Journal of Alloys and Compounds 582 (2014) 583–587

Contents lists available at ScienceDirect

Journal of Alloys and Compounds

journal homepage: www.elsevier .com/locate / ja lcom

Magnetostriction of TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 compounds and theircomposites (0.20 6 x 6 0.60)

0925-8388/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.jallcom.2013.08.092

⇑ Corresponding author. Tel.: +86 13858375681.E-mail addresses: liujinjun1@nbu.edu.cn, liujjimr@gmail.com (J.J. Liu).

H.Y. Yin a, J.J. Liu a,⇑, Z.B. Pan a, X.Y. Liu a, X.C. Liu a, L.D. Liu b, J. Du b, P.Z. Si c

a Faculty of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, Chinab Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, Chinac College of Materials Science and Engineering, China Jiliang University, Hangzhou 310018, China

a r t i c l e i n f o

Article history:Received 27 March 2013Received in revised form 10 August 2013Accepted 13 August 2013Available online 23 August 2013

Keywords:MagnetostrictionMagnetocrystalline anisotropyLaves phaseMagnetostrictive composites

a b s t r a c t

The structure, spin configuration, magnetocrystalline anisotropy compensation, magnetic properties, andmagnetostriction of TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 (0.20 6 x 6 0.60) alloys are investigated. The easy mag-netization direction (EMD) at room temperature rotates from the h100i axis (x 6 0.25) to the h111i axis(x P 0.30) with increasing Tb content, subjected to the anisotropy compensation between Tb3+ and Dy3+

ions. The analysis of X-ray diffraction, EMD and magnetostriction show that TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93

is an anisotropy compensation system and the compensation point is realized around x = 0.30. The Lavesphase compound Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 has a large spontaneous magnetostriction, the coefficientk111 up to about 1640 ppm. The epoxy bonded 0–3 and pseudo-1–3 composites were fabricated by curingwithout and with a magnetic field. A high magnetostriction, longitudinal k|| and linear anisotropic ka(=k||�k\) up to around 390 and 650 ppm at 6 kOe, respectively, is obtained for the grain h111i-orientedpseudo-1–3 epoxy/Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 composite with 20 vol% alloy particles.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction

It has been well known that the cubic Laves phase compoundsRFe2 (R = rare earth) exhibit very large anisotropic magnetostrictionat room temperature, and the most famous one, Tb0.27Dy0.73Fe2

(Terfenol-D), has been widely used as actuators and transducers[1]. However, the heavy rare earths Tb and Dy are expensive, thusthe low-cost materials Pr and Nd have received more attentionsfor the view point of applications. According to the single-ion model[2], NdFe2 has a large theoretical magnetostriction (about2000 ppm at 0 K). Besides, the magnetocrystalline anisotropy con-stant K1 of both NdFe2 and DyFe2 are positive with the easy mag-netic direction (EMD) lying along h100i axis, while the K1 forTbFe2 is negative with EMD lying along h111i [3]. Thereby, the(Tb,Dy,Nd)Fe2 should be a good anisotropy compensation alloy sys-tem. Recently, the magnetostrictive properties of TbxDy0.9�xNd0.1-

Fe1.93 are reported by Jammalamadaka et al. and found theanisotropy compensation point is near x = 0.25, showing it a prom-ising pseudobinary alloy system [4].

Considerable work substituting Fe with Co has been done in aneffort to improve the magnetic and magnetostrictive properties ofthe pseudobinary (R,R0)Fe2 alloys [5–10]. It has been pointed outthat Co substitution for Fe increases the spin-reorientation

temperature of Terfenol-D [5,6] and, Co can improve the formationof Laves phase and suppress the appearance of the non-cubic phaseunder ambient condition for the alloy system containing light rareearths [7–9]. Zhai et al. [10] found that both Curie temperature andsaturation magnetization increase with the slightly increase of Cocontent for Nd0.9Tb0.1(Fe1�xCox)1.9 alloys. Recently, we found thatCo also has a positive effect on the formation of Laves phase inthe Tb1�xNdx(Fe0.8Co0.2)1.93 system [7]. Thus, in the present work,the 20 at.% Co was introduced into TbxDy0.9�xNd0.1Fe1.93 system,aiming to develop new magnetostrictive materials for applications.

