magnetism and Magnetic Materials 196-197 (1999) 148-150 I08
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150 T (K)
200
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•
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•
:
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0
2
4
6 8 10 Pressure (Kbar)
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6 8 10 Pressure (Kbar)
• 1'2
14
300
Fig. 1. Variation of the p(P,T) of Fe91Zrg. Train and T~ are marked with full and dashed arrows, respectively. Some data points and pressure runs have been dropped for clarity,
lid 150K 280 K
. . . . . . . .
12
Fig. 2. Relative variation of absolute value of resistivity with pressure. Data taken for characteristic temperatures at the RSG (20 K), FM (150 K) and PM (280 K) states.
variation of curve shape, with the appearance of supplementary low-temperature minima for the larger pressure measurements. The pressure reduction of resistivity is observed quite commonly in magnetic metallic glasses [7]. The relative variation of the resistivity (%) is different depending on the magnetic state of the sample: at T < Taso ~ 25 K (spin glass, RSG), TRSG< T < Tc = 210 K (Ferromagnetic, FM) and T > T~ (Paramagnetic, PM). In Fig. 2 these variations are presented at 20 K (RSG), 150 K (FM) and 280K (PM). The variations are larger at the lower temperatures (SG&FM). This agrees well with the results reported for Fe9oZrl0 [6], where (1/RXdR/dT) oc ~c, being ~c the compressibility, which seems to he more temperature dependent in the magnetic regimes (FM&RSG). The variation of Tmi. is plotted in Fig. 3. The temperature for the minima have been calculated from the T > 140 K minima points except for the curves at 10 and 13 kbar, in which two minima are taken into consideration. In the figure, we have also included data of FegoZrlo. The variations of both alloys are pretty close (in the common temperature range). In Ref. [6] this Tmi. variation is closely related to the To variation. The existing correlation allows to estimate the TriP) using dT¢dP in Ref. [8]: The Tc obtained from this estimation (Tall3 kbar) ~ 136 K) is marked in Fig. 1. In any case, from the high-pressure curve shapes, it turns out that apart from this T¢-Tmi, correlation, there might exist
Fig. 3. T,,i, variation of FegtZr 9 (dots) compared to FegoZrao (squares, from Ref. I-6]). Differencesare very slight when a similar temperature range is covered.
other effects giving rise to the commented additional subtle minimum (progressive disappearance of the large temperature minimum in favor of the onset of a minimum at lower T). Indeed, the curve at 13 kbar seems close to a typical low resistivity ferromagnetic amorphous alloy, in which quantum contributions only are observed at very low temperatures (below T < 20 K), being most of the p(T) caused by the existence of the electron-magnon and electron-phonon (usual extended Faber-Ziman-EFZ) scattering contributions [9]. More precisely, it is very similar to that of amorphous Co9oZrlo or Fe-B alloys, in which no reentrant spin glass state is found and usual ferromagnetic character persists down to low temperatures [10-12]. Very likely, the pressure affects the interatomic distances varying the magnitudes that drive the Stoner criterium for itinerant ferromagnetism. The exchange ho is expected to increase with pressure, contrary to N(Ev) [13]. Here the pressure appears to reduce the T¢ and hence N(EF) seems to be the most important parameter affecting the magnetic properties. Also, the applied pressure gives rise to a 'standard' amorphous ferromagnet resistivity behaviour; in such ferromagnetic alloys, the values of N(EF) are much lower than those for Fe-Zr alloys [10-12] confirming the reduction of N(EF) above derived from the Tc pressure variation. Regarding the variation of the low-temperature side (T < 70 K) of the curves, the increasing initial curvature could be not only a sign of a variation of the quantum scattering, but also an indication of an increasing homogeneity of the alloy with pressure, with the disappearance of any magnetic inhomogeneities-disordered spin structures, just similarly as what it happens with the addition of B in the Fe-Zr alloys [12]. The intermediate region between 100 and 200 K shows certain decrease of the resistivity, which could also be related to the magnetic effects explained above. Thus, a competition between the magnetic contributions from local spin-density fluctuation and magnon scatterings is expected [3,4], whereas the electron-phonon contribution should not affect significantly the shape of the curves, apart from slight variations in parameters such as kv and S(KF) present in the EFZ theory.
