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Magnetostriction of a Fe83Ga17 single crystal slightly doped with Tb
Scripta Materialia 114 (2016) 9–12
Contents lists available at ScienceDirect
Scripta Materialia journal homepage: www.elsevier.com/locate/scriptamat
Regular Article
Magnetostriction of a Fe83Ga17 single crystal slightly doped with Tb Chongzheng Meng, Chengbao Jiang ⁎ Key Laboratory of Aerospace Materials and Performance, Ministry of Education, School of Materials Science and Engineering, Beihang University, Beijing 100191, PR China
a r t i c l e
i n f o
Article history: Received 12 October 2015 Received in revised form 17 November 2015 Accepted 19 November 2015 Available online xxxx Keywords: Magnetostriction FeGaTb single crystal Sub-rapid directional solidification
a b s t r a c t A novel strategy of sub-rapid directional solidification is developed for preparing doped FeGa single crystals. Crystals of nominal composition Fe83Ga17Tbx (x = 0, 0.05) have been grown with [100] preferred orientation at a high growth rate of 3000 mm/h. Using this method, trace amounts of normally-insoluble Tb can be incorporated into the A2 Fe83Ga17 matrix. A large magnetostriction (λ100) of 310 ppm is achieved in the [100] oriented Fe83Ga17Tb0.05 single crystal, ~50% higher than that of a similar undoped crystal. © 2015 Elsevier B.V. All rights reserved.
The past few decades have witnessed extensive applications of magnetostrictive materials in different fields such as sensors, actuators and transducers [1,2]. The giant room-temperature magnetostriction of Terfenol-D (Tb1 − xDyxFe2) alloys has been widely used in these fields. However, Terfenol-D is limited by its mechanical brittleness, heavy use of rare earth elements and high magnetic saturation field [3]. Galfenol (Fe1 − xGax) alloys have the advantages of excellent ductility, low cost and low magnetic saturation field [4]. Magnetostriction or iron is enhanced tenfold when a fraction of the iron atoms are replaced by nonmagnetic Ga [5–8], although it is still much lower than that of Terfenol-D. Great efforts have been made to further improve the magnetostriction by adding 3d and 4d transition elements such as Ni, V, Cr, Mn, Co, Mo, and Rh [9–12], or interstitial elements such as C, B and N [13–15]. Despite all that, there was no significant enhancement in the magnetostriction. However, it was recently reported that the magnetostriction of Fe83Ga17 alloys could be remarkably increased by melt spinning with small amount of rare earth elements such as Tb, Dy and Ce [16–18], although the perpendicularly grown grains in the meltspun ribbons make it very difficult to measure the magnetostriction directly. Moreover, due to the large demagnetizing field, the shape anisotropy of the ribbons also leads to a high magnetic saturation field. Enhanced magnetostriction with lower applied field is expected in bulk FeGa slightly doped with rare earth elements, but it is hard to obtain such materials by conventional methods. Very recently, bulk Fe83Ga17Tbx has been prepared by a directional casting process and magnetostriction of up to 160 ppm was obtained in polycrystalline Fe83Ga17Tb0.2 alloys [19,20]. However, the relatively slow cooling rate limits the solid solubility of Tb in the A2 matrix of
⁎ Corresponding author. E-mail address: [email protected] (C. Jiang).
http://dx.doi.org/10.1016/j.scriptamat.2015.11.022 1359-6462/© 2015 Elsevier B.V. All rights reserved.
