- Email: [email protected]
Improving characteristic of Faraday effect based on the Tm3+ doped terbium gallium garnet single crystal
Journal of Alloys and Compounds 661 (2016) 62e65
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Improving characteristic of Faraday effect based on the Tm3þ doped terbium gallium garnet single crystal Zhe Chen*, Lei Yang, Yin Hang, Xiangyong Wang Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, No. 390, Qinghe Road, Jiading District, Shanghai 201800, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 September 2015 Received in revised form 29 October 2015 Accepted 22 November 2015 Available online 2 December 2015
Highly transparent Tm3þ doped terbium gallium garnet single crystal was grown by the Czochralski(Cz) method for magneto-optical applications. The single-crystal X-ray diffraction confirms that the compound crystallize in the cubic systems with the structure a ¼ b ¼ c ¼ 1.2338 nm. The temperature dependence of the magnetic susceptibility indicates that the Tm:TGG crystal exhibits paramagnetic behavior over the experimental temperature-range 10e300 K. Transmittance spectra and the Faraday rotation have been investigated, which demonstrates that the as-grown crystal shows a high visible transparency and yields a lager Faraday rotation comparable to that of TGG crystal. The increasing of the Verdet constant at measured wavelength and high thermal property show the superior characteristics of Tm3þ doped TGG compared to the pure TGG, indicating that it has significant development for magnetoactive materials used in Faraday devices at visible and near-infrared regions (VIS-NIR). © 2015 Elsevier B.V. All rights reserved.
Keywords: Magneto-optical properties Optical material Faraday effect Magnetic susceptibilities
1. Introduction With continuous development of high-power laser-diodes and high-power fiber-lasers operating at VIS-NIR [1,2], Faraday isolators (FIs) used for such region gain great development in recent years. FIs are fundamental components used in advanced optical communications system to prevent harmful back-reflections [3,4], and to eliminate parasitic oscillations in amplifier systems or frequency instabilities in laser diodes [5,6]. As the core part of the FIs, the Faraday rotator obtained by magneto-optic materials primarily determines the performance of FIs. Yttrium-iron garnet, Y3Fe5O12 (YIG) and Bi doped YIG materials with high transparency in the infrared regions is employed and characterized by a very large Verdet constant (2200 and 1700 rad/Tm at 1310 and 1550 nm, respectively) [7e10]. Terbium gallium garnet(Tb3Ga5O12, TGG) is thought to be a suitable material for such requirement among transparent magnetic materials because of its favorable growth characteristics and high transmittance. TGG can be grown large size single crystal for its congruent melting nature in comparison with TAG [11e13], however, as the rapid development of visible light communications the demand of
* Corresponding author. E-mail address: [email protected] (Z. Chen). http://dx.doi.org/10.1016/j.jallcom.2015.11.162 0925-8388/© 2015 Elsevier B.V. All rights reserved.
FIs operated at VIS-NIR are rapidly increasing, while the conventional TGG crystals are not practical due to its low V (134radT1m1 at 632.8 nm) compared to the Tb3Al5O12, which meas that FIs needs a higher magnetic field intensity or larger length of the crystal to eliminate the back-reflection, increasing the instability of high power laser systems caused by some thermal-optics effect [14]. Some researchers have found that the quantum based superexchange interaction between Tb3þ and other paramagnetic Re3þ ions can occur, greatly enhancing the Faraday effect. Recently, the study of Ce3þ doped TAG ceramic has 199.55radT1m1 at 632.8 nm of V, 16% larger than that of TAG [15]. {Tb3}[Sc1.95Lu0.05](Al3)O12 (TSLAG) single crystal having a increment of 20% of V compared to TGG dues to the doping of Sc3þ,Lu3þ,Al3þ ions [16]. Some fluoride single crystals with high concentration of efficient paramagnetic Re3þ ions in UV-VIS region shows excellent magneto-optical properties [17]. So in this letter, the current investigation centers on producing larger Faraday effect material based on TGG single crystal owing to its congruently nature compared with TAG. The magneto-optical properties in TGG arise from the transition 4f8/4f75 d1 of single Tb3þ ion, However, researchers have found that more than one single paramagnetism ions in garnets can remarkably enhance the magneto-optical property (Ce3þ, Pr3þ, Nd3þ doped TGG crystals [18e20] with 20e30% larger of Verdet constant compared to that of TGG). On the other hand, Tm3þ ion has been pointed out to show a
Z. Chen et al. / Journal of Alloys and Compounds 661 (2016) 62e65
63
large effective magnetic moment among the rare earth ions, Thus we suspect that a lager Faraday rotation angle of Tm3þ doped terbium gallium garnet can be obtained due to the strong magnetic moment of Tb3þ-Tm3þ super interactions. In this work, we report the growth of Tm3þ doped TGG crystal by Czochralski method for the first time, as well as its magneto-optical characteristic.
