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Tb solid solution and enhanced magnetostriction in Fe83Ga17 alloys
Journal of Alloys and Compounds 622 (2015) 379–383
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Letter
Tb solid solution and enhanced magnetostriction in Fe83Ga17 alloys Wei Wu, Jinghua Liu ⇑, Chengbao Jiang Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 7 July 2014 Received in revised form 24 August 2014 Accepted 19 September 2014 Available online 5 October 2014 Keywords: Fe–Ga alloy Terbium Solid solution Magnetostriction
a b s t r a c t Three methods, casting, melt-quenching and melt-spinning were applied for preparing Tb-doped (Fe0.83Ga0.17)100xTbx (0 6 x 6 0.47). The magnetostriction improved drastically by Tb solid dissolved in Fe83Ga17 alloys. A giant perpendicular magnetostrictions k\ up to 886 ppm was achieved in the (Fe0.83Ga0.17)99.77Tb0.23 melt-spun ribbons. The enhanced magnetostriction was thought to be associated with the strong local magnetocrystalline anisotropy caused by the Tb doping into Fe83Ga17 alloys. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The substitution of nonmagnetic Ga in Fe enhances the magnetostriction k over tenfold, which has drawn lots of attentions [1–4]. With relatively high magnetostriction, low coercivity and good ductility, Fe–Ga alloy is a promising magnetostrictive material for magnetic actuators and sensors [5–12]. According to the previous studies of Fe100xGax alloys, local magnetocrystalline anisotropy induced by Ga–Ga pair defects is believed to responsible for the enhanced magnetostriction [13–14]. If the local magnetocrystalline anisotropy is further enhanced, the magnetostriction of Fe–Ga alloys would be improved. Tb element possesses a strong magnetic anisotropy originating from the strong coupling between the spin and the orbits of the 4f electrons. Hence, Tb doping into the Fe–Ga alloys is proposed and a giant magnetostriction is expected. Focusing on Tb-doped Fe–Ga alloys, Jiang et al. reported the increase of magnetostriction from 72 ppm to 160 ppm in the directionally solidified Fe83Ga17Tbx (x = 0.2) polycrystalline alloys [9]. The increase of the magnetostriction was attributed to the formation of preferential orientation enhanced by the precipitation of Tb-rich phase [9]. Further, in the [110]-textured Fe81Ga19Tbx (x = 0.3) polycrystalline alloy, Fitchorov et al. found that Tb doping resulted in an increase in magnetization, a reduction of saturation field and a decrease in magnitude of the temperature coefficient of the mangetostriction [12]. Recently, we have found that in case of
⇑ Corresponding author. Tel.: +86 10 82316234; fax: +86 10 82338200. E-mail address: [email protected] (J. Liu). http://dx.doi.org/10.1016/j.jallcom.2014.09.151 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
rapid solidification the solid solution of Tb element in the A2 matrix of Fe83Ga17 ribbons induced the fivefold giant magnetostriction compared with that of the binary Fe83Ga17 ribbon [8]. It was indicated that Tb solid solubility in Fe–Ga–Tb alloys might be a main contributor for further magnetostriction enhancement. To confirm this suggestion, this paper work focuses on the Tb solid solubility in Fe83Ga17 alloy under a wide range of cooling rates, the corresponding structural changes and magnetostrictive enhancement. We prepared terbium-doped (Fe0.83Ga0.17)100xTbx (0 6 x 6 0.47) alloys by casting, melt-quenching and melt-spinning respectively, with different cooling rates. The results indicated that the Tb-rich precipitation obviously appeared for casting while little for melt-quenching, and Tb solid dissolved up to x = 0.23 in the A2 matrix for melt-spinning. The magnetostriction improved drastically with increasing the cooling rate. The enhanced magnetostriction was associated with the Tb solid solution in the A2 matrix. 2. Experimental Precursor ingots of (Fe0.83Ga0.17)100xTbx (x = 0–0.47) were prepared from iron, gallium and terbium with a purity of 99.99% by arc-melting under argon atmosphere four times. The weight loss of the ingots was precisely controlled to be less than 1%. The ingots drop casted in chilled copper mold by arc melting to obtain ascast rods with the diameter of 7.2 mm. The melt-quenched samples were melted by induction melting and quenched into the liquid Ga–In alloy. Melt-spinning ribbons were prepared with the copper wheel velocity of 20 m/s. All of the three preparation processes were shown in the Fig. 1. The cooling rates were evaluated to be 101 K/s for casting, 102 K/s for melt-quenching and 106 K/s for melt-spinning [15], respectively. The crystal structure was characterized by X-ray diffraction (XRD) on a Rigaku X-ray diffractometer with Cu Ka radiation. The composition and morphology were determined using a JEOL JXA-8100 electron probe micro-analyzer (EPMA) and a JEOL JEM-2100 transmission electron microscope (TEM). The
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Fig. 1. Schematic diagram of (a) casting, (b) melt-quenching and (c) melt-spinning preparation methods.