the FeGa alloy, and a sound magnetostriction could not be obtained by this method. Therefore, a novel strategy combining rapid solidification with directional solidification, is urgently required to achieve magnetostriction in Tb-doped Fe83Ga17 crystals. In this report, we develop a sub-rapid directional solidification procedure. [100] oriented Fe 83 Ga 17 single crystals slightly doped with Tb have been prepared, and their magnetostriction (λ 100 ) of up to 310 ppm is approximately 50% higher than that of undoped Fe83Ga17 crystals, and almost twice as high as previously reported for Fe83Ga17Tb0.2 prepared by directional casting [19]. The nominal Fe83Ga17Tbx (x = 0, 0.05) master alloys were prepared by arc melting from high purity starting elements Fe, Ga and Tb (99.99%). Each ingot was re-melted four times under an argon atmosphere and cast in a chilled copper mold to obtain master rods. The crystals were grown in a sub-rapid directional solidification furnace. Master rods were first entirely melted and then moved downwards into cooling medium at velocities of 1000 mm/h, 3000 mm/h or 6000 mm/h. Afterwards, the directional microstructure and the magnetostriction of the polycrystalline specimens were measured. Following that, x = 0.05 Tb-doped Fe83Ga17 and x = 0 undoped Fe83Ga17 single crystals were grown at a velocity of 3000 mm/h based on a [100] oriented Fe83Ga17 seed crystal as shown in Fig. 1. The crystals were then cut into sheets 3 mm × 4 mm × 1.3 mm with six [100] faces. The crystallographic structure was identified by X-ray diffraction (XRD, D/MAX 2200 PC) with CuKα radiation (λ = 154.18 pm) and scanning speed of 6°/min. The microscopic morphology of the crystals was determined by using a JEOL JXA8100 electron probe micro-analyzer (EPMA). The preferred orientation of the single crystals was determined by the Lauë back-reflection X-ray technique. Magnetostriction was measured by the standard strain gauge method, and magnetization hysteresis loops (M–H) were measured with a Quantum Design physical property measurement system (PPMS-9).
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C. Meng, C. Jiang / Scripta Materialia 114 (2016) 9–12
Fig. 1. Schematic illustration of sub-rapid directional solidification equipment.
It has been found that rapid solidification (melt spinning) can be used to prepare rare-earth doped FeGa solid solutions, resulting in a significant increase of magnetostriction [16–18]. It has also been proved that the directional solidification method can enhance the magnetostriction of FeGa alloys by realizing [100] orientation which has the highest value of anisotropic magnetostriction [6]. In order to incorporate the advantages of both rapid solidification and directional solidification concurrently, an optimal cooling rate (R = GL × V) is required, where GL is the liquid temperature gradient in front of the solid–liquid interface and V is the growth velocity. This can be realized with a large GL and V. We develop a novel strategy to achieve sub-rapid solidification, as shown in Fig. 1. In this equipment, high-frequency induction
coils and graphite sleeves are employed to melt the master rods. The liquid metal cooling medium (Ga–In) combined with a floating ceramic baffle (BN) was adopted in order to achieve large GL; V can be manipulated over a range of 1000–10,000 mm/h. Fig. 2(a) shows the granular morphology of polycrystalline Fe 83 Ga 17 Tb 0.05 in longitudinal sections of specimens prepared at different velocities. Columnar grains can be clearly observed along the growth direction in the 1000 mm/h and 3000 mm/h specimens, while lateral grains are found in the 6000 mm/h specimen. It appears that a growth velocity less than 3000 mm/h is beneficial for directional solidification. Furthermore, back-scattered electron (BSE) imaging has been employed to analyze the phase composition in Fe83Ga17Tb0.05 specimens. In Fig. 2(b), there are obvious bright spheres and rods distributed in a dark background in the 1000 mm/h specimen, suggesting that a second phase precipitates from the matrix along grain boundaries. The 3000 mm/h and 6000 mm/h specimens observed are single