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Journal of Crystal Growth 310 (2008) 2613–2616

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Growth and magneto-optical properties of NaTb(WO4)2

Jingjing Liu, Feiyun Guo, Bin Zhao, Naifeng Zhuang, Yanping Chen,Zhaoping Gao, Jianzhong Chen�

College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou 350002, PR China

Received 6 November 2007; received in revised form 19 December 2007; accepted 24 December 2007

Communicated by M. Roth

Available online 9 January 2008

Abstract

Sodium terbium tungstate (NaTb(WO4)2) single crystal with dimension + 25mm� 30mm and a good optical quality was grown by

Czochralski method. The transmission spectrum was measured in the visible and near-infrared region at room temperature. The specific

Faraday rotation of single crystal was measured at room temperature in 532, 633, and 1064 nm wavelength. The Verdet constant and

magneto-optical figure of merit was investigated. Comparing to the magneto-optical figure of merit and Verdet constant for TGG, the

NaTb(WO4)2 have larger magneto-optical figure of merit and larger Verdet constant. It indicates that NaTb(WO4)2 crystal can be a

promising magneto-optical material in visible region.

r 2008 Elsevier B.V. All rights reserved.

PACS: 78.20.Ls; 81.10.Fq

Keywords: A2. Czochralski method; B1. Tungstates; B2. Magneto-optical properties

1. Introduction

With the rapid advance in optic communication andoptical measurement technology, the research and applica-tion of non-reciprocal magneto-optical devices becomemore and more important, especially the demand foroptical Faraday devices at wavelengths of 400–1100 nm,where conventional Bi-substituted yttrium iron garnets(Bi:YIG) are not applicable because of their poortransparency. For these devices, both large Faradayrotation angles and high transmittance are important.Terbium aluminum garnet (TAG) and terbium galliumgarnet (TGG) are thought to be the better materials forsuch requirements among transparent magnetic materialsbecause of their large Verdet constant [1,2] and goodtransmittance [3]. However practically applicable TAGsingle crystals had not been obtained by Czochralski

e front matter r 2008 Elsevier B.V. All rights reserved.

rysgro.2007.12.065

ing author. Tel.: +86591 87893223;

893237.

ess: j.z.chen@fzu.edu.cn (J. Chen).

method because of their incongruent melting nature [4] andit should be noted that relatively high evaporation ofGa2O3 from the melt should be responsible for thedeviations from stoichiometry occurring during the TGGcrystal growth [5].Optical properties of rare-earth ions in crystalline and

glassy environments are still the subject of intense studiesin recent years; especially Tb3+-doped crystal or glass[6–9]. Tb3+ ion exhibits a strong paramagnetism due to thetransition between 4f8-4f75d [10]. NaRE(WO4)2 (Ln ¼La–Lu, Y, Bi) have been reported to be good host materialfor solid-state lasers [11,12]. Most of these crystals have atetragonal symmetry with the structure of the scheeliteCaWO4 [13]. Na+ and Ln3+ ions share almost randomlythe same lattice sites [14,15]. Moreover, NaRE(WO4)2crystals were reported as congruently melting whenRE=Y, La–Er, and as incongruently melting whenRE=Tm, Yb, and Lu [16]. In this work, we report thegrowth, spectral and magneto-optical properties of sodiumterbium tungstate (NaTb(WO4)2) which is a member ofNaRE(WO4)2 double tungstate.

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Fig. 2. Crystal of NaTb(WO4)2.

J. Liu et al. / Journal of Crystal Growth 310 (2008) 2613–26162614

2. Experimental procedure

2.1. Crystal growth

High-purity Na2CO3 and WO3 (4N) and Tb4O7 (5N)were mixed stoichiometrically, and pressed into tablets;then, the tablets were sintered at 900 1C for 10 h in air. Thechemical reaction formula is as follows:

2Tb4O7! 4Tb2O3 þO2m;

Na2CO3 þ Tb2O3 þ 4WO3 ! 2NaTb ðWO4Þ2 þ CO2m:

The DSC measurement was performed up to 1400 1C ata heating rate of 10 1C/min using a SDT Q600 DifferentialThermal Analyzer. The result of DSC analysis shows thatNaTb(WO4)2 compound is congruently melt about at1235 1C, as shown in Fig. 1.