program. The result shows that the crystal belongs to the cubic system and its lattice parameters are a ¼ b ¼ c ¼ 1.2338 nm,a slightly smaller than that of pure TGG. It may be the reason that the radius of Tm3þ is smaller than of Tb3þ. As the segregated dopant disperses into melt homogenously, the solute concentration in the crystal CS at growth interface would change with the solid fraction of the grown crystal by:
2. Experimental procedure
Cs ¼ C0 keff ð1 gÞkeff 1
High-purity Tb4O7, Tm2O3,Ga2O3 (5N) chemicals were mixed according to the designed Tb2.98Tm0.02Ga5O12, then the mixture of powders (1e2% excess of Ga2O3) were pressed to sheet and sintered for 12 h at 1200e1400 C. Such formed materials were crushed, remixed and sintered again at 1200e1400 C for 24 h. Finally, we obtained polycrystalline materials. The crystal was grown by the Cz method in a iridium crucible with radio frequency (RF) induction heating. After that crystal growth was carried out under high purity N2 (99.99%) atmosphere. It was grown in the <111 > orientation at a pulling rate of 1.0 mm/h and a rotating rate of 10e15 rpm. Finally, Tb3-xTmxGa5O12 crystal was obtained. The transmission spectrum were measured using a PerkineElmer Lambda 900 UV-VIS-NIR spectrophotometer (United States) in transmission mode over the wavelength range of 300 nm2000 nm. The X-ray powder diffraction measurement was carried out by the Ultima IV (Rigaku, Japan). A schematic of the experimental is setup for investigating the Faraday effects. A light sources (Xe-lamp and monochromator) passed through the sample located between a pair of Glan laser prisms. The transmitted light power was measured using a power meter. A polarization plane of laser light was rotated by the Faraday effect because of the magnetic field. Commercial TGG crystal (CASTECH) utilized for the calibration. All the measurements were performed at room temperature.
(1)
where C0 is the initial solute concentration, and keff is effective segregation coefficient. In the Fig. 2, the cation distribution of Tm3þ ion as a function of the solid fraction is shown, as g increase, Tm3þ concentration in the crystal increases and Ga3þ concentration decreases, whereas Tb3þ concentration seems not to depend on the solid fraction. The distribution coefficient keff of Tm3þ is nearly 0.50. 3.2. Transmittance spectrum Fig. 3 shows the transmittance spectrum of Tm: TGG crystal. It is important for a good magneto-optical material to have a low absorption loss in some specific wavelength range, such as 532, 633 and 1064 nm. There are two absorption bands centered at around 660, 760 nm, which correspond to the transitions starting from the 3 H6 ground state of Tm3þ to higher levels 3F2,3, 3H4, respectively, while absorption band centered at 486 nm is mainly related to the energy level transition 7F6-5D4 of Tb3þ. It can be seen that Tm:TGG has good optical transparency which is around 80% in VIS-NIR. This parameter is very important for FIs applications, since the use of lengthy crystals requires minimizing optical losses. So the Tm:TGG crystal can be applied as a magneto-optical material in VIS-NIR FIs devices.
