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Rapid solidification of Fe-Cr-Si-B alloys by melt spinning
Materials Science and Engineering A304–306 (2001) 1008–1010
Rapid solidification of Fe-Cr-Si-B alloys by melt spinning R. Yapp∗ , B.E. Watts, F. Leccabue Istituto MASPEC/CNR, Parco Area delle Scienze 37a, I-43010 Fontanini, Parma, Italy
Abstract Alloys in the series Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14) were prepared by rapid quenching from the melt, using the technique of melt spinning in a controlled argon atmosphere in order to produce amorphous ribbons. Mössbauer spectra, magnetic measurements and Curie temperature (TC ) measurements were performed. The effect of the substitution of Cr for Fe on TC , and magnetic properties was studied and, as expected, a significant decrease in TC was observed with increasing Cr content. Since, for these alloys, the crystallisation temperature, Tx is well above TC , they have potential uses in switching devices and temperature sensors. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Rapid quenching; Amorphous; FeCrSiB; Curie temperature
1. Introduction
2. Experimental
The melt spinning technique allows the rapid solidification of metallic alloys to produce amorphous or nanocrystalline materials. Amorphous Fe-based materials have good soft magnetic properties, and have been the subject of much scientific research over the past few decades. They are used in diverse applications, such as power devices, information handling technology and magnetic sensors [1,2]. For certain Fe-based amorphous alloys, the Curie temperature, TC , the temperature at which the material changes from being ferromagnetic to paramagnetic, may be changed by altering the composition of the alloy. Thus materials may be designed to have a particular TC , and by selecting a material with a known TC , it is possible to gauge when the material passes through this temperature by observing the magnetic behaviour. In alloys where TC is below the crystallisation temperature, Tx , the alloys have the potential to act as temperature switches or sensors. The substitution of Cr for Fe in FeSiB alloys is known to decrease the TC of the alloy [3,4]. This paper reports the results of the substitution of Cr for Fe in rapidly solidified Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14) alloys, with the aim of producing a material that could be utilised in a magnetic temperature sensor.
Alloys of the composition Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14, δx = 2 at.%) were prepared by melting pure constituent elements, either in an arc furnace or by use of RF induction melting in an argon atmosphere. There was typically a 0.1 wt.% loss on melting. The ingots were melted several times to ensure homogeneity, although the composition of the alloys after melting was not checked for the results presented here, as previous samples checked using a gravimetric method showed good compositional homogeneity and no significant change of composition on melting. Amorphous ribbons were produced by melt spinning the ingots onto a rotating copper wheel with a velocity of ∼40 m/s in a controlled atmosphere of argon. The same series of alloys was also planar flow cast (PFC) in order to provide wider specimens for the magnetic measurements. The resulting ribbons were ∼20 m thick and 1 mm wide in the case of melt spun ribbon, or up to 5 mm wide for PFC ribbon. The X-ray diffraction performed on all samples in the alloy series confirmed the amorphous nature of the ribbons. The Curie temperatures were determined from thermomagnetic analysis (TMA) with an in-house equipment using a heating rate of 20◦ C per minute, and by use of a DuPont differential scanning calorimeter (DSC), again using a heating rate of 20◦ C per minute. Mössbauer spectra of the Fe57 14.4 keV gamma radiation were recorded using a 20 mCiCo57 source in a Rh matrix with the spectrometer working at constant acceleration, and the absorber samples held at temperatures between room temperature and 180◦ C. Magnetic measurements were performed on planar flow cast ribbons that had been annealed in an argon atmosphere at 300◦ C for 1 h,
∗ Corresponding author. Tel.: +39-521-269229; fax: +39-521-269206. E-mail address: [email protected] (R. Yapp).
0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 7 4 2 - 1
R. Yapp et al. / Materials Science and Engineering A304–306 (2001) 1008–1010
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using an in-house hysteresis loop tracer at fields of 0.1–1 T, and with frequencies in the range of 50 Hz–10 kHz.