150
L. Ferngmdez Barquin et al. /Journal o['Magnetism and Magnetic Materials 196-197 (1999) 148-150
In conclusion, the m a i n effect of pressure is to modify the magnetic c h a r a c t e r of the alloy, which tends to behave as usual ferromagnetic a m o r p h o u s c o m p o u n d s characterized by a low N(Ev), as a result of a n h o m o g e nization of the structural a n d magnetic arrangements. This work has been partially C I C Y T - M A T 9 6 - 1 0 2 3 grant.
supported
References [1] D.H, Ryan et al., Phys. Rev. B 35 11987) 8630. [2] S.N. Kau] et al., Phys. Rev, B 45 (1992) 12343.
by the
[3] L. Fern/mdez Barquin et al.. J. Magn, Magn. Mater. 133 (1994) 82. [4] P.D. Babu et al., J. Magn. Magn. Mater. 140-144 (19951 295. [5] M. Olivier et al., Phys. Rev, B 35 (1987) 333. [6] K. Shirakawa et al., Phys. Lett. A 97 (1983) 213. [7] G. Fritsch et al., J. Magn. Magn. Mater. 37 (1983~ 30. [8] K. Shirakawa et al., Physica B 119 (19831 192. [9] g. Fernfindez Barquin et al., J. Appl. Phys. 68 11990) 4610. [10] Y. Obi et al., J. Appl. Phys. 53 (1982) 1826. [11] S.N. Kaul, Phys. Rev. B 27 (1983) 6923. [12] J.M. Barandiarfin et al., J. Phys.: Condens. Matter 9 (1997) 5671. [13] A. Hernandoet al., J. Magn. Magn. Mater. 174(1997) 181.
ELSEVIER
Journal of Magnetism and Magnetic Materials 196-197 (1999) 148-150
Journalof magnetism and magnetic J H materials
Electrical resistivity of reentrant spin glass Fe91Zr9 under pressure L. Fernfindez Barquin a'*, J.C. G6mez Sal a, R. Hauser b, E. Bauer b ~CTTIMAC, F. Ciencias, Universidad de Cantabria. Santander 39005. Spain blnstitut fur Experimentalphysik. Tech, Universit~t Wien. Wien 1040. Austria
Abstract The electrical resistivity of the reentrant spin glass Fe91Zr9 amorphous alloy has been studied from 10 K to RT between 1 bar and 13 kbar. Increasing pressure results in a decrease of the magnitude of resistivity and a extremely large shift of the minimum temperature (ATtain > 100 K). At 13 kbar, the resistivity shape is similar to that of amorphous Co-Zr (Co-rich) and Fe-B alloys, in which no spin glass state is present at low temperatures. The relationship between the Curie temperature and Tmi n shifts with pressure is discussed. :~'~ 1999 Elsevier Science B.V. All rights reserved. Keywords. Amorphous alloys; Spin glass; Pressure-electrical resistivity
The melt spinning technique allows to produce Fe-Zr amorphous alloys with high Fe-content (around 90%), which display extremely interesting magnetic-related properties. It is well known the existence of a reentrant spin glass state at low temperatures, wide hyperfine field distributions from Massbauer spectroscopy, decreasing magnetic moment and Tc with increasing Fe-content, Invar behaviour and electrical resistivity curves p(T) with minima at large temperatures, among other features [1-4]. Most of these phenomena are explained by the existence of a rather inhomogeneous magnetic and structural arrangement, probably formed during the casting process due to a competition among different Fe-structures. Recent studies on the thermal resistivity variation tried to explain at least qualitatively the existence of the rather large minima as a result of the interplay of several electronic scattering contributions [3,4]. From the phenomenological point of view, it seems reasonable to think of these alloys in the same terms as to Fe-based alloys
*Corresponding author. Tel.: + 34-942-201512; fax: + 34942-201402; e-mail: [email protected].