In case of magnetostrictive composites, these materials are ofimportance for various applications since they possess the distinctadvantages of reducing high-frequency eddy current losses andintrinsic brittleness in comparison with monolithic alloys. In addi-tion, the 1–3 type composite (the embedded phase is connected inone direction and the second phase is connected in all three direc-tions) got more attentions for its excellent anisotropic magneto-striction [11–14]. In this work, the structure, spin configuration,magnetocrystalline anisotropy compensation, magnetic properties,and magnetostriction of TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 compoundsare investigated. Spin reorientation was observed with the differ-ent Tb/Dy ratio, subjected to the anisotropy compensationbetween Tb3+ and Dy3+ ions. The strong h111i-oriented pseudo-1–3 type epoxy/Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 composite has beenfabricated by curing under a moderate magnetic field. A largelinear anisotropic magnetostriction of about 650 ppm for the com-posite is obtained at an applied magnetic field of 6 kOe.

584 H.Y. Yin et al. / Journal of Alloys and Compounds 582 (2014) 583–587

2. Experiments

All samples of TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 (0.20 6 x 6 0.60) were prepared byarc melting the appropriate constituent metals in a high purity argon atmosphere.The purities of the constituents are 99.9wt% for Tb, Dy and Nd, and 99.8wt% for Feand Co, respectively. The ingots were sealed in an evacuated quartz tube filled withhigh-purity argon and homogenized at 670 �C for 7 days, and then furnace cooled toroom temperature (RT). X-ray diffraction (XRD) data were recorded at RT with CuKa radiation in a D/max-cA diffractometer with a graphite crystal monochromator.To prepare the magnetically aligned samples, the powdered particles of 6 150 lmand epoxy with the weight ratio of 1:2 were homogenously mixed in a plastic mold,and then placed in an electromagnet with a uniform magnetic field of 20 kOe. XRDwas implemented on the surface (perpendicular to the curing magnetic field) of thesamples, in order to study the easy magnetization direction (EMD) of the Lavesphases [14,15]. To investigate the spontaneous magnetostriction k111 of the abovecompounds, a high-precision XRD step scanning at RT was performed on powderedsamples for the (440) peak and then the effect of the Ka2 radiation was removedwith a standard method [6,16]. Temperature dependence of AC initial susceptibility,XAC, at H = 2 Oe, was measured to determine Curie temperatures TC of the com-pounds in the alloys. The linear magnetostriction was measured using standardstrain-gauge technique in parallel (k||) or perpendicular (k\) direction of appliedmagnetic fields.

As for the composites, predetermined quantities of alloy particles and epoxy,corresponding to the particles with a volume fraction 20% of the composites, werehomogeneously mixed in cubic molds of 10 � 10 � 10 mm3. The resulting slurrywas degassed under a vacuum for 30 min to eliminate air bubbles. The molds wereplaced in an electromagnet with and without a uniform magnetic field of 10 kOealong the longitudinal direction of the mold. After aligning and producing chainssimilar to aligned short-fiber, classified as ‘‘pseudo-fiber’’ configuration (pseudo-1–3 type composite) [17,18], composites were demolded. XRD and magnetostric-tion were also performed at RT.