magnetostrictions were tested along the axial direction for the as-cast and meltquenched rods and along the length direction for the ribbons by the standard resistance strain gauge technique [17–18]. The magnetostriction was measured three times for each sample with strain gauges stuck on both sides of the ribbon.
3. Results and discussions Fig. 2 shows the back scattered electron (BSE) graphs of the ascast, melt-quenched alloys and melt-spun ribbons. Dual-phase microstructure is observed for the as-cast (Fe0.83Ga0.17)100xTbx (x = 0.06–0.47) samples, as shown in Fig. 2(a)–(c), where the
second phase (the white area) distributes along grain boundaries. The volume fraction of the second phase in the melt-quenched alloys is much less, compared with the as-cast alloys, as shown in the Fig. 2(d)–(f). The energy dispersive spectroscopy (EDS) tests confirm that the compositions of the secondary phases in the as-cast and melt-quenched samples are similar, with 60 at% Fe, 30 at% Ga and 10 at% Tb. The microstructures of the melt-spun ribbons are quite different. As Fig. 2(g)–(i), no secondary phases are monitored by BSE in the ribbons up to x = 0.23. Only a small quantity of nano-sized globular Tb-rich precipitates are observed in the x = 0.47 ribbon by TEM, shown in Fig. 2(h) and (i) inserts.
Fig. 2. The back scattered electron (BSE) graphs of the (Fe0.83Ga0.17)100xTbx (x = 0.06, 0.23, 0.47) alloys prepared by using (a–c) casting, (d–f) melt-quenching and (g–i) meltspinning methods respectively. Insets are TEM bright-field images of (Fe0.83Ga0.17)100xTbx ribbons (x = 0.23, 0.47).
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(a)
(b)
* 2:17R Intensity (a.u.)
CastedTb0.47
*
*
**
*
**
Melt-quenched Tb0.47
30
40
50
60
70
80
2theta (deg.) Fig. 3. (a) XRD patterns of casted, melt-quenched and melt-spun x = 0.47 samples. (b) The amplifying XRD patterns of casted, melt-quenched x = 0.47 samples show the additional peaks belong to the 2:17 type Tb-rich precipitation phase.
The precipitation of Tb-rich phase in the as-cast samples, especially in the (Fe0.83Ga0.17)99.94Tb0.06 alloy, indicates that a quite low solubility of Tb in Fe83Ga17 alloy under a low cooling rate. The rapid solidification gives rise to solute little Tb element for melt-quenching, which is evidenced by the precipitation totally eliminated at x = 0.06. Much more Tb element is solid-dissolved in the Fe83Ga17 melt-spun ribbons under high cooling rate. A single phase is observed for the ribbons by high resolution TEM with Tb content up to x = 0.23. The results indicate Tb solid solution increases with increasing the cooling rate. The solid solubility limit of Tb in Fe83Ga17 alloy is less than x = 0.06 for casting, more than x = 0.06 for melt quenching and up to x = 0.23 for melt spinning, respectively. The crystal structure of the samples is checked by X-ray diffractions, as shown in Fig. 3. Four main diffraction peaks are observed for all the alloys, which are indexed as (1 1 0), (2 0 0), (2 1 1) and (2 2 0) from the body-centered cubic (bcc) structure. This demonstrates that the matrix of all the Tb-doped Fe83Ga17 alloys possesses the same bcc structure as that of the binary Fe83Ga17 alloy. The additional peaks, as shown in Fig. 3(b), are presented in the XRD patterns for the as-cast and melt-quenched alloys with x = 0.47, which should be attributed to the Tb-rich precipitation.