The NaTb(WO4)2 crystal was grown by the Czochralskimethod, a platinum crucible of 55mm in diameter wasutilized to grow the single crystal with radio frequency(RF) induction heating. The crystal was grown using a seedwith [0 0 1] orientation. The pulling and rotation rates were1–1.4mm/h and 10–15 rpm, respectively. Finally, NaTb(WO4)2 crystal with dimension +25mm� 30mm wasobtained, as shown in Fig. 2, which is transparent andcrack free.

2.2. X-ray powder diffraction

The X-ray powder diffraction data were obtained using acomputer-automated diffractometer (Rigaku D/max-3c)equipped with Cu Ka radiation (l ¼ 1.54056 A) at roomtemperature. The data of X-ray powder diffraction wasindexed by computer program.

2.3. Transmission spectrum

The grown NaTb(WO4)2 single crystal was cut along/0 0 1S plane directed by X-ray diffraction, and then

Fig. 1. DSC curve of NaTb(WO4)2 compound.

Fig. 3. Schematic diagram of the magneto-optical test system. 1: Laser;

2: Polarizer; 3: Electromagnet; 4: Crystal sample; 5: Analyzer; 6: Optical

powermeter; 7: Teslameter; 8: Supply transformer; 9: Rotation angular

inspector.

ground and polished carefully to about 5mm thicknessfor spectral measurement. The transmission spectrumwas measured using a Perkin-Elmer Lambda 900 UV–vis–NIR spectrophotometer in the wavelength range of400–1500 nm at room temperature.

2.4. Faraday rotation angle

The Faraday rotation angle was measured at roomtemperature using the magnet-optical test system, whichwas assembled by us. Fig. 3 is the schematic diagram of

ARTICLE IN PRESSJ. Liu et al. / Journal of Crystal Growth 310 (2008) 2613–2616 2615

the magneto-optical test system. In this work a laserof 532, 633, and 1064 nm was used as the sources of probebeam.

Fig. 4. X-ray power diffraction of NaTb(WO4)2 crystal at room

temperature.

400 600 800 1000 1200 1400 160040

50

60

70

80

T%

wavelength(nm)

Fig. 5. Transmission spectrum of NaTb(WO4)2 crystal at room temperature.

Table 1

Magneto-optical properties of NaTb(WO4)2 and TGG crystal

Crystal wavelength NaTb(WO4)2

532 nm 6

Optic absorption coefficient (cm�1) 0.51

Verdet constant (rad/mT) �211 �

Faraday rotation (1/cm) �143 �

Magneto-optical figure of merit (1/dB) (no coating) 64.56

3. Results and discussion

3.1. Lattice parameters

The X-ray powder diffraction pattern of NaTb(WO4)2crystal is shown in Fig. 4. And the unit cell parameters weredetermined using an X-pert Plus program. The resultshows that the crystal NaTb(WO4)2 belong to tetragonalsystem and the unit cell parameters: a ¼ b ¼ 0.5237 nm,c ¼ 1.1356 nm, V ¼ 0.3114 nm3.

3.2. Absorption coefficient

Fig. 5 shows the transmission spectrum of NaTb(WO4)2crystal. The value of optical absorption coefficienta in the wavelength of 532 and 633 nm in NaTb(WO4)2crystal is about 0.51 and 0.46 cm�1, respectively, whilethat of TGG (Tb3Ga5O12) crystal is about 0.68 and0.52 cm�1.