phase. Energy-dispersive X-ray spectroscopy (EDS) analysis confirms that the precipitates in the 1000 mm/h specimen are Tb-rich, possessing the rhombohedral Th2Zn17 structure (2:17R), consistent with our previous work [21]. This indicates that the solid solution of a trace amount of Tb can be achieved at a growth velocity of 3000 mm/h or more. Fig. 2(c) shows the XRD patterns of Fe83Ga17Tb0.05 specimens prepared at 1000 mm/h, 3000 mm/h and 6000 mm/h. All diffraction peaks are indexed as (110), (200) and (211) on the body-centered cubic (bcc) structure, demonstrating that the matrix of all the Tb-doped Fe83Ga17 alloys possesses the same bcc structure as the binary Fe83Ga17 alloy. Meanwhile, the intensity of the (200) diffraction peak increases with growth velocities up to a maximum at 3000 mm/h, suggesting that this velocity is beneficial for [100] preferred oriented growth. The magnetostriction of a Fe83Ga17Tb0.05 specimen (Ф 7 mm × 20 mm) is summarized in Fig. 2(d). With the increase of growth velocity, the magnetostriction changes significantly, to a maximum of 200 ppm at a growth velocity of 3000 mm/h, which can be attributed to the [100] orientation and the solid solution of Tb. Therefore, rapid solidification and directional solidification are concurrently achieved at 3000 mm/h in a sub-rapid directional solidification process. The solid solution of Tb was suppressed below a velocity of 3000 mm/h, whereas directional growth was impeded above a velocity of 3000 mm/h. Thus, we
Fig. 2. Characterization of Fe83Ga17Tb0.05 crystals prepared at different growth velocities of 1000 mm/h, 3000 mm/h or 6000 mm/h: (a) optical metallographic graphs of Fe83Ga17Tb0.05 crystals; (b) BSE images of the Fe83Ga17Tb0.05 crystals; (c) XRD patterns of Fe83Ga17Tb0.05 crystals; (d) magnetostriction of Fe83Ga17Tb0.05 crystals.
C. Meng, C. Jiang / Scripta Materialia 114 (2016) 9–12
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Fig. 3. (a) XRD pattern of a Fe83Ga17Tb0.05 single crystal (Inset: Lauë spots of the single crystal); (b) magnetostriction of the Fe83Ga17Tb0.05 single crystal, where curve A is the measured value and curve B is the calculated value without demagnetizing field (Inset: the magnetization hysteresis loops in first quadrant).
successfully prepared Fe83Ga17Tb0.05 polycrystals, where [100] orientation and large magnetostriction are achieved, which provide a basis for then preparing large Tb doped Fe83Ga17 single crystals. For Fe83Ga17Tb0.05 single crystal preparation, we used a [100] oriented Fe83 Ga 17 single crystal as a seed, to grow a [100] oriented Fe 83Ga 17 Tb0.05 single crystal at 3000 mm/h. Fig. 3(a) shows the XRD pattern of the as-prepared Fe83Ga17Tb0.05 single crystal. There is only one sharp (200) bcc diffraction peak near 64°, indicating the single crystal nature of the FeGa alloy. The orientation is confirmed by X-ray Lauë back-reflection. From the inset in Fig. 3(a), clear and perfect Lauë spots, as well as four-fold symmetry can be observed, confirming that the single crystal is in the [100] orientation. Fig. 3(b) shows the measured magnetostriction of the Fe83Ga17Tb0.05 single crystal (curve A); a magnetostriction of 310 ppm is achieved along the [100] direction. The slight addition of Tb considerably enhances the magnetostriction of FeGa. It can be seen from the magnetization curve (Fig. 3(b) inset) that the saturation magnetization of the Fe 83 Ga 17 Tb 0.05 single crystal is approximately 18 kOe and the magnetic saturation field is near 2.7 kOe. The demagnetizing factor in the longitudinal dimension N is about 0.15. Curve B shows the calculated magnetostriction without the demagnetizing field, and the effective saturation field is calculated to be nearly 300 Oe, which is in accordance with a previous report in undoped Fe83Ga17 [6]. In order to investigate the solid solubility of Terbium, step-scanned XRD was used to measure the (200) diffraction peak patterns of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals at 2°/min, as shown in Fig. 4(a). The (200) diffraction peak of Fe83Ga17Tb0.05 shows a clear broadening and shift to lower angles compared to that of the Fe83Ga17 crystal.