3. Results and discussion
3.3. Magnetic susceptibility
3.1. Structural analysis and phase stability
The magnetic susceptibility results of Tm:TGG are shown in Fig. 4. The c (T) decreases monotonously without any magnetic transition over the temperature range from 10 to 300 K under a constant magnetic field of 0.01 T. The inset of Fig. 4 indicates the reciprocal of c(T), which exhibits a linear dependence on T down to 10 K at least. The linear part of the reciprocal of c(T) can be described by the following Curie-Weiss equation which is defined as c ¼ C/(Teqp), where C is the Curie constant and qp is the Weiss temperature. The effective magnetic moment and CurieeWeiss
The Tb3-xTmxGa5O12 crystal which is shown in the insert of Fig. 1 was ground into powder and its X-ray powder diffraction pattern was shown in Fig. 1. Compared with the JCPDS standard card, the XRD powder diffraction pattern of doped crystal is agree well with the standard patterns of TGG crystal(JCPDS 88e0575) without any impurities peaks. The result indicates that the Tm3þ ion does not influence the crystal structure. The unitecell parameters were determined with the help of X Pert High Score Plus computer
Fig. 1. X-ray powder diffraction patterns of the Tm:TGG, Inset: Tm:TGG crystal was obtained by the Cz method.
Fig. 2. The Tm3þ distribution as a function of the solid fraction in the Tm:TGG crystal.
64
Z. Chen et al. / Journal of Alloys and Compounds 661 (2016) 62e65
Fig. 3. The transmission spectra of Tm:TGG crystal at measured wavelength.
Fig. 5. Faraday rotation of Tm:TGG crystal in different wavelengths at room temperature.
the magnetic susceptibility c as follows:
V¼
Fig. 4. The temperature dependence of the mass susceptibility of Tm:TGG crystal. Inset: inverse magnetic susceptibility versus temperature (H ¼ 0.01T).
temperature of Tm:TGG crystal are 9.78mB and 3.1K respectively. The temperature dependence of the magnetic susceptibility indicates that the Tm:TGG crystal exhibits paramagnetic behavior over the experimental temperature-range 10e300 K and the higher magnetic moment of Tb3þ ion may indicate that the magnetic ion in the Tm:TGG crystal are affected by the crystal field to some extent.
4p2 n2 c X Cij ij 2 gmB ch n nij2
(2)
Whereas n is the frequency of the incident light, nij is the transition frequency between electronic states, Cij is the transition factor, mB is the Bohr magneton, c is probability of this, g is the Lande the velocity of light, and h is the Planck constant. The experimental data are described by a single electronic transition, and the Verdet constant dispersion is given as a function E , whereas E of the wavelength l in simplified form as: V ¼ l2 l 2 0 includes all the constant terms, and l0 is the transition wavelength, which is associated with the electronic transition of paramagnetic RE ions. The results of the FR measurements are displayed in Fig. 6. The curves for Tm:TGG and TGG are very close to each other as the wavelength increased, while the values for Tm:TGG being much higher in the 400e1500 nm. It can be seen that Tm:TGG possesses a higher V value, with an increment of more than 20% independently of the considered wavelength in comparison with the reference TGG. The measured Verdet constants at wavelength of 532, 633, 830, 1064 and 1330 nm are 256.8, 178.6, 102.3, 60.2, 26.3 rad∕Tm, respectively, obviously larger than that of pure TGG. It can be
3.4. Magneto-optical characteristic For paramagnetic materials, the Faraday rotation qF is linear ratio to magnetic induction intensity B when the length of sample L is fixed. There exists a linear relationship between the Faraday rotation of Tm:TGG crystal and magnetic field in the range of 0e1.2 T at different wavelengths, as shown in Fig. 5. It could be concluded that Tm:TGG crystal belongs to pure paramagnetic substance at room temperature basing on the Faraday rotation dependence on an external magnetic field. The Faraday rotation of Tm:TGG crystal is close to 165 /cm in the 532 nm wavelength at 1.2T, almost 25% higher than that of TGG. This result confirm that the doping of Tm3þ ion significantly enhance the magneto-optical property in the garnet crystal. The FR of paramagnetic RE ions has been described by van Vleck-Hebb [17]. From quantum-mechanical considerations they deduced that the V constant dispersion is directly proportional to
Fig. 6. Verdet constant dispersion of Tm:TGG in comparison with that of TGG.