including Cr or Mn, where an inhomogeneous spin structure and the existence of numerous electronic scattering contributions have been reported [5]. Also, Shirakawa et al. [6] studied the pressure variation of p(T) of FegoZrlo, but constrained to the 140-300 K region. Here, it is shown the pressure variation of Fe91Zr9 over a larger temperature region (10 K-RT). The present sample has been taken from the same batch as the one reported in Refs. [3,4]. The ribbons were obtained by melt-spinning under Ar-atmosphere. X-ray diffraction was performed to check the amorphous state of the around 3 mm wide and 25 ~tm thick ribbons. Resistivity measurements were carried out using a standard four-probe set up using a liquid pressure cell up to 13 kbar. In the following, we will present and discuss on the variation with pressure of: (i) the absolute resistivity values, (ii) the minima temperatures and (iii) the general curve shape due to different scattering contributions. In Fig. 1, the p(T) variation of the sample is shown for different pressures. Three observations arc specially prominent: (i) the reduction of the resistivity magnitude with applied pressure; (ii) the existence of a large minimum which is progressively shifted down to lower temperatures with increasing pressure and, (iii) the global
0304-8853/99/$ - see front matter ~ 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 9 8 ) 0 0 6 9 5 - 7
L. Fernandez Barquin et al. / Journal of Magnetism and Magnetic Materials 196-197 (1999) 148-150 I08
0 ....
,
.2o1
I(~ 104
=
=_ 102
~,,~
°°OOo~~,~,;..... *, ,~,o,~
149
,
--e_ ~
30 ~ -40 [
- -o-.
II
°
-Sf)
100
: °0t
98
0
96
50
0
100
150 T (K)
200
250
•
t 8
20K
•
:
•
E
0
2
4
6 8 10 Pressure (Kbar)
2
4
6 8 10 Pressure (Kbar)
• 1'2
14
300
Fig. 1. Variation of the p(P,T) of Fe91Zrg. Train and T~ are marked with full and dashed arrows, respectively. Some data points and pressure runs have been dropped for clarity,
lid 150K 280 K
. . . . . . . .
12
Fig. 2. Relative variation of absolute value of resistivity with pressure. Data taken for characteristic temperatures at the RSG (20 K), FM (150 K) and PM (280 K) states.
variation of curve shape, with the appearance of supplementary low-temperature minima for the larger pressure measurements. The pressure reduction of resistivity is observed quite commonly in magnetic metallic glasses [7]. The relative variation of the resistivity (%) is different depending on the magnetic state of the sample: at T < Taso ~ 25 K (spin glass, RSG), TRSG< T < Tc = 210 K (Ferromagnetic, FM) and T > T~ (Paramagnetic, PM). In Fig. 2 these variations are presented at 20 K (RSG), 150 K (FM) and 280K (PM). The variations are larger at the lower temperatures (SG&FM). This agrees well with the results reported for Fe9oZrl0 [6], where (1/RXdR/dT) oc ~c, being ~c the compressibility, which seems to he more temperature dependent in the magnetic regimes (FM&RSG). The variation of Tmi. is plotted in Fig. 3. The temperature for the minima have been calculated from the T > 140 K minima points except for the curves at 10 and 13 kbar, in which two minima are taken into consideration. In the figure, we have also included data of FegoZrlo. The variations of both alloys are pretty close (in the common temperature range). In Ref. [6] this Tmi. variation is closely related to the To variation. The existing correlation allows to estimate the TriP) using dT¢dP in Ref. [8]: The Tc obtained from this estimation (Tall3 kbar) ~ 136 K) is marked in Fig. 1. In any case, from the high-pressure curve shapes, it turns out that apart from this T¢-Tmi, correlation, there might exist
Fig. 3. T,,i, variation of FegtZr 9 (dots) compared to FegoZrao (squares, from Ref. I-6]). Differencesare very slight when a similar temperature range is covered.