The (200) diffraction peaks of the Fe83Ga17Tb0.05 and Fe83Ga17 crystals at 63.88° and 63.99° correspond to lattice constants a0 of 291.1 pm and 290.6 pm, respectively. It is reasonable to assume that lattice expansion causes the movement of the diffraction peak, implying that Tb dissolved in the matrix, as expected. Additionally, the (200) peak broadens, which can be attributed to microstrain in the matrix, also confirming the solid solution of Tb. The magnetostriction of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals is compared in Fig. 4(b); a λ100 of 195 ppm is measured in the Fe83Ga17 single crystal, similar to a previous report [6]. The magnetostriction of the Fe83Ga17Tb0.05 single crystal is nearly 1.5 times greater. We conclude that the solid solution of terbium increases the magnetostriction significantly. In conclusion, a sub-rapid directional solidification strategy has been developed to achieve rapid and directional solidification simultaneously. Fe83Ga17 single crystals with [100] orientation were prepared with trace amounts of dissolved terbium. The nominal Fe83Ga17Tb0.05 single crystal exhibits a magnetostriction (λ100) of 310 ppm, which is 50% higher than that of the undoped Fe83Ga17 single crystal. Our work illustrates a promising approach to preparing other advanced structural and functional materials which contains trace quantities of insoluble dopants. Acknowledgment The authors are grateful to Professor J. M. D. Coey for fruitful discussion and revision of manuscript. This work was supported by the National Natural Science Foundation of China (NSFC) under Grant No. 51331001, and the National Basic Research Program of China (973 Program) under Grant No. 2012CB619404.
Fig. 4. (a) Step-scanned XRD patterns of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals; (b) magnetostriction of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals.
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References [1] J. Atulasimha, A.B. Flatau, E. Summers, Smart Mater. Struct. 16 (2007) 1265–1276. [2] J.M.D. Coey, Magnetism and Magnetic Materials, Cambridge University Press, New York, 2010 1. [3] A.E. Clark, Ferromagnetic Materials Vol. 1, North-Holland, Amsterdam, 1980 531. [4] H. Wang, Y.N. Zhang, T. Yang, Z.D. Zhang, L.Z. Sun, R.Q. Wu, Appl. Phys. Lett. 97 (262505) (2010) 1–4. [5] E.M. Summers, T.A. Lograsso, M. Wun-Fogle, J. Mater. Sci. 42 (2007) 9582–9594. [6] H.D. Chopra, M. Wuttig, Nature 521 (2015) 340–351. [7] A.E. Clark, J.B. Restorff, M. Wun-Fogle, T.A. Lograsso, D.L. Schlagel, IEEE Trans. Magn. 36 (2000) 3238–3240. [8] J.B. Restorff, M. Wun-Fogle, K.B. Hathaway, A.E. Clark, T.A. Lograsso, G. Petculescu, J. Appl. Phys. 111 (2012) 1–12, 023905. [9] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, G. Petculescu, J. Appl. Phys. 95 (2004) 6942–6944. [10] P. Mungsantisuk, R.P. Corson, S. Guruswamy, J. Appl. Phys. 98 (2005) 1–6, 123907.
[11] J.B. Restorff, M. Wun-Fogle, A.E. Clark, T.A. Lograsso, A.R. Ross, D.L. Schlagel, J. Appl. Phys. 91 (2002) 8225–8227. [12] C. Bormio-Nunes, R. Sato Turtelli, H. Mueller, R. Grössinger, H. Sassik, M.A. Tirelli, J. Magn. Magn. Mater. 290 (2005) 820–822. [13] S.M. Na, A.B. Flatau, J. Appl. Phys. 103 (2008) 1–3, 07D304. [14] A.E. Clark, J.B. Restorff, M. Wun-Fogle, K.B. Hathaway, T.A. Lograsso, M. Huang, E. Summers, J. Appl. Phys. 101 (2007) 1–3, 09C507. [15] J.H. Li, X.X. Gao, J. Zhu, X.Q. Bao, T. Xia, M.C. Zhang, Scr. Mater. 63 (2010) 246–249. [16] W. Wu, J.H. Liu, C.B. Jiang, H.B. Xu, Appl. Phys. Lett. 103 (2013) 1–3, 262403. [17] T.Y. Jin, W. Wu, C.B. Jiang, Scr. Mater. 74 (2014) 100–103. [18] Z.Q. Yao, X. Tian, L.P. Jiang, H.B. Hao, G.R. Zhang, S.X. Wu, Z.Q. Zhao, N. Gerile, J. Alloys Compd. 637 (2015) 431–435. [19] L.P. Jiang, J.D. Yang, H.B. Hao, G.R. Zhang, S.X. Wu, Y.J. Chen, O. Obi, T. Fitchorov, V.G. Harris, Appl. Phys. Lett. 102 (2013) 1–4, 222409. [20] T. Fitchorov, S. Bennett, L.P. Jiang, G.R. Zhang, Z.Q. Zhao, Y.J. Chen, V.G. Harris, Acta Mater. 73 (2014) 19–26. [21] W. Wu, J.H. Liu, C.B. Jiang, J. Alloys Compd. 622 (2015) 379–383.
