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Characterisation of amorphous Fe–Cr–Si–B alloys
Journal of Magnetism and Magnetic Materials 215}216 (2000) 300}302
Characterisation of amorphous Fe}Cr}Si}B alloys R. Yapp*, B.E. Watts, F. Leccabue Istituto MASPEC/CNR, Parco Area delle Scienze 37a, I-43010 Fontanini, Parma, Italy
Abstract The Fe } Cr Si B amorphous alloy system has been investigated for values of x between 0 and 14. The V V substitution of Cr for Fe caused a decrease in the Curie temperature, ¹ , of the alloy. Low-temperature annealing was ! found to increase ¹ by up to 163C. Magnetic measurements were also performed on selected alloys. This series of alloys, ! which have ¹ markedly below the crystallisation temperature, have potential to be used in magnetic temperature ! sensors. 2000 Elsevier Science B.V. All rights reserved. Keywords: Amorphous; Melt spin; Curie temperature
1. Introduction Amorphous Fe-based materials produced by the melt spinning technique have been the subject of much scienti"c research over the past few decades, due to their combination of high permeability, good mechanical properties, low hysteresis loss and low coercive force. They are used in diverse applications, including power devices, information handling and magnetic sensors [1,2]. Current research on amorphous materials for sensors is focusing on reliable higher-accuracy, lower-cost sensors, using both new and existing materials and technologies [3,4]. By altering the composition of certain Fe-based amorphous alloys, the Curie temperature, ¹ , the tem! perature at which the material changes from being ferromagnetic to paramagnetic, may be altered. Thus, materials may be designed to have a particular ¹ , and ! by selecting a material with a known Curie temperature, it is possible to gauge when the material passes through this temperature by observing the magnetic behaviour. In alloys where ¹ is below the crystallisation temperature, ! ¹ , the alloys have the potential to act as temperature V switches or sensors.
* Corresponding author. Tel.: #39-0521-269229; fax: #390521-269206. E-mail address: [email protected] (R. Yapp).
The substitution of Cr for Fe in FeSiB alloys is known to decrease the Curie temperature of the alloy [5}9]. This paper reports the results of the substitution of Cr for Fe in the alloy series Fe } Cr Si B , (x"0}14), with the V V aim of producing a material that could be utilised in a magnetic temperature sensor.
2. Experimental Alloys in the series Fe } Cr Si B (x"0}14) V V were prepared by melting pure constituent elements in an argon atmosphere, and subsequent melt spinning. The metallic ribbons were found to be amorphous by X-ray di!raction. The Curie temperatures were determined from thermomagnetic analysis using inhouse equipment, and by use of a dupont di!erential scanning calorimeter. Magnetic measurements were performed using an in-house hysteresis loop tracer, at "elds of 0.5}1 T, and with frequencies in the range of 50}10 kHz.
3. Results and discussion Curie temperature was determined from the thermomagnetic analysis curves for each of the samples, and con"rmed for selected samples by DSC measurements. As can be seen from Fig. 1 the dependence of Curie temperature on the composition was found to decrease
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 1 3 9 - 6
R. Yapp et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 300}302
301
relaxation of quenched-in stresses, as a result of modi"cations in the short-range order (SRO) [5,6,10]. The Curie temperature may be increased by up to 15% with lowtemperature annealing, of which approximately 2% is reported to be reversible [11]. Fig. 2 shows that for the Fe Cr Si B alloy, annealing at 2003C had very little e!ect on the ¹ , whilst annealing at 4003C for 3 h ! gave a ¹ some 163C higher than that observed for the ! as-cast ribbon of the same composition. It should be mentioned that prolonged low-temperature annealing may give greater ¹ enhancement, although these di!er! ences can be di$cult to detect, as the measurement of ¹ requires heating through the Curie transition [11]. ! Preliminary magnetic measurements were made on the amorphous ribbons, and typical hysteresis loops for Fe Cr Si B before and after heat treatment can be seen in Fig. 3. From this "gure it may be observed that the heat treatment increases the remanence by &50% Fig. 1. Curie temperature as a function of x for Fe } Cr Si B . The dotted line serves as a guide to the eye. V V
linearly with increasing Cr% for values of x between 0 and 14. A decrease in Curie temperature of&253C was observed for each atomic %Cr present in the alloy. The crystallisation temperature of the alloys was also measured for selected samples by DSC, and was found to be of the order of 5003C and thus well above the Curie temperature. As the range of Curie temperatures of interest in this study was 100}1503C, it was decided in the "rst instance to investigate further the properties of the Fe Cr Si B alloy, which had a ¹ of 1303C. ! As-cast amorphous ribbons tend to be structurally inhomogeneous, and thus, annealing below ¹ allows the V
Fig. 2. E!ect of annealing time and temperature on the Curie temperature of Fe Cr Si B amorphous ribbons. The dot ted lines serve as a guide to the eye.