Z. Chen et al. / Journal of Alloys and Compounds 661 (2016) 62e65
65
7.0Wm1K1, dropping to nearly 4.2Wm1K1 at 500 C. The LIDT of measured was about 13.68J/cm2, shown in the Fig. 8. The LIDT value of Tm:TGG is almost same as the pure TGG. These results further confirm the high quality of the Tm:TGG crystal and its further application in the high power Faraday devices. 4. Conclusion
Fig. 7. The thermal conductivity of Tm:TGG compared with TGG crystal.
In conclusion, the presented results show the superior properties of Tm:TGG in comparison with TGG from any point of view related with FIs. Tm:TGG has more favorable growth characteristics and the increase of at least 20% in the Verdet constant is very significant, giving the huge possibility to reduce the intensity of the necessary magnetic fields, especially in the VIS-NIR. The Tm:TGG crystal exhibit paramagnetic behavior down to 10K. The measured thermal conductivity and LIDT features of Tm:TGG clearly indicate that this crystal is a promising magneto-optical material for highpower FIs applications. Tm:TGG has a high potential to substitute commercial TGG crystals used in FIs in the IR region (below 1100 nm) and more especially in the VIS. Acknowledgment This work was supported by Nature Science Foundation of China (Nos.51472257). References
Fig. 8. The laser induced damage threshold of the Tm:TGG at 1064 nm.
explained by that the magnetization depends on the splitting of the ground configuration induced by the spineorbit (SO) interaction, crystal field (CF), exchange interaction and external magnetic field. It should be emphasized that the exchange interaction between Tb3þ and Tm3þ ions, although much smaller, will have effects under some conditions in paramagnetic gallium garnet. 3.5. Thermal conductivity and LIDT measurement Since the thermal management is a very important point in high power laser system, thermal conductivity (Fig. 7) has been measured for Tm:TGG and TGG crystal. The curves of both are very close to each other, while the Tm:TGG being slightly lower in comparison with the reference TGG at the measured temperature. The thermal conductivity of Tm:TGG at room temperature was
[1] M.A. Kagan, E.A. Khazanov, Appl. Opt. 43 (2004) 6030. [2] R. Yasuhara, S. Tokita, J. Kawanaka, T. Kawashima, H. Kan, H. Yagi, H. Nozawa, T. Yanagitani, Y. Fujimoto, H. Yoshida, M. Nakatsuka, Opt. Express 15 (2007) 11255. [3] T. Nakanishi, M. Maeda, A. Kawashima, S. Kamiya, K. Fushimi, K. Fujita, K. Tanaka, Y. Hasegawa, J. Alloys Comp 562 (2013) 123. [4] R. Lisiecki, W. Ryba-Romanowski, P. Solarz, A. Strze˛p, M. Berkowski, J. Alloys Comp. 582 (2014) 208. [5] S. Banerjee, K. Ertel, P.D. Mason, P.J. Phillips, M. Siebold, et al., Opt. Lett. 37 (2012) 2175. [6] D. Zheleznov, A. Starobor, O. Palashov, C. Chen, S. Zhou, Opt. Express 22 (2014) 2578. [7] N. Rajamanickam, R.N. Mariammal, S. Rajashabala, K. Ramachandran, J. Alloy Compd. 614 (2014) 151. [8] Y.J. Wua, H.P. Fua, R.Y. Honga, Y. Zhengd, D.G. Weie, J. Alloy Compd. 470 (2009) 497. [9] G.J. Chen, H.M. Lee, Y.S. Chang, Y.J. Lin, Y.L. Chai, J. Alloys Compd. 388 (2005) 297. [10] A. Hasanpour, M. Mozaffari, J. Amighian, H. Richert, A. Lorenz, M. Lindner, P.G. Ornert, H. Heegn, J. Magn. Magn. Mater 317 (2007) 41. [11] J.J. Liu, F.Y. Guo, B. Zhao, N.F. Zhuang, Y.P. Chen, Z.P. Gao, J.Z. Chen, J. Cryst. Growth 310 (2008) 2613. [12] H.L. Zhu, D.L. Jin, L.M. Zhu, H. Yang, K.H. Yao, Z.Q. Xi, J. Alloy Compd. 