Contents lists available at ScienceDirect
Scripta Materialia journal homepage: www.elsevier.com/locate/scriptamat
Regular Article
Magnetostriction of a Fe83Ga17 single crystal slightly doped with Tb Chongzheng Meng, Chengbao Jiang ⁎ Key Laboratory of Aerospace Materials and Performance, Ministry of Education, School of Materials Science and Engineering, Beihang University, Beijing 100191, PR China
a r t i c l e
i n f o
Article history: Received 12 October 2015 Received in revised form 17 November 2015 Accepted 19 November 2015 Available online xxxx Keywords: Magnetostriction FeGaTb single crystal Sub-rapid directional solidification
a b s t r a c t A novel strategy of sub-rapid directional solidification is developed for preparing doped FeGa single crystals. Crystals of nominal composition Fe83Ga17Tbx (x = 0, 0.05) have been grown with [100] preferred orientation at a high growth rate of 3000 mm/h. Using this method, trace amounts of normally-insoluble Tb can be incorporated into the A2 Fe83Ga17 matrix. A large magnetostriction (λ100) of 310 ppm is achieved in the [100] oriented Fe83Ga17Tb0.05 single crystal, ~50% higher than that of a similar undoped crystal. © 2015 Elsevier B.V. All rights reserved.
The past few decades have witnessed extensive applications of magnetostrictive materials in different fields such as sensors, actuators and transducers [1,2]. The giant room-temperature magnetostriction of Terfenol-D (Tb1 − xDyxFe2) alloys has been widely used in these fields. However, Terfenol-D is limited by its mechanical brittleness, heavy use of rare earth elements and high magnetic saturation field [3]. Galfenol (Fe1 − xGax) alloys have the advantages of excellent ductility, low cost and low magnetic saturation field [4]. Magnetostriction or iron is enhanced tenfold when a fraction of the iron atoms are replaced by nonmagnetic Ga [5–8], although it is still much lower than that of Terfenol-D. Great efforts have been made to further improve the magnetostriction by adding 3d and 4d transition elements such as Ni, V, Cr, Mn, Co, Mo, and Rh [9–12], or interstitial elements such as C, B and N [13–15]. Despite all that, there was no significant enhancement in the magnetostriction. However, it was recently reported that the magnetostriction of Fe83Ga17 alloys could be remarkably increased by melt spinning with small amount of rare earth elements such as Tb, Dy and Ce [16–18], although the perpendicularly grown grains in the meltspun ribbons make it very difficult to measure the magnetostriction directly. Moreover, due to the large demagnetizing field, the shape anisotropy of the ribbons also leads to a high magnetic saturation field. Enhanced magnetostriction with lower applied field is expected in bulk FeGa slightly doped with rare earth elements, but it is hard to obtain such materials by conventional methods. Very recently, bulk Fe83Ga17Tbx has been prepared by a directional casting process and magnetostriction of up to 160 ppm was obtained in polycrystalline Fe83Ga17Tb0.2 alloys [19,20]. However, the relatively slow cooling rate limits the solid solubility of Tb in the A2 matrix of
⁎ Corresponding author. E-mail address: [email protected] (C. Jiang).