3.3. Magneto-optical figure of merit

Magneto-optical figure of merit, defined by the ratio ofFaraday rotation angle and optical absorption loss, cangenerally represent the magneto-optical properties ofmaterials. The Faraday rotation of NaTb(WO4)2 in the532 nm wavelength and 633 nm wavelength is �143 and�1051/cm, respectively. Magneto-optical figure of merit ofNaTb(WO4)2 calculated from specific Faraday rotationand optical absorption coefficient is 64.561/dB in 532 nmwavelength and 52.561/dB in 633 nm wavelength, largerthan that of TGG. For contrasting, the main magneto-optical properties of NaTb(WO4)2 crystal and TGG[4,17,18] crystal were given in Table 1.

4. Conclusion

The NaTb(WO4)2 crystal has been grown successfully bythe Czochralski method. The crystal had a wide transmis-sion in the optical range of 500–1500 nm. And it had largerspecific Faraday rotation, larger magneto-optical figure ofmerit than that of TGG. So the NaTb(WO4)2 can be apromising material for magneto-optical devices in visibleregion.

TGG

33nm 1064 nm 532 nm 633 nm 1064nm

0.46 0.44 0.68 0.52 0.50

155 �52 �190 �134 �40

105 �35 �129 �91 �27

52.56 18.32 44 40.3 12.4

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Acknowledgments

The research was supported by the Natural ScienceFoundation of Fujian Province (2007J0148) and NationalNatural Science Foundation of China (50772023).

References

[1] C.B. Rubinstein, L.G. Van Uitert, W.H. Grodkiewicz, J. Appl. Phys.

35 (1964) 3096.

[2] M.Y.A. Raja, D. Allien, W. Sisk, Appl. Phys. Lett. 67 (1995) 2123.

[3] B. Sugg, H. NUrge, B. Faust, E. Ruza, R. NiehUser, H.-J. Reyher,

R.A. Rupp, L. Aclerman, Opt. Matter 4 (1995) 354.

[4] S. Ganschow, D. Klimm, P. Reiche, R. Uecker, Cryst. Res. Technol.

34 (1999) 615.

[5] C. Robert Linares, Solid States Commun. 2 (1964) 229.

[6] H. Ebendorff-Heidepriem, D. Ehrt, Opt. Mater. 15 (2000) 7.

[7] H. Hosono, T. Kinoshita, H. Kawazoe, M. Yamazaki, Y. Yamamo-

to, N. Sawanobori, J. Phys. Condens. Matter 10 (1998) 9541.

[8] Jiang Yasi, M.J. Myers, D. Rhonehouse, Chin. J. Lasers (EE) 1 (6)

(1992) 513.

[9] Tanaka Katsuhisa, Hirao Kazuyuki, Soga Naohiro, Jpn. J. Appl.

Phys. 34 (1995) 4825.

[10] Naruhito Sawanobori, Naoko Mori, et al., New Glass 18 (2003) 5.

[11] A.A. Kaminskii, N.R. Agamalyan, L.P. Kozeeva, V.F. Nesterenko,

A.A. Ravlyuk, Phys. Status Sol. A 75 (1983) K1.

[12] A.A. Kaminskii, Laser Crystals. Their Physics and Properties,

second ed., vol. 14, Springer, Berlin, Heidelberg, 1990 (Springer

Ser. Opt. Sci.).

[13] L.D. Ivanova, J. Struct. Chem. 7 (1966) 108.

[14] Junhai Liu, Jose.Marıa Cano-Torres, Fatıma Esteban-Betegon, Opt.

Laser Technol. 39 (2007) 558.

[15] G.M. Kuz’micheva, D.A. Lis, K.A. Subbotin, V.B. Rybakov,

E.V. Zharikov, J. Crystal Growth 275 (2005) e1835.

[16] E.Ya. Rode, V.N. Karpov, M.M. Ivanova, Russ. J. Inorg. Chem. 16

(1971) 905.

[17] M. Yasin Akhtar Raja, David Allen, Wade Sisk, Appl. Phys. Lett. 67

(1995) 2123.

[18] Weijing Zhang, Feiyun Guo, Jianzhong Chen, J. Crystal Growth 306

(2007) 195.