3. Results and discussion

The XRD patterns of homogenized TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93

alloys, as examples of x = 0.20, 0.30 and 0.60, are shown in Fig. 1. Itcan be seen that all the alloys are essentially the single (Tb,Dy,Nd)(Fe,Co)2 phase with a MgCu2-type cubic structure over the wholeconcentration range investigated. All lines in the diffraction pat-terns can be indexed to the characteristics of the Laves phase.The whole X-ray reflection slightly shifts to lower Bragg angleswith increasing of Tb content, because of the increase of the latticeconstant due to the larger radius of Tb3+ ion. The indices (hkl) ofthe Laves phase are also indexed in Fig. 1.

Fig. 1. XRD patterns of the TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 alloys ((hkl) of the Lavesphase is indexed).

Temperature dependencies of the AC initial susceptibility XAC

were measured (the XAC–T curves are not shown here) to deter-mine Curie temperatures TC of the laves phase in the TbxDy0.9�x

Nd0.1(Fe0.8Co0.2)1.93 alloys, and the composition dependence of TC

is shown in Fig. 2. It can be seen that the Curie temperature in-creases from 685 K to 701 K as x is increased from 0.20 to 0.60, as-cribed to that the magnitude of exchange coupling interactionsbetween Tb and Fe/Co atoms is larger than that of Dy–Fe/Co (forTbFe2, TbCo2, DyFe2 and DyCo2, TC equals 704, 238, 635 and146 K, respectively) [2,19]. Compared with the Co-free alloy sys-tem, the 20 at.% Co substitution for Fe increases TC and extendstheir operating temperature scope with about 30 K.

X-ray diffraction patterns at RT of magnetically oriented pow-ders of TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 alloys with 0.25 6 x 6 0.45are shown in Fig. 3. As for the samples of x P 0.30, the intensityof (222) peak is strongest accompanied by the strengthened(111) and (333) peaks, which indicates the easy magnetizationdirection (EMD) lying along h111i direction in accordance withthe EMD of Tb is along h111i [4,13]. The (222) peak weakens withdecreasing Tb content of x < 0.30 and, the (311) peak turns backthe strongest one, the same situation as its polycrystalline state,suggesting that the EMD deviates from h111i. As for the sampleof x = 0.25, the (800) peak appears indicating the h100i EMDalthough the intensity for (800) peak is not the strongest. Thisincomplete h100i alignment in XRD patterns can be ascribed tothat the alloy particles with about 150 lm are not guaranteed tobe single domain particles and the curing magnetic field of20 kOe in preparation process is insufficient to provide the torqueneeded to rotate the crystallites into alignment completely [15]. Ascompared with the Co-free Tb0.25Dy0.65Nd0.1Fe1.93 compoundswhere (800) peak can not be observed [4], the 20 at.% Co substitu-tion for Fe increases the spin-reorientation temperature TSR toabove RT and slightly changes the composition for the anisotropycompensation to the Tb-rich side at RT. Clark reported that the signof anisotropy constant K1 of TbFe2 is negative while K1 is positivefor DyFe2, and the EMD of TbFe2 and DyFe2 lie along h111i andh100i, respectively [2]. Thus, the composition dependence ofEMD for TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 demonstrates the anisot-ropy compensation between Tb3+ and Dy3+ ions and compensationpoint at RT is around x = 0.30 [15,20].

The magnetostriction measurements were performed in a staticstate with a magnetic field starting from 0 to 10 kOe. The magneticfield dependence of the magnetostriction ka (= k||�k\) for theTbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 alloys is shown in Fig. 4(a). It is clearthat the saturation is not achieved for all samples. For the samples

Fig. 2. Composition dependence of Curie temperature TC of the Laves phase in theTbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 alloys.

Fig. 3. XRD patterns of the magnetically aligned TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93

powder at room temperature.

(a)

(b)

Fig. 4. (a) Magnetic field and (b) composition dependence of magnetostriction ka (=k||�k\) for the TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 alloys.

Fig. 5. Profiles of the step-scanned (440) XRD line of the Laves phase for theTb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 alloy.