http://dx.doi.org/10.1016/j.scriptamat.2015.11.022 1359-6462/© 2015 Elsevier B.V. All rights reserved.
the FeGa alloy, and a sound magnetostriction could not be obtained by this method. Therefore, a novel strategy combining rapid solidification with directional solidification, is urgently required to achieve magnetostriction in Tb-doped Fe83Ga17 crystals. In this report, we develop a sub-rapid directional solidification procedure. [100] oriented Fe 83 Ga 17 single crystals slightly doped with Tb have been prepared, and their magnetostriction (λ 100 ) of up to 310 ppm is approximately 50% higher than that of undoped Fe83Ga17 crystals, and almost twice as high as previously reported for Fe83Ga17Tb0.2 prepared by directional casting [19]. The nominal Fe83Ga17Tbx (x = 0, 0.05) master alloys were prepared by arc melting from high purity starting elements Fe, Ga and Tb (99.99%). Each ingot was re-melted four times under an argon atmosphere and cast in a chilled copper mold to obtain master rods. The crystals were grown in a sub-rapid directional solidification furnace. Master rods were first entirely melted and then moved downwards into cooling medium at velocities of 1000 mm/h, 3000 mm/h or 6000 mm/h. Afterwards, the directional microstructure and the magnetostriction of the polycrystalline specimens were measured. Following that, x = 0.05 Tb-doped Fe83Ga17 and x = 0 undoped Fe83Ga17 single crystals were grown at a velocity of 3000 mm/h based on a [100] oriented Fe83Ga17 seed crystal as shown in Fig. 1. The crystals were then cut into sheets 3 mm × 4 mm × 1.3 mm with six [100] faces. The crystallographic structure was identified by X-ray diffraction (XRD, D/MAX 2200 PC) with CuKα radiation (λ = 154.18 pm) and scanning speed of 6°/min. The microscopic morphology of the crystals was determined by using a JEOL JXA8100 electron probe micro-analyzer (EPMA). The preferred orientation of the single crystals was determined by the Lauë back-reflection X-ray technique. Magnetostriction was measured by the standard strain gauge method, and magnetization hysteresis loops (M–H) were measured with a Quantum Design physical property measurement system (PPMS-9).
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C. Meng, C. Jiang / Scripta Materialia 114 (2016) 9–12
Fig. 1. Schematic illustration of sub-rapid directional solidification equipment.
It has been found that rapid solidification (melt spinning) can be used to prepare rare-earth doped FeGa solid solutions, resulting in a significant increase of magnetostriction [16–18]. It has also been proved that the directional solidification method can enhance the magnetostriction of FeGa alloys by realizing [100] orientation which has the highest value of anisotropic magnetostriction [6]. In order to incorporate the advantages of both rapid solidification and directional solidification concurrently, an optimal cooling rate (R = GL × V) is required, where GL is the liquid temperature gradient in front of the solid–liquid interface and V is the growth velocity. This can be realized with a large GL and V. We develop a novel strategy to achieve sub-rapid solidification, as shown in Fig. 1. In this equipment, high-frequency induction
coils and graphite sleeves are employed to melt the master rods. The liquid metal cooling medium (Ga–In) combined with a floating ceramic baffle (BN) was adopted in order to achieve large GL; V can be manipulated over a range of 1000–10,000 mm/h. Fig. 2(a) shows the granular morphology of polycrystalline Fe 83 Ga 17 Tb 0.05 in longitudinal sections of specimens prepared at different velocities. Columnar grains can be clearly observed along the growth direction in the 1000 mm/h and 3000 mm/h specimens, while lateral grains are found in the 6000 mm/h specimen. It appears that a growth velocity less than 3000 mm/h is beneficial for directional solidification. Furthermore, back-scattered electron (BSE) imaging has been employed to analyze the phase composition in Fe83Ga17Tb0.05 specimens. In Fig. 2(b), there are obvious bright spheres and rods distributed in a dark background in the 1000 mm/h specimen, suggesting that a second phase precipitates from the matrix along grain boundaries. The 3000 mm/h