According to the Fe–Tb binary phase diagram [16] and combining with the EDS results, it is suggested that the crystal structure of the secondary phase is the rhombohedra Th2Zn17 structure (2:17R), as shown in Fig. 3(b). The peak intensities of the Tb-rich precipitation for the melt-quenched Tb-doped alloys are weaker than those for as-cast alloys. The results approve that the volume fractions of the second phase for melt-quenched alloys are less than that for as-cast samples, agreeing with the microstructure observed in Fig. 1(a)–(f). The small quantity of the precipitated phase cannot be detected by X-ray diffraction for x = 0.47 melt-spun ribbons, as shown in Fig. 3(b). The above results further prove that the solid solubility of the large Tb atoms in A2 matrix increases with increasing the cooling rate. The lattice parameters a0 of A2 phase matrix for all alloys are calculated, as plotted in Fig. 4(a). With increasing Tb addition, the lattice parameters for casted alloys increases first from a0 = 2.8996 Å for Fe83Ga17 to a0 = 2.9022 Å for x = 0.06 and then decrease to a0 = 2.8991 Å for x = 0.47. The lattice parameters for the melt-quenched alloys increase first from a0 = 2.8997 Å for Fe83Ga17 to a maximum of a0 = 2.9034 Å for x = 0.12 and then decreasing to a0 = 2.8999 Å for x = 0.47. For the ribbons, the lattice
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2.907
(a)
Casted samples
2.906
Melt-quenched samples
2.905
Melt-spun samples
a (Å)
2.904 2.903 2.902 2.901 2.900 2.899 2.898
0.0
0.1
0.2
0.3
0.4
0.5
Perpendicularmagnetostrictions for the ribbons (ppm)
(b)
-1000
160
Melt-spun samples
-900
Casted samples
-800
140
Melt-quenched samples
-700
120
-600
100
-500
80
-400 60
-300
40
-200 -100 0.0
0.1
0.2
0.3
0.4
20 0.5
Parallel magnetostrictions for the casted and melt-quenched samples (ppm)
Tb content (at%)
Tb content (at%) Fig. 4. Tb addition dependence of the (a) lattice constant and (b) magnetostriction of (Fe0.83Ga0.17)100xTbx alloys by casting, melt-quenching and melt-spinning methods.
parameters monotonously increase up to x = 0.23, and almost keep constant at x = 0.47. The initial increase of the lattice parameter is associated with the doping of the large Tb atoms into the A2 matrix. And the decrease for higher Tb addition is attributed to the precipitation of the Tb-rich phase. The magnetostrictions have been measured totally six times for each sample, as mentioned above. The average values of the magnetostrictions under 1 T applied field are plotted in Fig. 4(b). For ascast alloys, parallel magnetostrictions kk are increased from 28 ppm for Fe83Ga17 (x = 0) to 56 ppm for x = 0.06 first and then decrease to 30 ppm for x = 0.47. Similar enhanced magnetostriction was reported in Fe83Ga16.8Tb0.2 directional casted alloy [9]. For melt-quenched alloy, the average magnetostriction equals to 30 ppm for the binary Fe83Ga17 (x = 0), close to that of the as-cast alloy, and improves to 85 ppm for x = 0.12, and then gradually decreases to 25 ppm for x = 0.47. The maximum magnetostriction for x = 0.12 alloy is 2.8 times as large as that for binary Fe83Ga17 melt-quenched alloy. The perpendicular magnetostrictions k\ for the (Fe0.83Ga0.17)100x Tbx melt-spun ribbons are measured along the length of the ribbon samples with the applied field normal to the ribbons. The crystal growth is normal to the plane of ribbons with < 001 > preferred orientation and the magnetic field is also along the axis of the columnar grains in fact. Since the thickness of the ribbons is very thin of about 20 lm, the parallel magnetostrictions kk is difficult to be tested. The calculated kk = 2k\ here [19]. The average magnetostriction k\ for the binary Fe83Ga17 (x = 0) ribbon is
176 ppm, consistent with the previously reported value of 163 ppm for Fe81Ga19 ribbon [20]. Surprisingly, the magnetostriction for the (Fe0.83Ga0.17)100xTbx melt-spun ribbons is improved greatly by doped a small amount of Tb. The average magnetostriction k\ dramatically increase up to 447 ppm for x = 0.06, 886 ppm for x = 0.23 and then slightly decease to 862 ppm for x = 0.47. For melt-spun samples, the enhanced magnetostriction with Tb doping for x = 0.23 ribbon is four times larger than that for binary Fe83Ga17 ribbon. It is noteworthy that the increase tendency of the magnetostrictions for all samples with increasing Tb addition is very similar with that of the lattice parameters. As seen in the Fig. 4(a) and (b), the maximum of magnetostriction locates at the Tb solid solubility limit in A2 matrix for all of the samples. This results show that the enhancement of the lattice parameter and the improvement of magnetostriction are correlated, attributing from the solid solution of Tb in the A2 matrix. Comparing three methods with different cooling rate, it can be concluded that the faster cooling rate causes the higher solid solubility of Tb in Fe–Ga alloy, leading to larger enhancement in magnetostrictions. The magnetostriction and the magnetocrystalline anisotropy of Fe–Ga alloys both originate from the spin–orbit coupling [13, 21]. As supposed that the local magnetocrystalline anisotropy from Ga–Ga pair defects enhances the magnetostriction tenfold with the substitution of nonmagnetic Ga in Fe, the achieved large magnetostriction is induced by further enhancing the local magnetocrystalline anisotropy with trace Tb doping in Fe83Ga17 alloy.