Fig. 3. Typical hysteresis loops measured at a "eld of 0.5 T and a frequency of 1 kHz for a Fe Cr Si B ribbon: (a) as cast and (b) after heat treatment at 3003C for 1 h in a magnetic "eld of 4800 A/m.
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R. Yapp et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 300}302
ing Cr content, with a decrease of &253C being observed for each atomic %Cr substituted. Low-temperature annealing of the as-cast ribbon caused slight increases in the Curie temperature. Magnetic measurements made on Fe Cr Si B ribbons showed that after heat treatment the ribbon had a signi"cantly higher remanence and permeability, and a lower coercive "eld and energy loss. Acknowledgements R. Yapp acknowledges "nancial support from the EC under the TMR Marie Curie programme, Contract no. ERBFMBICT972516. The authors are grateful to E. Ferrara and colleagues at the Istituto Elettrotecnico Nazionale Galileo Ferraris, Turin, Italy, for assistance with hysteresis loop measurements. Fig. 4. Energy loss as a function of frequency for Fe Cr Si B ribbon as cast and after a heat treatment at 3003C for 1 h in a magnetic "eld of 4800 A/m. The dotted lines serve as a guide to the eye.
whilst reducing the coercivity by&50%. The energy loss also decreased as a result of the heat treatment, as shown in Fig. 4. These changes may be accounted for on the basis of the microstructural changes in the SRO that occur as a result of the low-temperature annealing. In addition, some initial measurements were made on as-cast Fe Cr Si B amorphous ribbons, which in dicated that these ribbons had a remanence and initial permeability more than double that of the Fe Cr Si B ribbons. A more thorough study of the amorphous Fe } Cr Si B (x"0}14) system is cur V V rently in progress to investigate the e!ects of the Cr substitution. 4. Conclusions For the Fe } Cr Si B (x"0}14) amorphous V V alloy system it was found that ¹ decreased with increas!
References [1] C.D. Graham, T. Egami, J. Magn. Magn. Mater. 15}18 (1980) 1325. [2] O.L. Sokol-Kutylovkij, Sensors Actuators A 62 (1997) 496. [3] K. Mohri, T. Uchiyama, L.V. Panina, Sensors Actuators A 59 (1997) 1. [4] T. Meydan, J. Magn. Magn. Mater. 133 (1994) 525. [5] G. VeH rtesy, A. Lovas, J. SzoK lloK sy, T. TarnoH czi, J. Magn. Magn. Mater. 102 (1991) 135. [6] J. Sun, H. Zhai, D. Qiu, H.Q. Wang, IEEE Trans. Magn. MAG-23 (1987) 2146. [7] G.C. Hadjipanayis, E.J. Yadlowsky, S.H. Wollins, D.J. Sellmyer, J. Appl. Phys. 53 (1982) 2270. [8] S. Ishio, M. Takahashi, J. Magn. Magn. Mater. 50 (1985) 93. [9] B. Lin, G.B. Yang, R. Wang, J. Non-Cryst. Solids 88 (1986) 323. [10] A. Lovas, ED . Kisdi-KoszoH , L. Potocky, L. NovaH k, J. Mater. Sci. 22 (1987) 1535. [11] A.L. Greer, in: H.H. Liebermann (Ed.), Rapidly Solidi"ed Alloys, Vol 3, Marcel Dekker, New York, 1993, p. 269.