and 6000 mm/h specimens observed are single phase. Energy-dispersive X-ray spectroscopy (EDS) analysis confirms that the precipitates in the 1000 mm/h specimen are Tb-rich, possessing the rhombohedral Th2Zn17 structure (2:17R), consistent with our previous work [21]. This indicates that the solid solution of a trace amount of Tb can be achieved at a growth velocity of 3000 mm/h or more. Fig. 2(c) shows the XRD patterns of Fe83Ga17Tb0.05 specimens prepared at 1000 mm/h, 3000 mm/h and 6000 mm/h. All diffraction peaks are indexed as (110), (200) and (211) on the body-centered cubic (bcc) structure, demonstrating that the matrix of all the Tb-doped Fe83Ga17 alloys possesses the same bcc structure as the binary Fe83Ga17 alloy. Meanwhile, the intensity of the (200) diffraction peak increases with growth velocities up to a maximum at 3000 mm/h, suggesting that this velocity is beneficial for [100] preferred oriented growth. The magnetostriction of a Fe83Ga17Tb0.05 specimen (Ф 7 mm × 20 mm) is summarized in Fig. 2(d). With the increase of growth velocity, the magnetostriction changes significantly, to a maximum of 200 ppm at a growth velocity of 3000 mm/h, which can be attributed to the [100] orientation and the solid solution of Tb. Therefore, rapid solidification and directional solidification are concurrently achieved at 3000 mm/h in a sub-rapid directional solidification process. The solid solution of Tb was suppressed below a velocity of 3000 mm/h, whereas directional growth was impeded above a velocity of 3000 mm/h. Thus, we
Fig. 2. Characterization of Fe83Ga17Tb0.05 crystals prepared at different growth velocities of 1000 mm/h, 3000 mm/h or 6000 mm/h: (a) optical metallographic graphs of Fe83Ga17Tb0.05 crystals; (b) BSE images of the Fe83Ga17Tb0.05 crystals; (c) XRD patterns of Fe83Ga17Tb0.05 crystals; (d) magnetostriction of Fe83Ga17Tb0.05 crystals.
C. Meng, C. Jiang / Scripta Materialia 114 (2016) 9–12
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Fig. 3. (a) XRD pattern of a Fe83Ga17Tb0.05 single crystal (Inset: Lauë spots of the single crystal); (b) magnetostriction of the Fe83Ga17Tb0.05 single crystal, where curve A is the measured value and curve B is the calculated value without demagnetizing field (Inset: the magnetization hysteresis loops in first quadrant).
successfully prepared Fe83Ga17Tb0.05 polycrystals, where [100] orientation and large magnetostriction are achieved, which provide a basis for then preparing large Tb doped Fe83Ga17 single crystals. For Fe83Ga17Tb0.05 single crystal preparation, we used a [100] oriented Fe83 Ga 17 single crystal as a seed, to grow a [100] oriented Fe 83Ga 17 Tb0.05 single crystal at 3000 mm/h. Fig. 3(a) shows the XRD pattern of the as-prepared Fe83Ga17Tb0.05 single crystal. There is only one sharp (200) bcc diffraction peak near 64°, indicating the single crystal nature of the FeGa alloy. The orientation is confirmed by X-ray Lauë back-reflection. From the inset in Fig. 3(a), clear and perfect Lauë spots, as well as four-fold symmetry can be observed, confirming that the single crystal is in the [100] orientation. Fig. 3(b) shows the measured magnetostriction of the Fe83Ga17Tb0.05 single crystal (curve A); a magnetostriction of 310 ppm is achieved along the [100] direction. The slight addition of Tb considerably enhances the magnetostriction of FeGa. It can be seen from the magnetization curve (Fig. 3(b) inset) that the saturation magnetization of the Fe 83 Ga 17 Tb 0.05 single crystal is approximately 18 kOe and the magnetic saturation field is near 2.7 kOe. The demagnetizing factor in the longitudinal dimension N is about 0.15. Curve B shows the calculated magnetostriction without the demagnetizing field, and the effective saturation field is calculated to be nearly 300 Oe, which is in accordance with a previous report in undoped Fe83Ga17 [6]. In order to investigate the solid solubility of Terbium, step-scanned XRD was used to measure the (200) diffraction peak patterns of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals at 2°/min, as shown in Fig. 4(a). The (200) diffraction peak of Fe83Ga17Tb0.05 shows a clear broadening and shift to lower angles compared to that of the Fe83Ga17 crystal.