other effects giving rise to the commented additional subtle minimum (progressive disappearance of the large temperature minimum in favor of the onset of a minimum at lower T). Indeed, the curve at 13 kbar seems close to a typical low resistivity ferromagnetic amorphous alloy, in which quantum contributions only are observed at very low temperatures (below T < 20 K), being most of the p(T) caused by the existence of the electron-magnon and electron-phonon (usual extended Faber-Ziman-EFZ) scattering contributions [9]. More precisely, it is very similar to that of amorphous Co9oZrlo or Fe-B alloys, in which no reentrant spin glass state is found and usual ferromagnetic character persists down to low temperatures [10-12]. Very likely, the pressure affects the interatomic distances varying the magnitudes that drive the Stoner criterium for itinerant ferromagnetism. The exchange ho is expected to increase with pressure, contrary to N(Ev) [13]. Here the pressure appears to reduce the T¢ and hence N(EF) seems to be the most important parameter affecting the magnetic properties. Also, the applied pressure gives rise to a 'standard' amorphous ferromagnet resistivity behaviour; in such ferromagnetic alloys, the values of N(EF) are much lower than those for Fe-Zr alloys [10-12] confirming the reduction of N(EF) above derived from the Tc pressure variation. Regarding the variation of the low-temperature side (T < 70 K) of the curves, the increasing initial curvature could be not only a sign of a variation of the quantum scattering, but also an indication of an increasing homogeneity of the alloy with pressure, with the disappearance of any magnetic inhomogeneities-disordered spin structures, just similarly as what it happens with the addition of B in the Fe-Zr alloys [12]. The intermediate region between 100 and 200 K shows certain decrease of the resistivity, which could also be related to the magnetic effects explained above. Thus, a competition between the magnetic contributions from local spin-density fluctuation and magnon scatterings is expected [3,4], whereas the electron-phonon contribution should not affect significantly the shape of the curves, apart from slight variations in parameters such as kv and S(KF) present in the EFZ theory.
150
L. Ferngmdez Barquin et al. /Journal o['Magnetism and Magnetic Materials 196-197 (1999) 148-150
In conclusion, the m a i n effect of pressure is to modify the magnetic c h a r a c t e r of the alloy, which tends to behave as usual ferromagnetic a m o r p h o u s c o m p o u n d s characterized by a low N(Ev), as a result of a n h o m o g e nization of the structural a n d magnetic arrangements. This work has been partially C I C Y T - M A T 9 6 - 1 0 2 3 grant.
supported
References [1] D.H, Ryan et al., Phys. Rev. B 35 11987) 8630. [2] S.N. Kau] et al., Phys. Rev, B 45 (1992) 12343.
by the
[3] L. Fern/mdez Barquin et al.. J. Magn, Magn. Mater. 133 (1994) 82. [4] P.D. Babu et al., J. Magn. Magn. Mater. 140-144 (19951 295. [5] M. Olivier et al., Phys. Rev, B 35 (1987) 333. [6] K. Shirakawa et al., Phys. Lett. A 97 (1983) 213. [7] G. Fritsch et al., J. Magn. Magn. Mater. 37 (1983~ 30. [8] K. Shirakawa et al., Physica B 119 (19831 192. [9] g. Fernfindez Barquin et al., J. Appl. Phys. 68 11990) 4610. [10] Y. Obi et al., J. Appl. Phys. 53 (1982) 1826. [11] S.N. Kaul, Phys. Rev. B 27 (1983) 6923. [12] J.M. Barandiarfin et al., J. Phys.: Condens. Matter 9 (1997) 5671. [13] A. Hernandoet al., J. Magn. Magn. Mater. 174(1997) 181.