464 (2008) 508. [13] V. Vasyliev, E.G. Villora, M. Nakamura, Y. Sugahara, K. Shimamura, Opt. Express 20 (2012) 14460. [14] D. Zheleznov, A. Starobor, O. Palashov, H. Lin, S. Zhou, Opt. Lett. 39 (2014) 2183. [15] C. Chen, S. Zhou, H. Lin, Q. Yi, Appl. Phys. Lett. 101 (2012) 131908. [16] K. Shimamura, T. Kito, E. Castel, et al., Cryst. Growth Des. 10 (2010) 3466. [17] V. Vasyliev, P. Molina, M. Nakamura, E.G. Víllora, K. Shimamura, Opt. Mater 33 (2011) 1710. [18] Z. Chen, Y. Hang, L. Yang, J. Wang, X.Y. Wang, et al., Opt. Lett. 40 (2015) 820. [19] Z. Chen, L. Yang, Y. Hang, J. Wang, X.Y. Wang, et al., Opt. Mater 47 (2015) 39. [20] Z. Chen, Y. Hang, L. Yang, J. Wang, X.Y. Wang, et al., Mater. Lett. 145 (2015) 171.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Improving characteristic of Faraday effect based on the Tm3þ doped terbium gallium garnet single crystal Zhe Chen*, Lei Yang, Yin Hang, Xiangyong Wang Key Laboratory of Materials for High Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, No. 390, Qinghe Road, Jiading District, Shanghai 201800, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 September 2015 Received in revised form 29 October 2015 Accepted 22 November 2015 Available online 2 December 2015
Highly transparent Tm3þ doped terbium gallium garnet single crystal was grown by the Czochralski(Cz) method for magneto-optical applications. The single-crystal X-ray diffraction confirms that the compound crystallize in the cubic systems with the structure a ¼ b ¼ c ¼ 1.2338 nm. The temperature dependence of the magnetic susceptibility indicates that the Tm:TGG crystal exhibits paramagnetic behavior over the experimental temperature-range 10e300 K. Transmittance spectra and the Faraday rotation have been investigated, which demonstrates that the as-grown crystal shows a high visible transparency and yields a lager Faraday rotation comparable to that of TGG crystal. The increasing of the Verdet constant at measured wavelength and high thermal property show the superior characteristics of Tm3þ doped TGG compared to the pure TGG, indicating that it has significant development for magnetoactive materials used in Faraday devices at visible and near-infrared regions (VIS-NIR). © 2015 Elsevier B.V. All rights reserved.
Keywords: Magneto-optical properties Optical material Faraday effect Magnetic susceptibilities
1. Introduction With continuous development of high-power laser-diodes and high-power fiber-lasers operating at VIS-NIR [1,2], Faraday isolators (FIs) used for such region gain great development in recent years. FIs are fundamental components used in advanced optical communications system to prevent harmful back-reflections [3,4], and to eliminate parasitic oscillations in amplifier systems or frequency instabilities in laser diodes [5,6]. As the core part of the FIs, the Faraday rotator obtained by magneto-optic materials primarily determines the performance of FIs. Yttrium-iron garnet, Y3Fe5O12 (YIG) and Bi doped YIG materials with high transparency in the infrared regions is employed and characterized by a very large Verdet constant (2200 and 1700 rad/Tm at 1310 and 1550 nm, respectively) [7e10]. Terbium gallium garnet(Tb3Ga5O12, TGG) is thought to be a suitable material for such requirement among transparent magnetic materials because of its favorable growth characteristics and high transmittance. TGG can be grown large size single crystal for its congruent melting nature in comparison with TAG [11e13], however, as the rapid development of visible light communications the demand of
* Corresponding author. E-mail address: [email protected] (Z. Chen). http://dx.doi.org/10.1016/j.jallcom.2015.11.162 0925-8388/© 2015 Elsevier B.V. All rights reserved.