The (200) diffraction peaks of the Fe83Ga17Tb0.05 and Fe83Ga17 crystals at 63.88° and 63.99° correspond to lattice constants a0 of 291.1 pm and 290.6 pm, respectively. It is reasonable to assume that lattice expansion causes the movement of the diffraction peak, implying that Tb dissolved in the matrix, as expected. Additionally, the (200) peak broadens, which can be attributed to microstrain in the matrix, also confirming the solid solution of Tb. The magnetostriction of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals is compared in Fig. 4(b); a λ100 of 195 ppm is measured in the Fe83Ga17 single crystal, similar to a previous report [6]. The magnetostriction of the Fe83Ga17Tb0.05 single crystal is nearly 1.5 times greater. We conclude that the solid solution of terbium increases the magnetostriction significantly. In conclusion, a sub-rapid directional solidification strategy has been developed to achieve rapid and directional solidification simultaneously. Fe83Ga17 single crystals with [100] orientation were prepared with trace amounts of dissolved terbium. The nominal Fe83Ga17Tb0.05 single crystal exhibits a magnetostriction (λ100) of 310 ppm, which is 50% higher than that of the undoped Fe83Ga17 single crystal. Our work illustrates a promising approach to preparing other advanced structural and functional materials which contains trace quantities of insoluble dopants. Acknowledgment The authors are grateful to Professor J. M. D. Coey for fruitful discussion and revision of manuscript. This work was supported by the National Natural Science Foundation of China (NSFC) under Grant No. 51331001, and the National Basic Research Program of China (973 Program) under Grant No. 2012CB619404.
Fig. 4. (a) Step-scanned XRD patterns of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals; (b) magnetostriction of Fe83Ga17Tb0.05 and Fe83Ga17 single crystals.
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C. Meng, C. Jiang / Scripta Materialia 114 (2016) 9–12
References [1] J. Atulasimha, A.B. Flatau, E. Summers, Smart Mater. Struct. 16 (2007) 1265–1276. [2] J.M.D. Coey, Magnetism and Magnetic Materials, Cambridge University Press, New York, 2010 1. [3] A.E. Clark, Ferromagnetic Materials Vol. 1, North-Holland, Amsterdam, 1980 531. [4] H. Wang, Y.N. Zhang, T. Yang, Z.D. Zhang, L.Z. Sun, R.Q. Wu, Appl. Phys. Lett. 97 (262505) (2010) 1–4. [5] E.M. Summers, T.A. Lograsso, M. Wun-Fogle, J. Mater. Sci. 42 (2007) 9582–9594. [6] H.D. Chopra, M. Wuttig, Nature 521 (2015) 340–351. [7] A.E. Clark, J.B. Restorff, M. Wun-Fogle, T.A. Lograsso, D.L. Schlagel, IEEE Trans. Magn. 36 (2000) 3238–3240. [8] J.B. Restorff, M. Wun-Fogle, K.B. Hathaway, A.E. Clark, T.A. Lograsso, G. Petculescu, J. Appl. Phys. 111 (2012) 1–12, 023905. [9] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, G. Petculescu, J. Appl. Phys. 95 (2004) 6942–6944. [10] P. Mungsantisuk, R.P. Corson, S. Guruswamy, J. Appl. Phys. 98 (2005) 1–6, 123907.
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