Characterisation of amorphous Fe}Cr}Si}B alloys R. Yapp*, B.E. Watts, F. Leccabue Istituto MASPEC/CNR, Parco Area delle Scienze 37a, I-43010 Fontanini, Parma, Italy
Abstract The Fe } Cr Si B amorphous alloy system has been investigated for values of x between 0 and 14. The V V substitution of Cr for Fe caused a decrease in the Curie temperature, ¹ , of the alloy. Low-temperature annealing was ! found to increase ¹ by up to 163C. Magnetic measurements were also performed on selected alloys. This series of alloys, ! which have ¹ markedly below the crystallisation temperature, have potential to be used in magnetic temperature ! sensors. 2000 Elsevier Science B.V. All rights reserved. Keywords: Amorphous; Melt spin; Curie temperature
1. Introduction Amorphous Fe-based materials produced by the melt spinning technique have been the subject of much scienti"c research over the past few decades, due to their combination of high permeability, good mechanical properties, low hysteresis loss and low coercive force. They are used in diverse applications, including power devices, information handling and magnetic sensors [1,2]. Current research on amorphous materials for sensors is focusing on reliable higher-accuracy, lower-cost sensors, using both new and existing materials and technologies [3,4]. By altering the composition of certain Fe-based amorphous alloys, the Curie temperature, ¹ , the tem! perature at which the material changes from being ferromagnetic to paramagnetic, may be altered. Thus, materials may be designed to have a particular ¹ , and ! by selecting a material with a known Curie temperature, it is possible to gauge when the material passes through this temperature by observing the magnetic behaviour. In alloys where ¹ is below the crystallisation temperature, ! ¹ , the alloys have the potential to act as temperature V switches or sensors.
* Corresponding author. Tel.: #39-0521-269229; fax: #390521-269206. E-mail address: [email protected] (R. Yapp).
The substitution of Cr for Fe in FeSiB alloys is known to decrease the Curie temperature of the alloy [5}9]. This paper reports the results of the substitution of Cr for Fe in the alloy series Fe } Cr Si B , (x"0}14), with the V V aim of producing a material that could be utilised in a magnetic temperature sensor.
2. Experimental Alloys in the series Fe } Cr Si B (x"0}14) V V were prepared by melting pure constituent elements in an argon atmosphere, and subsequent melt spinning. The metallic ribbons were found to be amorphous by X-ray di!raction. The Curie temperatures were determined from thermomagnetic analysis using inhouse equipment, and by use of a dupont di!erential scanning calorimeter. Magnetic measurements were performed using an in-house hysteresis loop tracer, at "elds of 0.5}1 T, and with frequencies in the range of 50}10 kHz.
3. Results and discussion Curie temperature was determined from the thermomagnetic analysis curves for each of the samples, and con"rmed for selected samples by DSC measurements. As can be seen from Fig. 1 the dependence of Curie temperature on the composition was found to decrease
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 1 3 9 - 6
R. Yapp et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 300}302
301
relaxation of quenched-in stresses, as a result of modi"cations in the short-range order (SRO) [5,6,10]. The Curie temperature may be increased by up to 15% with lowtemperature annealing, of which approximately 2% is reported to be reversible [11]. Fig. 2 shows that for the Fe Cr Si B alloy, annealing at 2003C had very little e!ect on the ¹ , whilst annealing at 4003C for 3 h ! gave a ¹ some 163C higher than that observed for the ! as-cast ribbon of the same composition. It should be mentioned that prolonged low-temperature annealing may give greater ¹ enhancement, although these di!er! ences can be di$cult to detect, as the measurement of ¹ requires heating through the Curie transition [11]. ! Preliminary magnetic measurements were made on the amorphous ribbons, and typical hysteresis loops for Fe Cr Si B before and after heat treatment can be seen in Fig. 3. From this "gure it may be observed that the heat treatment increases the remanence by &50% Fig. 1. Curie temperature as a function of x for Fe } Cr Si B . The dotted line serves as a guide to the eye. V V
linearly with increasing Cr% for values of x between 0 and 14. A decrease in Curie temperature of&253C was observed for each atomic %Cr present in the alloy. The crystallisation temperature of the alloys was also measured for selected samples by DSC, and was found to be of the order of 5003C and thus well above the Curie temperature. As the range of Curie temperatures of interest in this study was 100}1503C, it was decided in the "rst instance to investigate further the properties of the Fe Cr Si B alloy, which had a ¹ of 1303C. ! As-cast amorphous ribbons tend to be structurally inhomogeneous, and thus, annealing below ¹ allows the V
Fig. 2. E!ect of annealing time and temperature on the Curie temperature of Fe Cr Si B amorphous ribbons. The dot ted lines serve as a guide to the eye.