FIs operated at VIS-NIR are rapidly increasing, while the conventional TGG crystals are not practical due to its low V (134radT1m1 at 632.8 nm) compared to the Tb3Al5O12, which meas that FIs needs a higher magnetic field intensity or larger length of the crystal to eliminate the back-reflection, increasing the instability of high power laser systems caused by some thermal-optics effect [14]. Some researchers have found that the quantum based superexchange interaction between Tb3þ and other paramagnetic Re3þ ions can occur, greatly enhancing the Faraday effect. Recently, the study of Ce3þ doped TAG ceramic has 199.55radT1m1 at 632.8 nm of V, 16% larger than that of TAG [15]. {Tb3}[Sc1.95Lu0.05](Al3)O12 (TSLAG) single crystal having a increment of 20% of V compared to TGG dues to the doping of Sc3þ,Lu3þ,Al3þ ions [16]. Some fluoride single crystals with high concentration of efficient paramagnetic Re3þ ions in UV-VIS region shows excellent magneto-optical properties [17]. So in this letter, the current investigation centers on producing larger Faraday effect material based on TGG single crystal owing to its congruently nature compared with TAG. The magneto-optical properties in TGG arise from the transition 4f8/4f75 d1 of single Tb3þ ion, However, researchers have found that more than one single paramagnetism ions in garnets can remarkably enhance the magneto-optical property (Ce3þ, Pr3þ, Nd3þ doped TGG crystals [18e20] with 20e30% larger of Verdet constant compared to that of TGG). On the other hand, Tm3þ ion has been pointed out to show a
Z. Chen et al. / Journal of Alloys and Compounds 661 (2016) 62e65
63
large effective magnetic moment among the rare earth ions, Thus we suspect that a lager Faraday rotation angle of Tm3þ doped terbium gallium garnet can be obtained due to the strong magnetic moment of Tb3þ-Tm3þ super interactions. In this work, we report the growth of Tm3þ doped TGG crystal by Czochralski method for the first time, as well as its magneto-optical characteristic.
program. The result shows that the crystal belongs to the cubic system and its lattice parameters are a ¼ b ¼ c ¼ 1.2338 nm,a slightly smaller than that of pure TGG. It may be the reason that the radius of Tm3þ is smaller than of Tb3þ. As the segregated dopant disperses into melt homogenously, the solute concentration in the crystal CS at growth interface would change with the solid fraction of the grown crystal by:
2. Experimental procedure
Cs ¼ C0 keff ð1 gÞkeff 1
High-purity Tb4O7, Tm2O3,Ga2O3 (5N) chemicals were mixed according to the designed Tb2.98Tm0.02Ga5O12, then the mixture of powders (1e2% excess of Ga2O3) were pressed to sheet and sintered for 12 h at 1200e1400 C. Such formed materials were crushed, remixed and sintered again at 1200e1400 C for 24 h. Finally, we obtained polycrystalline materials. The crystal was grown by the Cz method in a iridium crucible with radio frequency (RF) induction heating. After that crystal growth was carried out under high purity N2 (99.99%) atmosphere. It was grown in the <111 > orientation at a pulling rate of 1.0 mm/h and a rotating rate of 10e15 rpm. Finally, Tb3-xTmxGa5O12 crystal was obtained. The transmission spectrum were measured using a PerkineElmer Lambda 900 UV-VIS-NIR spectrophotometer (United States) in transmission mode over the wavelength range of 300 nm2000 nm. The X-ray powder diffraction measurement was carried out by the Ultima IV (Rigaku, Japan). A schematic of the experimental is setup for investigating the Faraday effects. A light sources (Xe-lamp and monochromator) passed through the sample located between a pair of Glan laser prisms. The transmitted light power was measured using a power meter. A polarization plane of laser light was rotated by the Faraday effect because of the magnetic field. Commercial TGG crystal (CASTECH) utilized for the calibration. All the measurements were performed at room temperature.
(1)
where C0 is the initial solute concentration, and keff is effective segregation coefficient. In the Fig. 2, the cation distribution of Tm3þ ion as a function of the solid fraction is shown, as g increase, Tm3þ concentration in the crystal increases and Ga3þ concentration decreases, whereas Tb3þ concentration seems not to depend on the solid fraction. The distribution coefficient keff of Tm3þ is nearly 0.50. 3.2. Transmittance spectrum Fig. 3 shows the transmittance spectrum of Tm: TGG crystal. It is important for a good magneto-optical material to have a low absorption loss in some specific wavelength range, such as 532, 633 and 1064 nm. There are two absorption bands centered at around 660, 760 nm, which correspond to the transitions starting from the 3 H6 ground state of Tm3þ to higher levels 3F2,3, 3H4, respectively, while absorption band centered at 486 nm is mainly related to the energy level transition 7F6-5D4 of Tb3þ. It can be seen that Tm:TGG has good optical transparency which is around 80% in VIS-NIR. This parameter is very important for FIs applications, since the use of lengthy crystals requires minimizing optical losses. So the Tm:TGG crystal can be applied as a magneto-optical material in VIS-NIR FIs devices.