3. Results and discussion Fig. 1 shows the dependence of the TC on the composition of the alloy. As expected, a linear decrease in TC was observed with increasing at.% Cr, with T C = 367◦ C at x = 0 to T C = 30◦ C at x = 14. The TC decreased by ∼25◦ C for each at.% Cr present in the alloy, and this decrease may be attributed to the influence of the antiferromagnetically coupled Cr moments [5]. Both TC and Tx were also measured by differential scanning calorimeter for selected samples, and the TC was found to be in good agreement with that obtained by thermomagnetic analysis. The Tx of the samples was of the order of 500◦ C and thus well above the TC . The TC of the sample containing 10 at.% Cr was also determined using Mössbauer spectroscopy by measuring the dependence of the transmitted radiation on the sample temperature. A distinct change in transmitted radiation is observed at the temperature at which the hyperfine field disappears, and this critical temperature may be assumed to be the TC of the sample at zero magnetisation seen through the characteristic Mössbauer time window (∼10−7 s). Fig. 2 shows typical Mössbauer spectra for measurements taken above (Fig. 2a) and below (Fig. 2b) the TC , whilst in Fig. 3, the half width of the Mössbauer spectra as a function of the temperature is plotted. The TC estimated from this plot is usually taken to be the intersection point from the extrapolation of two lines drawn on the curve above and below TC . Thus, for this sample the TC determined by this method is of the order of 140–150◦ C, with the broadness of the transition
probably being due to the amorphous nature of the sample. This is some 10–20◦ C higher than that found by TMA and DSC for the same alloy, which was measured as 130◦ C by both methods, and the reason for this discrepancy is not completely clear. Low temperature annealing of this alloy has been shown [6] to cause an increase in TC of up to ∼150◦ C,
Fig. 1. TC as function of x, at.% Cr, for Fe80−x Crx Si10 B10 .
Fig. 3. Half height peak width vs. temperature trace for Fe70 Cr10 Si10 B10 .
Fig. 2. Characteristic Mössbauer spectra for Fe70 Cr10 Si10 B10 : (a) above and (b) below the TC .
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R. Yapp et al. / Materials Science and Engineering A304–306 (2001) 1008–1010
drop of approximately 90% in the values measured at x = 0 and x = 14. These trends are in agreement with results for Fe80 B20 -based Cr substituted alloys recorded in the literature [9].
4. Conclusions For the Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14) amorphous alloy system it was found that TC decreased with increasing Cr content, with a reduction of ∼25◦ C being observed for each at.% Cr substituted. Crystallisation temperatures were found to be of the order of 500◦ C. Measurements of Curie temperature by Mössbauer were found to be approximately 20◦ C higher than those found by TMA and DSC for the sample containing 10 at.% Cr. The reason for this difference is not yet clear. Magnetic hysteresis loops demonstrated that the substitution of Cr for Fe caused a notable decrease in saturation magnetisation, remanence and coercivity. Fig. 4. Typical MH loops measured at 100 Hz for Fe80−x Crx Si10 B10 samples with varying Cr content.
which is attributed to changes in the short range order. Given that for the Mössbauer data collection, the sample was held at the various measurement temperatures for several days, it is possible that these low temperature heat treatments may account for all or part of the difference. A discrepancy is also noted for polycrystalline PbFe12−x Crx O19 alloys [7] where it was found that for alloys with no Cr content the TC measured for both samples was equal, whilst when the amount of Cr present in the alloy increased, there was an growing discrepancy between the DSC and Mössbauer values of TC measured (∂T = 0 for x = 0, ∂T = 25◦ C for x = 6) which was attributed to spin–spin relaxation rates in the sample being above the characteristic Mössbauer time [8]. It is thus feasible that the Cr in the current alloy series may have a similar effect, and further studies are currently underway to investigate this in more depth. In Fig. 4, typical hysteresis loops measured at 100 Hz are presented for samples with varying Cr contents. It may be observed that the Cr has a significant effect on the form of the hysteresis loop, causing a decrease in coercivity, saturation magnetisation and remanence. Values of saturation magnetisation and remanence fell almost linearly, with a
Acknowledgements R. Yapp acknowledges the award of a Marie Curie Fellowship from the European Commission, contract number ERBFMBICT972516. The authors are grateful to G. Albanese and G. Galli of the Physics Department of the University of Parma, Italy, for Mössbauer spectroscopy measurements, and to E. Ferrara and colleagues at the Istituto Elettrotecnico Nazionale Galileo Ferraris, Turin, Italy, for assistance with MH hysteresis loop measurements. References [1] C.D. Graham, T. Egami, J. Magn. Magn. Mater. 15–18 (1980) 1325. [2] O.L. Sokol-Kutylovkij, Sens. Actuators A62 (1997) 496. [3] G. Vértesy, A. Lovas, J. Szöllösy, T. Tarnóczi, J. Magn. Magn. Mater. 102 (1991) 135. [4] J. Sun, H. Zhai, D. Qiu, H.Q. Wang, IEEE Trans. Mag. MAG-23 (1987) 2146. [5] T. Tarnóczi, A. Lovas, C. Kopasz, J. Mat. Sci. Eng. 97 (1988) 509. [6] R. Yapp, B.E. Watts, F. Leccabue, J. Magn. Magn. Mater. 215–216 (2000) 300. [7] G. Albanese, B.E. Watts, F. Leccabue, S. D´ıaz Castañón, J. Magn. Magn. Mater. 184 (1998) 337. [8] I.A. Campbell, Hyperfine Interactions 27 (1986) 15. [9] K. Hoselitz, J. Magn. Magn. Mater. 36 (1983) 39.