H.Y. Yin et al. / Journal of Alloys and Compounds 582 (2014) 583–587 585

of 0 6 x 6 0.25, the magnetostriction ka initially reaches a negativeminimum, then increases and changes its sign with increasingmagnetic field H. This magnetostrictive character is mainly dueto the abnormal magnetostriction of DyFe2 and DyCo2, and as a re-sult of the competition between the positive magnetostriction ofDyFe2 (and TbFe2) and the negative magnetostriction of DyCo2

[2,21]. The similar tendency was also observed in the Co-substi-tuted (Dy,Pr) (Fe,B)2 system [22]. To further understand the depen-dence of magnetostriction ka on composition, the curve ka�x atdifferent applied magnetic fields is plotted in Fig. 4(b). ka decreaseswith increasing Tb content x at the same field when 0 6 x 6 0.25,then increases with a further increasing x and exhibits a peak inthe range of 0.30 < x < 0.50. The behavior is similar to the magneto-striction of Tb1�xDyxFe2 [2] and Co-doped Tb1�xHoxFe2 alloys [13],indicating that the TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 system is ananisotropy compensation system, which is consistent with theanalysis of EMD. Unlike the anisotropy compensation point nearx = 0.25 for the Co-free system reported by Jammalamadaka et al.[4], the 20 at.% Co substitution for Fe moves the point to the Tb-richside (around x = 0.30). It can be understood by that the increasingTb content increases the negative anisotropy in the Laves phaseand the Co addition increases the positive anisotropy energy [6].From the ka�x curves, magnetostriction exhibits a peak nearx = 0.40, which can be attributed to the Tb0.4Dy0.5Nd0.1(Fe0.8-

Co0.2)1.93 alloy possessing a large spontaneous magnetostrictionand a small magnetocrystalline anisotropy resulted by the com-pensation between Tb3+ and Dy3+ ions.

It is found that the EMD of compounds (x P 0.30) is lying alongthe h111i direction. Then, the step scanning of the (440) reflectionof the compounds was performed to determine the splitting causedby the magnetostriction. The XRD spectra with deduction of Ka2

with a standard method for the Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 alloyare shown in Fig. 5. The solid lines are experimental data. The dashlines are fitted XRD lines, corresponding to the pseudocubic (440)and ð4 �40Þ lines of the compound with a rhombohedral distortioncaused by the magnetostriction. The (440) split lines are consis-tent with their EMD along the h111i direction [23,24]. The dotlines result to be the sum of the two fitted lines. Themagnetostriction coefficient k111 of the Laves phase can be calcu-lated from the fitted XRD lines by using the equation [4,25]

k111 ¼ 2d440 � d440

d440 þ d440

� 1� sin h1

sin h2ð1Þ

where h1, h2 are respectively diffraction angles of the split (440)lines. It is calculated that the Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 alloypossesses a large spontaneous magnetostriction, the coefficientk111 up to about 1640 ppm, meaning that it should be a promisingcandidate and should realize the high linear magnetostriction valuefor its single-crystal situation.

An insulating matrix is essential for the high frequency applica-tion of magnetostrictive materials. The epoxy bonded 0–3 andpseudo 1–3 type Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 composites with20 vol% alloy particles were fabricated by curing without and with

(a)

(b)

586 H.Y. Yin et al. / Journal of Alloys and Compounds 582 (2014) 583–587

a magnetic field of 10 kOe, respectively. The XRD detecting direc-tion for the composite is along the rod, parallel to the curing mag-netic field. XRD patterns at RT for the composites are shown inFig. 6. It can be seen that the structure of 0–3 type composite didnot change compared with the Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93

polycrystalline alloy whose strongest peak is (311). As for thepseudo-1–3 type composite, the strongest peak is (222) accompa-nied by the strengthened (111) and (333) peaks which indicatesits EMD lying along h111i axis, similar to the magnetically alignedsample showed in Fig. 3. The magnetic field dependence of longitu-dinal magnetostriction k|| and linear anisotropic magnetostrictionka (= k|| – k\) for the composites is shown in Fig. 7. We can see thatthe pseudo-1–3 type composite has a larger magnetostriction ascompared to 0–3 composite. It is known that the magnetostrictionof a polycrystalline alloy can be described as [15]

k ¼ a � k111 þ ð1� aÞ � k100 ð2Þ

Fig. 7. The magnetic field dependence of (a) longitudinal magnetostriction k|| and(b) linear anisotropic magnetostriction ka(= k|| – k\) for the epoxy/Tb0.4Dy0.5Nd0.1