W. Wu et al. / Journal of Alloys and Compounds 622 (2015) 379–383
4. Conclusion In summary, (Fe0.83Ga0.17)100xTbx (x = 0–0.47) alloys are prepared under different cooling rates by applying the as-cast, meltquenched and melt-spun methods, respectively. The solid solubility of Tb atoms in A2 matrix increases with increasing the cooling rate. The magnetostriction is improved drastically by Tb solid dissolved in Fe83Ga17 alloys. The enhanced magnetostriction is associated with the strong local magnetocrystalline anisotropy caused by the Tb doping. Acknowledgements This work is supported by National Basic Research Program (2012CB619404), Natural Science Foundation of China (51331001, 51221163, 51101006 and 91016006). References [1] D.C. Jiles, Acta Mater. 51 (2003) 5907. [2] J.X. Zhang, L.Q. Chen, Acta Mater. 53 (2005) 2845. [3] H. Basumatary, M. Palit, J.A. Chelvane, S. Pandian, Chandrasekaran, Scr. Mater. 59 (2008) 878.
M.M.
Raja,
V.
383
[4] T.A. Lograsso, A.R. Ross, D.L. Schlagel, A.E. Clark, M. Wun-Fogle, J. Alloys Comp. 350 (2003) 95. [5] J.H. Liu, F. Yi, C.B. Jiang, J. Alloys Comp. 481 (2009) 57. [6] H. Wang, Y.N. Zhang, T. Yang, Z.D. Zhang, L.Z. Sun, R.Q. Wu, Appl. Phys. Lett. 97 (2010) 262505. [7] A. Mahadevan, P.G. Evans, M.J. Dapino, Appl. Phys. Lett. 96 (2010) 012502. [8] W. Wu, J.H. Liu, C.B. Jiang, H.B. Xu, Appl. Phys. Lett. 103 (2013) 262403. [9] L.P. Jiang, J.D. Yang, H.B. Hao, G.R. Zhang, S.X. Wu, Y.J. Chen, O. Obi, T.I. Fitchorov, V.G. Harris, Appl. Phys. Lett. 102 (2013) 222409. [10] J.H. Liu, Z.B. Wang, C.B. Jiang, H.B. Xu, J. Appl. Phys. 108 (2010) 033913. [11] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, G. Petculescu, J. Appl. Phys. 95 (2004) 6942. [12] T.I. Fitchorov, S. Bennett, L.P. Jiang, G.R. Zhang, Z.Q. Zhao, Y.J. Chen, V.G. Harris, Acta Mater. 73 (2014) 19. [13] J. Cullen, P. Zhao, M. Wuttig, J. Appl. Phys. 101 (2007) 123922. [14] M.P. Ruffoni, S. Pascarelli, R. Grössinger, R. Sato Turtelli, C. Bormio-Nunes, R.F. Pettifer, Phys. Rev. Lett. 101 (2008) 147202. [15] X.X. Dong, L.J. He, P.J. Li, J. Alloys Comp. 612 (2014) 20–25. [16] K.H.J. Buschow, Ferromagnetic Materials, North-Holland, Amsterdam, 1980, p. 297. [17] T. Takahashi, K. Hashimoto, T. Okazaki, Y. Furuya, T. Kubota, C. Saito, Scr. Mater. 60 (2009) 847. [18] T.Y. Jin, W. Wu, C.B. Jiang, Scr. Mater. 74 (2014) 100. [19] J.M.D. Coey, Magnetism and Magnetic Materials, Cambridge University Press, New York, 2010, p. 176. [20] N. Mehmood, G. Vlasák, F. Kubel, R. Sato Turtelli, R. Grössinger, M. Kriegisch, H. Sassik, P. Svec, IEEE Trans. Magn. 45 (2009) 4128–4131. [21] A.E. Clark, Ferromagnetic Materials, North-Holland, Amsterdam, 1980, p. 531.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Letter
Tb solid solution and enhanced magnetostriction in Fe83Ga17 alloys Wei Wu, Jinghua Liu ⇑, Chengbao Jiang Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, People’s Republic of China
a r t i c l e
i n f o
Article history: Received 7 July 2014 Received in revised form 24 August 2014 Accepted 19 September 2014 Available online 5 October 2014 Keywords: Fe–Ga alloy Terbium Solid solution Magnetostriction
a b s t r a c t Three methods, casting, melt-quenching and melt-spinning were applied for preparing Tb-doped (Fe0.83Ga0.17)100xTbx (0 6 x 6 0.47). The magnetostriction improved drastically by Tb solid dissolved in Fe83Ga17 alloys. A giant perpendicular magnetostrictions k\ up to 886 ppm was achieved in the (Fe0.83Ga0.17)99.77Tb0.23 melt-spun ribbons. The enhanced magnetostriction was thought to be associated with the strong local magnetocrystalline anisotropy caused by the Tb doping into Fe83Ga17 alloys. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction The substitution of nonmagnetic Ga in Fe enhances the magnetostriction k over tenfold, which has drawn lots of attentions [1–4]. With relatively high magnetostriction, low coercivity and good ductility, Fe–Ga alloy is a promising magnetostrictive material for magnetic actuators and sensors [5–12]. According to the previous studies of Fe100xGax alloys, local magnetocrystalline anisotropy induced by Ga–Ga pair defects is believed to responsible for the enhanced magnetostriction [13–14]. If the local magnetocrystalline anisotropy is further enhanced, the magnetostriction of Fe–Ga alloys would be improved. Tb element possesses a strong magnetic anisotropy originating from the strong coupling between the spin and the orbits of the 4f electrons. Hence, Tb doping into the Fe–Ga alloys is proposed and a giant magnetostriction is expected. Focusing on Tb-doped Fe–Ga alloys, Jiang et al. reported the increase of magnetostriction from 72 ppm to 160 ppm in the directionally solidified Fe83Ga17Tbx (x = 0.2) polycrystalline alloys [9]. The increase of the magnetostriction was attributed to the formation of preferential orientation enhanced by the precipitation of Tb-rich phase [9]. Further, in the [110]-textured Fe81Ga19Tbx (x = 0.3) polycrystalline alloy, Fitchorov et al. found that Tb doping resulted in an increase in magnetization, a reduction of saturation field and a decrease in magnitude of the temperature coefficient of the mangetostriction [12]. Recently, we have found that in case of
⇑ Corresponding author. Tel.: +86 10 82316234; fax: +86 10 82338200. E-mail address: [email protected] (J. Liu). http://dx.doi.org/10.1016/j.jallcom.2014.09.151 0925-8388/Ó 2014 Elsevier B.V. All rights reserved.
rapid solidification the solid solution of Tb element in the A2 matrix of Fe83Ga17 ribbons induced the fivefold giant magnetostriction compared with that of the binary Fe83Ga17 ribbon [8]. It was indicated that Tb solid solubility in Fe–Ga–Tb alloys might be a main contributor for further magnetostriction enhancement. To confirm this suggestion, this paper work focuses on the Tb solid solubility in Fe83Ga17 alloy under a wide range of cooling rates, the corresponding structural changes and magnetostrictive enhancement. We prepared terbium-doped (Fe0.83Ga0.17)100xTbx (0 6 x 6 0.47) alloys by casting, melt-quenching and melt-spinning respectively, with different cooling rates. The results indicated that the Tb-rich precipitation obviously appeared for casting while little for melt-quenching, and Tb solid dissolved up to x = 0.23 in the A2 matrix for melt-spinning. The magnetostriction improved drastically with increasing the cooling rate. The enhanced magnetostriction was associated with the Tb solid solution in the A2 matrix. 2. Experimental Precursor ingots of (Fe0.83Ga0.17)100xTbx (x = 0–0.47) were prepared from iron, gallium and terbium with a purity of 99.99% by arc-melting under argon atmosphere four times. The weight loss of the ingots was precisely controlled to be less than 1%. The ingots drop casted in chilled copper mold by arc melting to obtain ascast rods with the diameter of 7.2 mm. The melt-quenched samples were melted by induction melting and quenched into the liquid Ga–In alloy. Melt-spinning ribbons were prepared with the copper wheel velocity of 20 m/s. All of the three preparation processes were shown in the Fig. 1. The cooling rates were evaluated to be 101 K/s for casting, 102 K/s for melt-quenching and 106 K/s for melt-spinning [15], respectively. The crystal structure was characterized by X-ray diffraction (XRD) on a Rigaku X-ray diffractometer with Cu Ka radiation. The composition and morphology were determined using a JEOL JXA-8100 electron probe micro-analyzer (EPMA) and a JEOL JEM-2100 transmission electron microscope (TEM). The
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Fig. 1. Schematic diagram of (a) casting, (b) melt-quenching and (c) melt-spinning preparation methods.