3. Results and discussion
3.3. Magnetic susceptibility
3.1. Structural analysis and phase stability
The magnetic susceptibility results of Tm:TGG are shown in Fig. 4. The c (T) decreases monotonously without any magnetic transition over the temperature range from 10 to 300 K under a constant magnetic field of 0.01 T. The inset of Fig. 4 indicates the reciprocal of c(T), which exhibits a linear dependence on T down to 10 K at least. The linear part of the reciprocal of c(T) can be described by the following Curie-Weiss equation which is defined as c ¼ C/(Teqp), where C is the Curie constant and qp is the Weiss temperature. The effective magnetic moment and CurieeWeiss
The Tb3-xTmxGa5O12 crystal which is shown in the insert of Fig. 1 was ground into powder and its X-ray powder diffraction pattern was shown in Fig. 1. Compared with the JCPDS standard card, the XRD powder diffraction pattern of doped crystal is agree well with the standard patterns of TGG crystal(JCPDS 88e0575) without any impurities peaks. The result indicates that the Tm3þ ion does not influence the crystal structure. The unitecell parameters were determined with the help of X Pert High Score Plus computer
Fig. 1. X-ray powder diffraction patterns of the Tm:TGG, Inset: Tm:TGG crystal was obtained by the Cz method.
Fig. 2. The Tm3þ distribution as a function of the solid fraction in the Tm:TGG crystal.
64
Z. Chen et al. / Journal of Alloys and Compounds 661 (2016) 62e65
Fig. 3. The transmission spectra of Tm:TGG crystal at measured wavelength.
Fig. 5. Faraday rotation of Tm:TGG crystal in different wavelengths at room temperature.
the magnetic susceptibility c as follows:
V¼
Fig. 4. The temperature dependence of the mass susceptibility of Tm:TGG crystal. Inset: inverse magnetic susceptibility versus temperature (H ¼ 0.01T).
temperature of Tm:TGG crystal are 9.78mB and 3.1K respectively. The temperature dependence of the magnetic susceptibility indicates that the Tm:TGG crystal exhibits paramagnetic behavior over the experimental temperature-range 10e300 K and the higher magnetic moment of Tb3þ ion may indicate that the magnetic ion in the Tm:TGG crystal are affected by the crystal field to some extent.
4p2 n2 c X Cij ij 2 gmB ch n nij2
(2)
Whereas n is the frequency of the incident light, nij is the transition frequency between electronic states, Cij is the transition factor, mB is the Bohr magneton, c is probability of this, g is the Lande the velocity of light, and h is the Planck constant. The experimental data are described by a single electronic transition, and the Verdet constant dispersion is given as a function E , whereas E of the wavelength l in simplified form as: V ¼ l2 l 2 0 includes all the constant terms, and l0 is the transition wavelength, which is associated with the electronic transition of paramagnetic RE ions. The results of the FR measurements are displayed in Fig. 6. The curves for Tm:TGG and TGG are very close to each other as the wavelength increased, while the values for Tm:TGG being much higher in the 400e1500 nm. It can be seen that Tm:TGG possesses a higher V value, with an increment of more than 20% independently of the considered wavelength in comparison with the reference TGG. The measured Verdet constants at wavelength of 532, 633, 830, 1064 and 1330 nm are 256.8, 178.6, 102.3, 60.2, 26.3 rad∕Tm, respectively, obviously larger than that of pure TGG. It can be
3.4. Magneto-optical characteristic For paramagnetic materials, the Faraday rotation qF is linear ratio to magnetic induction intensity B when the length of sample L is fixed. There exists a linear relationship between the Faraday rotation of Tm:TGG crystal and magnetic field in the range of 0e1.2 T at different wavelengths, as shown in Fig. 5. It could be concluded that Tm:TGG crystal belongs to pure paramagnetic substance at room temperature basing on the Faraday rotation dependence on an external magnetic field. The Faraday rotation of Tm:TGG crystal is close to 165 /cm in the 532 nm wavelength at 1.2T, almost 25% higher than that of TGG. This result confirm that the doping of Tm3þ ion significantly enhance the magneto-optical property in the garnet crystal. The FR of paramagnetic RE ions has been described by van Vleck-Hebb [17]. From quantum-mechanical considerations they deduced that the V constant dispersion is directly proportional to
Fig. 6. Verdet constant dispersion of Tm:TGG in comparison with that of TGG.