Rapid solidification of Fe-Cr-Si-B alloys by melt spinning R. Yapp∗ , B.E. Watts, F. Leccabue Istituto MASPEC/CNR, Parco Area delle Scienze 37a, I-43010 Fontanini, Parma, Italy
Abstract Alloys in the series Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14) were prepared by rapid quenching from the melt, using the technique of melt spinning in a controlled argon atmosphere in order to produce amorphous ribbons. Mössbauer spectra, magnetic measurements and Curie temperature (TC ) measurements were performed. The effect of the substitution of Cr for Fe on TC , and magnetic properties was studied and, as expected, a significant decrease in TC was observed with increasing Cr content. Since, for these alloys, the crystallisation temperature, Tx is well above TC , they have potential uses in switching devices and temperature sensors. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Rapid quenching; Amorphous; FeCrSiB; Curie temperature
1. Introduction
2. Experimental
The melt spinning technique allows the rapid solidification of metallic alloys to produce amorphous or nanocrystalline materials. Amorphous Fe-based materials have good soft magnetic properties, and have been the subject of much scientific research over the past few decades. They are used in diverse applications, such as power devices, information handling technology and magnetic sensors [1,2]. For certain Fe-based amorphous alloys, the Curie temperature, TC , the temperature at which the material changes from being ferromagnetic to paramagnetic, may be changed by altering the composition of the alloy. Thus materials may be designed to have a particular TC , and by selecting a material with a known TC , it is possible to gauge when the material passes through this temperature by observing the magnetic behaviour. In alloys where TC is below the crystallisation temperature, Tx , the alloys have the potential to act as temperature switches or sensors. The substitution of Cr for Fe in FeSiB alloys is known to decrease the TC of the alloy [3,4]. This paper reports the results of the substitution of Cr for Fe in rapidly solidified Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14) alloys, with the aim of producing a material that could be utilised in a magnetic temperature sensor.
Alloys of the composition Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14, δx = 2 at.%) were prepared by melting pure constituent elements, either in an arc furnace or by use of RF induction melting in an argon atmosphere. There was typically a 0.1 wt.% loss on melting. The ingots were melted several times to ensure homogeneity, although the composition of the alloys after melting was not checked for the results presented here, as previous samples checked using a gravimetric method showed good compositional homogeneity and no significant change of composition on melting. Amorphous ribbons were produced by melt spinning the ingots onto a rotating copper wheel with a velocity of ∼40 m/s in a controlled atmosphere of argon. The same series of alloys was also planar flow cast (PFC) in order to provide wider specimens for the magnetic measurements. The resulting ribbons were ∼20 m thick and 1 mm wide in the case of melt spun ribbon, or up to 5 mm wide for PFC ribbon. The X-ray diffraction performed on all samples in the alloy series confirmed the amorphous nature of the ribbons. The Curie temperatures were determined from thermomagnetic analysis (TMA) with an in-house equipment using a heating rate of 20◦ C per minute, and by use of a DuPont differential scanning calorimeter (DSC), again using a heating rate of 20◦ C per minute. Mössbauer spectra of the Fe57 14.4 keV gamma radiation were recorded using a 20 mCiCo57 source in a Rh matrix with the spectrometer working at constant acceleration, and the absorber samples held at temperatures between room temperature and 180◦ C. Magnetic measurements were performed on planar flow cast ribbons that had been annealed in an argon atmosphere at 300◦ C for 1 h,
∗ Corresponding author. Tel.: +39-521-269229; fax: +39-521-269206. E-mail address: [email protected] (R. Yapp).
0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 7 4 2 - 1
R. Yapp et al. / Materials Science and Engineering A304–306 (2001) 1008–1010
1009
using an in-house hysteresis loop tracer at fields of 0.1–1 T, and with frequencies in the range of 50 Hz–10 kHz.
3. Results and discussion Fig. 1 shows the dependence of the TC on the composition of the alloy. As expected, a linear decrease in TC was observed with increasing at.% Cr, with T C = 367◦ C at x = 0 to T C = 30◦ C at x = 14. The TC decreased by ∼25◦ C for each at.% Cr present in the alloy, and this decrease may be attributed to the influence of the antiferromagnetically coupled Cr moments [5]. Both TC and Tx were also measured by differential scanning calorimeter for selected samples, and the TC was found to be in good agreement with that obtained by thermomagnetic analysis. The Tx of the samples was of the order of 500◦ C and thus well above the TC . The TC of the sample containing 10 at.% Cr was also determined using Mössbauer spectroscopy by measuring the dependence of the transmitted radiation on the sample temperature. A distinct change in transmitted radiation is observed at the temperature at which the hyperfine field disappears, and this critical temperature may be assumed to be the TC of the sample at zero magnetisation seen through the characteristic Mössbauer time window (∼10−7 s). Fig. 2 shows typical Mössbauer spectra for measurements taken above (Fig. 2a) and below (Fig. 2b) the TC , whilst in Fig. 3, the half width of the Mössbauer spectra as a function of the temperature is plotted. The TC estimated from this plot is usually taken to be the intersection point from the extrapolation of two lines drawn on the curve above and below TC . Thus, for this sample the TC determined by this method is of the order of 140–150◦ C, with the broadness of the transition
probably being due to the amorphous nature of the sample. This is some 10–20◦ C higher than that found by TMA and DSC for the same alloy, which was measured as 130◦ C by both methods, and the reason for this discrepancy is not completely clear. Low temperature annealing of this alloy has been shown [6] to cause an increase in TC of up to ∼150◦ C,
Fig. 1. TC as function of x, at.% Cr, for Fe80−x Crx Si10 B10 .