magnetostrictions were tested along the axial direction for the as-cast and meltquenched rods and along the length direction for the ribbons by the standard resistance strain gauge technique [17–18]. The magnetostriction was measured three times for each sample with strain gauges stuck on both sides of the ribbon.
3. Results and discussions Fig. 2 shows the back scattered electron (BSE) graphs of the ascast, melt-quenched alloys and melt-spun ribbons. Dual-phase microstructure is observed for the as-cast (Fe0.83Ga0.17)100xTbx (x = 0.06–0.47) samples, as shown in Fig. 2(a)–(c), where the
second phase (the white area) distributes along grain boundaries. The volume fraction of the second phase in the melt-quenched alloys is much less, compared with the as-cast alloys, as shown in the Fig. 2(d)–(f). The energy dispersive spectroscopy (EDS) tests confirm that the compositions of the secondary phases in the as-cast and melt-quenched samples are similar, with 60 at% Fe, 30 at% Ga and 10 at% Tb. The microstructures of the melt-spun ribbons are quite different. As Fig. 2(g)–(i), no secondary phases are monitored by BSE in the ribbons up to x = 0.23. Only a small quantity of nano-sized globular Tb-rich precipitates are observed in the x = 0.47 ribbon by TEM, shown in Fig. 2(h) and (i) inserts.
Fig. 2. The back scattered electron (BSE) graphs of the (Fe0.83Ga0.17)100xTbx (x = 0.06, 0.23, 0.47) alloys prepared by using (a–c) casting, (d–f) melt-quenching and (g–i) meltspinning methods respectively. Insets are TEM bright-field images of (Fe0.83Ga0.17)100xTbx ribbons (x = 0.23, 0.47).
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(a)
(b)
* 2:17R Intensity (a.u.)
CastedTb0.47
*
*
**
*
**
Melt-quenched Tb0.47
30
40
50
60
70
80
2theta (deg.) Fig. 3. (a) XRD patterns of casted, melt-quenched and melt-spun x = 0.47 samples. (b) The amplifying XRD patterns of casted, melt-quenched x = 0.47 samples show the additional peaks belong to the 2:17 type Tb-rich precipitation phase.
The precipitation of Tb-rich phase in the as-cast samples, especially in the (Fe0.83Ga0.17)99.94Tb0.06 alloy, indicates that a quite low solubility of Tb in Fe83Ga17 alloy under a low cooling rate. The rapid solidification gives rise to solute little Tb element for melt-quenching, which is evidenced by the precipitation totally eliminated at x = 0.06. Much more Tb element is solid-dissolved in the Fe83Ga17 melt-spun ribbons under high cooling rate. A single phase is observed for the ribbons by high resolution TEM with Tb content up to x = 0.23. The results indicate Tb solid solution increases with increasing the cooling rate. The solid solubility limit of Tb in Fe83Ga17 alloy is less than x = 0.06 for casting, more than x = 0.06 for melt quenching and up to x = 0.23 for melt spinning, respectively. The crystal structure of the samples is checked by X-ray diffractions, as shown in Fig. 3. Four main diffraction peaks are observed for all the alloys, which are indexed as (1 1 0), (2 0 0), (2 1 1) and (2 2 0) from the body-centered cubic (bcc) structure. This demonstrates that the matrix of all the Tb-doped Fe83Ga17 alloys possesses the same bcc structure as that of the binary Fe83Ga17 alloy. The additional peaks, as shown in Fig. 3(b), are presented in the XRD patterns for the as-cast and melt-quenched alloys with x = 0.47, which should be attributed to the Tb-rich precipitation.