(Fe0.8Co0.2)1.93 composites.

where k111 and k100 are magnetostriction coefficient of the polycrys-talline alloy. The enhanced magnetostriction for 1–3 type would bewell understood from this formula as follow: On one hand, the the-oretical value of coefficient a for isotropy alloy is 0.60, which is thesame situation for the 0–3 composite (dispersing alloy particles inthe matrix). On the other hand, the coefficient a of 1–3 compositeshould be larger than 0.60 because of the h111i-textured particlesalong the measuring direction. Besides, k111 is larger than k100 forthe Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 alloy as well as 1–3 compositehas the chain structure, in which magnetostriction can be trans-ferred through the interaction of the neighbor particles [17]. There-fore, it would be well understood why the magnetostriction of 1–3composite is larger than that of 0–3 composite. It is noted that ahigh magnetostriction can be reached for the 1–3 type Tb0.4Dy0.5

Nd0.1(Fe0.8Co0.2)1.93 composite, that is k|| and ka up to around 390and 650 ppm at 6 kOe, respectively, which presents an excess of65% of its polycrystalline alloy. Moreover, it only contains 20 vol%alloy particles in the insulating epoxy, which make it technologicalinterest for the field of Nd-containing magnetostrictive materials. Inaddition, it is believed that the magnetostriction will be improvedwhen tailored detailedly the volume ratio and applied under a com-pressive prestress [11,12].

Fig. 6. XRD patterns of the epoxy/Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93 composites.

4. Conclusion

In conclusion, the structural, magnetic and magnetostrictiveproperties of TbxDy0.9�xNd0.1(Fe0.8Co0.2)1.93 (0.20 6 x 6 0.60) alloyshave been investigated. The composition anisotropy compensationhas been realized near x = 0.30 based on the results of XRD, EMDand magnetostriction. The EMD at RT rotates from the h100i axis(x 6 0.25) to the h111i axis (x P 0.30) with increasing Tb content,subjected to the anisotropy compensation between Tb3+ and Dy3+

ions. The Laves phase compound Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93

has a large spontaneous magnetostriction, the coefficient k111 upto about 1640 ppm. The pseudo-1–3 epoxy/composites withh111i-texture-oriented and chain structure have been fabricatedby curing at a magnetic field. A high magnetostriction, k|| and ka

(= k||�k\) up to around 390 and 650 ppm at 6 kOe, respectively,is obtained for the pseudo-1–3 epoxy/Tb0.4Dy0.5Nd0.1(Fe0.8Co0.2)1.93

composite with 20 vol% alloy particles, which can be attributed tothe large spontaneous magnetostriction k111, EMD lying alongh111i direction, the strong h111i-textured orientation and thechain structure.

Acknowledgments

This work was supported by the National Natural Science Foun-dation of China (Nos. 50801039 and 11074227), Zhejiang Province(Y4090022), Ningbo (2012A610054), and K.C. Wong Magna/Educa-tion Fund in Ningbo University. The authors gratefully acknowl-edge the help of Professor Zhidong Zhang, Dr. Weijun Ren andDr. Yong Wang (Institute of Metal Research, Chinese Academy ofSciences) in the measurement of partial samples.