Fig. 3. Half height peak width vs. temperature trace for Fe70 Cr10 Si10 B10 .
Fig. 2. Characteristic Mössbauer spectra for Fe70 Cr10 Si10 B10 : (a) above and (b) below the TC .
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R. Yapp et al. / Materials Science and Engineering A304–306 (2001) 1008–1010
drop of approximately 90% in the values measured at x = 0 and x = 14. These trends are in agreement with results for Fe80 B20 -based Cr substituted alloys recorded in the literature [9].
4. Conclusions For the Fe80−x Crx Si10 B10 (0 ≤ x ≤ 14) amorphous alloy system it was found that TC decreased with increasing Cr content, with a reduction of ∼25◦ C being observed for each at.% Cr substituted. Crystallisation temperatures were found to be of the order of 500◦ C. Measurements of Curie temperature by Mössbauer were found to be approximately 20◦ C higher than those found by TMA and DSC for the sample containing 10 at.% Cr. The reason for this difference is not yet clear. Magnetic hysteresis loops demonstrated that the substitution of Cr for Fe caused a notable decrease in saturation magnetisation, remanence and coercivity. Fig. 4. Typical MH loops measured at 100 Hz for Fe80−x Crx Si10 B10 samples with varying Cr content.
which is attributed to changes in the short range order. Given that for the Mössbauer data collection, the sample was held at the various measurement temperatures for several days, it is possible that these low temperature heat treatments may account for all or part of the difference. A discrepancy is also noted for polycrystalline PbFe12−x Crx O19 alloys [7] where it was found that for alloys with no Cr content the TC measured for both samples was equal, whilst when the amount of Cr present in the alloy increased, there was an growing discrepancy between the DSC and Mössbauer values of TC measured (∂T = 0 for x = 0, ∂T = 25◦ C for x = 6) which was attributed to spin–spin relaxation rates in the sample being above the characteristic Mössbauer time [8]. It is thus feasible that the Cr in the current alloy series may have a similar effect, and further studies are currently underway to investigate this in more depth. In Fig. 4, typical hysteresis loops measured at 100 Hz are presented for samples with varying Cr contents. It may be observed that the Cr has a significant effect on the form of the hysteresis loop, causing a decrease in coercivity, saturation magnetisation and remanence. Values of saturation magnetisation and remanence fell almost linearly, with a
Acknowledgements R. Yapp acknowledges the award of a Marie Curie Fellowship from the European Commission, contract number ERBFMBICT972516. The authors are grateful to G. Albanese and G. Galli of the Physics Department of the University of Parma, Italy, for Mössbauer spectroscopy measurements, and to E. Ferrara and colleagues at the Istituto Elettrotecnico Nazionale Galileo Ferraris, Turin, Italy, for assistance with MH hysteresis loop measurements. References [1] C.D. Graham, T. Egami, J. Magn. Magn. Mater. 15–18 (1980) 1325. [2] O.L. Sokol-Kutylovkij, Sens. Actuators A62 (1997) 496. [3] G. Vértesy, A. Lovas, J. Szöllösy, T. Tarnóczi, J. Magn. Magn. Mater. 102 (1991) 135. [4] J. Sun, H. Zhai, D. Qiu, H.Q. Wang, IEEE Trans. Mag. MAG-23 (1987) 2146. [5] T. Tarnóczi, A. Lovas, C. Kopasz, J. Mat. Sci. Eng. 97 (1988) 509. [6] R. Yapp, B.E. Watts, F. Leccabue, J. Magn. Magn. Mater. 215–216 (2000) 300. [7] G. Albanese, B.E. Watts, F. Leccabue, S. D´ıaz Castañón, J. Magn. Magn. Mater. 184 (1998) 337. [8] I.A. Campbell, Hyperfine Interactions 27 (1986) 15. [9] K. Hoselitz, J. Magn. Magn. Mater. 36 (1983) 39.