According to the Fe–Tb binary phase diagram [16] and combining with the EDS results, it is suggested that the crystal structure of the secondary phase is the rhombohedra Th2Zn17 structure (2:17R), as shown in Fig. 3(b). The peak intensities of the Tb-rich precipitation for the melt-quenched Tb-doped alloys are weaker than those for as-cast alloys. The results approve that the volume fractions of the second phase for melt-quenched alloys are less than that for as-cast samples, agreeing with the microstructure observed in Fig. 1(a)–(f). The small quantity of the precipitated phase cannot be detected by X-ray diffraction for x = 0.47 melt-spun ribbons, as shown in Fig. 3(b). The above results further prove that the solid solubility of the large Tb atoms in A2 matrix increases with increasing the cooling rate. The lattice parameters a0 of A2 phase matrix for all alloys are calculated, as plotted in Fig. 4(a). With increasing Tb addition, the lattice parameters for casted alloys increases first from a0 = 2.8996 Å for Fe83Ga17 to a0 = 2.9022 Å for x = 0.06 and then decrease to a0 = 2.8991 Å for x = 0.47. The lattice parameters for the melt-quenched alloys increase first from a0 = 2.8997 Å for Fe83Ga17 to a maximum of a0 = 2.9034 Å for x = 0.12 and then decreasing to a0 = 2.8999 Å for x = 0.47. For the ribbons, the lattice
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2.907
(a)
Casted samples
2.906
Melt-quenched samples
2.905
Melt-spun samples
a (Å)
2.904 2.903 2.902 2.901 2.900 2.899 2.898
0.0
0.1
0.2
0.3
0.4
0.5
Perpendicularmagnetostrictions for the ribbons (ppm)
(b)
-1000
160
Melt-spun samples
-900
Casted samples
-800
140
Melt-quenched samples
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120
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100
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80
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-200 -100 0.0
0.1
0.2
0.3
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Parallel magnetostrictions for the casted and melt-quenched samples (ppm)
Tb content (at%)
Tb content (at%) Fig. 4. Tb addition dependence of the (a) lattice constant and (b) magnetostriction of (Fe0.83Ga0.17)100xTbx alloys by casting, melt-quenching and melt-spinning methods.
parameters monotonously increase up to x = 0.23, and almost keep constant at x = 0.47. The initial increase of the lattice parameter is associated with the doping of the large Tb atoms into the A2 matrix. And the decrease for higher Tb addition is attributed to the precipitation of the Tb-rich phase. The magnetostrictions have been measured totally six times for each sample, as mentioned above. The average values of the magnetostrictions under 1 T applied field are plotted in Fig. 4(b). For ascast alloys, parallel magnetostrictions kk are increased from 28 ppm for Fe83Ga17 (x = 0) to 56 ppm for x = 0.06 first and then decrease to 30 ppm for x = 0.47. Similar enhanced magnetostriction was reported in Fe83Ga16.8Tb0.2 directional casted alloy [9]. For melt-quenched alloy, the average magnetostriction equals to 30 ppm for the binary Fe83Ga17 (x = 0), close to that of the as-cast alloy, and improves to 85 ppm for x = 0.12, and then gradually decreases to 25 ppm for x = 0.47. The maximum magnetostriction for x = 0.12 alloy is 2.8 times as large as that for binary Fe83Ga17 melt-quenched alloy. The perpendicular magnetostrictions k\ for the (Fe0.83Ga0.17)100x Tbx melt-spun ribbons are measured along the length of the ribbon samples with the applied field normal to the ribbons. The crystal growth is normal to the plane of ribbons with < 001 > preferred orientation and the magnetic field is also along the axis of the columnar grains in fact. Since the thickness of the ribbons is very thin of about 20 lm, the parallel magnetostrictions kk is difficult to be tested. The calculated kk = 2k\ here [19]. The average magnetostriction k\ for the binary Fe83Ga17 (x = 0) ribbon is
176 ppm, consistent with the previously reported value of 163 ppm for Fe81Ga19 ribbon [20]. Surprisingly, the magnetostriction for the (Fe0.83Ga0.17)100xTbx melt-spun ribbons is improved greatly by doped a small amount of Tb. The average magnetostriction k\ dramatically increase up to 447 ppm for x = 0.06, 886 ppm for x = 0.23 and then slightly decease to 862 ppm for x = 0.47. For melt-spun samples, the enhanced magnetostriction with Tb doping for x = 0.23 ribbon is four times larger than that for binary Fe83Ga17 ribbon. It is noteworthy that the increase tendency of the magnetostrictions for all samples with increasing Tb addition is very similar with that of the lattice parameters. As seen in the Fig. 4(a) and (b), the maximum of magnetostriction locates at the Tb solid solubility limit in A2 matrix for all of the samples. This results show that the enhancement of the lattice parameter and the improvement of magnetostriction are correlated, attributing from the solid solution of Tb in the A2 matrix. Comparing three methods with different cooling rate, it can be concluded that the faster cooling rate causes the higher solid solubility of Tb in Fe–Ga alloy, leading to larger enhancement in magnetostrictions. The magnetostriction and the magnetocrystalline anisotropy of Fe–Ga alloys both originate from the spin–orbit coupling [13, 21]. As supposed that the local magnetocrystalline anisotropy from Ga–Ga pair defects enhances the magnetostriction tenfold with the substitution of nonmagnetic Ga in Fe, the achieved large magnetostriction is induced by further enhancing the local magnetocrystalline anisotropy with trace Tb doping in Fe83Ga17 alloy.