Fig. 3. Typical hysteresis loops measured at a "eld of 0.5 T and a frequency of 1 kHz for a Fe Cr Si B ribbon: (a) as cast and (b) after heat treatment at 3003C for 1 h in a magnetic "eld of 4800 A/m.
302
R. Yapp et al. / Journal of Magnetism and Magnetic Materials 215}216 (2000) 300}302
ing Cr content, with a decrease of &253C being observed for each atomic %Cr substituted. Low-temperature annealing of the as-cast ribbon caused slight increases in the Curie temperature. Magnetic measurements made on Fe Cr Si B ribbons showed that after heat treatment the ribbon had a signi"cantly higher remanence and permeability, and a lower coercive "eld and energy loss. Acknowledgements R. Yapp acknowledges "nancial support from the EC under the TMR Marie Curie programme, Contract no. ERBFMBICT972516. The authors are grateful to E. Ferrara and colleagues at the Istituto Elettrotecnico Nazionale Galileo Ferraris, Turin, Italy, for assistance with hysteresis loop measurements. Fig. 4. Energy loss as a function of frequency for Fe Cr Si B ribbon as cast and after a heat treatment at 3003C for 1 h in a magnetic "eld of 4800 A/m. The dotted lines serve as a guide to the eye.
whilst reducing the coercivity by&50%. The energy loss also decreased as a result of the heat treatment, as shown in Fig. 4. These changes may be accounted for on the basis of the microstructural changes in the SRO that occur as a result of the low-temperature annealing. In addition, some initial measurements were made on as-cast Fe Cr Si B amorphous ribbons, which in dicated that these ribbons had a remanence and initial permeability more than double that of the Fe Cr Si B ribbons. A more thorough study of the amorphous Fe } Cr Si B (x"0}14) system is cur V V rently in progress to investigate the e!ects of the Cr substitution. 4. Conclusions For the Fe } Cr Si B (x"0}14) amorphous V V alloy system it was found that ¹ decreased with increas!
References [1] C.D. Graham, T. Egami, J. Magn. Magn. Mater. 15}18 (1980) 1325. [2] O.L. Sokol-Kutylovkij, Sensors Actuators A 62 (1997) 496. [3] K. Mohri, T. Uchiyama, L.V. Panina, Sensors Actuators A 59 (1997) 1. [4] T. Meydan, J. Magn. Magn. Mater. 133 (1994) 525. [5] G. VeH rtesy, A. Lovas, J. SzoK lloK sy, T. TarnoH czi, J. Magn. Magn. Mater. 102 (1991) 135. [6] J. Sun, H. Zhai, D. Qiu, H.Q. Wang, IEEE Trans. Magn. MAG-23 (1987) 2146. [7] G.C. Hadjipanayis, E.J. Yadlowsky, S.H. Wollins, D.J. Sellmyer, J. Appl. Phys. 53 (1982) 2270. [8] S. Ishio, M. Takahashi, J. Magn. Magn. Mater. 50 (1985) 93. [9] B. Lin, G.B. Yang, R. Wang, J. Non-Cryst. Solids 88 (1986) 323. [10] A. Lovas, ED . Kisdi-KoszoH , L. Potocky, L. NovaH k, J. Mater. Sci. 22 (1987) 1535. [11] A.L. Greer, in: H.H. Liebermann (Ed.), Rapidly Solidi"ed Alloys, Vol 3, Marcel Dekker, New York, 1993, p. 269.