References

[1] N.C. Koon, C.M. Williams, B.N. Das, J. Magn. Magn. Mater. 100 (1991) 173.[2] A.E. Clark, in: E.P. Wohlfarth (Ed.), Ferromagnetic Materials, vol. 1, North-

Holland, Amsterdam, 1980, p. 531.

H.Y. Yin et al. / Journal of Alloys and Compounds 582 (2014) 583–587 587

[3] Z.J. Guo, S.C. Busbridge, B.W. Wang, Z.D. Zhang, X.G. Zhao, D.Y. Geng, J. Appl.Phys. 86 (1999) 6310.

[4] S.N. Jammalamadaka, G. Markandeyulu, K. Balasubramaniam, Appl. Phys. Lett.97 (2010) 242502.

[5] A.E. Clark, J.P. Teter, M. Wun-Fogle, J. Appl. Phys. 69 (1991) 5771.[6] J.J. Liu, W.J. Ren, D. Li, N.K. Sun, X.G. Zhao, J. Li, Z.D. Zhang, Phys. Rev. B 75

(2007) 064429.[7] H.Y. Yin, J.J. Liu, R. Wang, X.C. Liu, N.K. Sun, Mater. Chem. Phys. 134 (2012)

1102.[8] J.J. Liu, W.J. Ren, S.L. Chen, D. Li, J. Li, X.G. Zhao, W. Liu, Z.D. Zhang, J. Phys. D 39

(2006) 243.[9] B.W. Wang, Z.J. Guo, Z.D. Zhang, X.G. Zhao, S.C. Busbridge, J. Appl. Phys. 85

(1999) 2805.[10] L. Zhai, Y.G. Shi, S.L. Tang, Y. Wang, L.Y. Lv, Y.W. Du, J. Alloys Comp. 487 (2009)

34.[11] L. Sandlund, M. Fahlander, T. Cedell, A.E. Clark, J.B. Restorff, J. Appl. Phys. 75

(1994) 5656.[12] T.A. Duenas, G.P. Carman, J. Appl. Phys. 87 (2000) 4696.

[13] J.J. Liu, R. Wang, H.Y. Yin, X.C. Liu, J. Du, J. Appl. Phys. 110 (2011) 073915.[14] J.J. Liu, Z.B. Pan, P.Z. Si, J. Du, Appl. Phys. Lett. 103 (2013) 042406.[15] J.J. Liu, H.Y. Ying, X.C. Liu, P.Z. Si, J. Alloys Comp. 509 (2011) 8207.[16] V.H. Babu, G. Markandeyulu, A. Subrahmanyam, J. Magn. Magn. Mater. 320

(2008) 990.[17] X.K. Lv, S.W. Or, W. Liu, X.H. Liu, Z.D. Zhang, J. Phys. D 42 (2009) 035002.[18] F. Yang, C.M. Leung, S.W. Or, W. Liu, X.K. Lv, Z.D. Zhang, J. Alloys Comp. 509

(2011) 4954.[19] K.H.J. Buschow, Rep. Prog. Phys. 40 (1977) 1179.[20] W.J. Ren, J.J. Liu, D. Li, W. Liu, X.G. Zhao, Z.D. Zhang, Appl. Phys. Lett. 89 (2006)

122506.[21] A.D. Moralt, D. Melville, J. Phys. F: Met. Phys. 5 (1975) 1767.[22] W.J. Ren, D. Li, Y.C. Sui, W. Liu, X.G. Zhao, J.J. Liu, J. Li, Z.D. Zhang, J. Appl. Phys.

99 (2006) 08M701.[23] A.E. Clark, J.R. Cullen, K. Sato, AIP Conf. Proc. 24 (1975) 670.[24] J.J. Liu, P.Z. Si, W.S. Zhang, X.C. Liu, J. Alloys Comp. 474 (2009) 9.[25] E. Gratz, A. Lindbaum, A.S. Markosyan, H. Mueller, A.Y. Sokolov, J. Phys.:

Condens. Matter. 6 (1994) 6699.