W. Wu et al. / Journal of Alloys and Compounds 622 (2015) 379–383
4. Conclusion In summary, (Fe0.83Ga0.17)100xTbx (x = 0–0.47) alloys are prepared under different cooling rates by applying the as-cast, meltquenched and melt-spun methods, respectively. The solid solubility of Tb atoms in A2 matrix increases with increasing the cooling rate. The magnetostriction is improved drastically by Tb solid dissolved in Fe83Ga17 alloys. The enhanced magnetostriction is associated with the strong local magnetocrystalline anisotropy caused by the Tb doping. Acknowledgements This work is supported by National Basic Research Program (2012CB619404), Natural Science Foundation of China (51331001, 51221163, 51101006 and 91016006). References [1] D.C. Jiles, Acta Mater. 51 (2003) 5907. [2] J.X. Zhang, L.Q. Chen, Acta Mater. 53 (2005) 2845. [3] H. Basumatary, M. Palit, J.A. Chelvane, S. Pandian, Chandrasekaran, Scr. Mater. 59 (2008) 878.
M.M.
Raja,
V.
383
[4] T.A. Lograsso, A.R. Ross, D.L. Schlagel, A.E. Clark, M. Wun-Fogle, J. Alloys Comp. 350 (2003) 95. [5] J.H. Liu, F. Yi, C.B. Jiang, J. Alloys Comp. 481 (2009) 57. [6] H. Wang, Y.N. Zhang, T. Yang, Z.D. Zhang, L.Z. Sun, R.Q. Wu, Appl. Phys. Lett. 97 (2010) 262505. [7] A. Mahadevan, P.G. Evans, M.J. Dapino, Appl. Phys. Lett. 96 (2010) 012502. [8] W. Wu, J.H. Liu, C.B. Jiang, H.B. Xu, Appl. Phys. Lett. 103 (2013) 262403. [9] L.P. Jiang, J.D. Yang, H.B. Hao, G.R. Zhang, S.X. Wu, Y.J. Chen, O. Obi, T.I. Fitchorov, V.G. Harris, Appl. Phys. Lett. 102 (2013) 222409. [10] J.H. Liu, Z.B. Wang, C.B. Jiang, H.B. Xu, J. Appl. Phys. 108 (2010) 033913. [11] A.E. Clark, M. Wun-Fogle, J.B. Restorff, T.A. Lograsso, G. Petculescu, J. Appl. Phys. 95 (2004) 6942. [12] T.I. Fitchorov, S. Bennett, L.P. Jiang, G.R. Zhang, Z.Q. Zhao, Y.J. Chen, V.G. Harris, Acta Mater. 73 (2014) 19. [13] J. Cullen, P. Zhao, M. Wuttig, J. Appl. Phys. 101 (2007) 123922. [14] M.P. Ruffoni, S. Pascarelli, R. Grössinger, R. Sato Turtelli, C. Bormio-Nunes, R.F. Pettifer, Phys. Rev. Lett. 101 (2008) 147202. [15] X.X. Dong, L.J. He, P.J. Li, J. Alloys Comp. 612 (2014) 20–25. [16] K.H.J. Buschow, Ferromagnetic Materials, North-Holland, Amsterdam, 1980, p. 297. [17] T. Takahashi, K. Hashimoto, T. Okazaki, Y. Furuya, T. Kubota, C. Saito, Scr. Mater. 60 (2009) 847. [18] T.Y. Jin, W. Wu, C.B. Jiang, Scr. Mater. 74 (2014) 100. [19] J.M.D. Coey, Magnetism and Magnetic Materials, Cambridge University Press, New York, 2010, p. 176. [20] N. Mehmood, G. Vlasák, F. Kubel, R. Sato Turtelli, R. Grössinger, M. Kriegisch, H. Sassik, P. Svec, IEEE Trans. Magn. 45 (2009) 4128–4131. [21] A.E. Clark, Ferromagnetic Materials, North-Holland, Amsterdam, 1980, p. 531.