Z. Chen et al. / Journal of Alloys and Compounds 661 (2016) 62e65
65
7.0Wm1K1, dropping to nearly 4.2Wm1K1 at 500 C. The LIDT of measured was about 13.68J/cm2, shown in the Fig. 8. The LIDT value of Tm:TGG is almost same as the pure TGG. These results further confirm the high quality of the Tm:TGG crystal and its further application in the high power Faraday devices. 4. Conclusion
Fig. 7. The thermal conductivity of Tm:TGG compared with TGG crystal.
In conclusion, the presented results show the superior properties of Tm:TGG in comparison with TGG from any point of view related with FIs. Tm:TGG has more favorable growth characteristics and the increase of at least 20% in the Verdet constant is very significant, giving the huge possibility to reduce the intensity of the necessary magnetic fields, especially in the VIS-NIR. The Tm:TGG crystal exhibit paramagnetic behavior down to 10K. The measured thermal conductivity and LIDT features of Tm:TGG clearly indicate that this crystal is a promising magneto-optical material for highpower FIs applications. Tm:TGG has a high potential to substitute commercial TGG crystals used in FIs in the IR region (below 1100 nm) and more especially in the VIS. Acknowledgment This work was supported by Nature Science Foundation of China (Nos.51472257). References
Fig. 8. The laser induced damage threshold of the Tm:TGG at 1064 nm.
explained by that the magnetization depends on the splitting of the ground configuration induced by the spineorbit (SO) interaction, crystal field (CF), exchange interaction and external magnetic field. It should be emphasized that the exchange interaction between Tb3þ and Tm3þ ions, although much smaller, will have effects under some conditions in paramagnetic gallium garnet. 3.5. Thermal conductivity and LIDT measurement Since the thermal management is a very important point in high power laser system, thermal conductivity (Fig. 7) has been measured for Tm:TGG and TGG crystal. The curves of both are very close to each other, while the Tm:TGG being slightly lower in comparison with the reference TGG at the measured temperature. The thermal conductivity of Tm:TGG at room temperature was
[1] M.A. Kagan, E.A. Khazanov, Appl. Opt. 43 (2004) 6030. [2] R. Yasuhara, S. Tokita, J. Kawanaka, T. Kawashima, H. Kan, H. Yagi, H. Nozawa, T. Yanagitani, Y. Fujimoto, H. Yoshida, M. Nakatsuka, Opt. Express 15 (2007) 11255. [3] T. Nakanishi, M. Maeda, A. Kawashima, S. Kamiya, K. Fushimi, K. Fujita, K. Tanaka, Y. Hasegawa, J. Alloys Comp 562 (2013) 123. [4] R. Lisiecki, W. Ryba-Romanowski, P. Solarz, A. Strze˛p, M. Berkowski, J. Alloys Comp. 582 (2014) 208. [5] S. Banerjee, K. Ertel, P.D. Mason, P.J. Phillips, M. Siebold, et al., Opt. Lett. 37 (2012) 2175. [6] D. Zheleznov, A. Starobor, O. Palashov, C. Chen, S. Zhou, Opt. Express 22 (2014) 2578. [7] N. Rajamanickam, R.N. Mariammal, S. Rajashabala, K. Ramachandran, J. Alloy Compd. 614 (2014) 151. [8] Y.J. Wua, H.P. Fua, R.Y. Honga, Y. Zhengd, D.G. Weie, J. Alloy Compd. 470 (2009) 497. [9] G.J. Chen, H.M. Lee, Y.S. Chang, Y.J. Lin, Y.L. Chai, J. Alloys Compd. 388 (2005) 297. [10] A. Hasanpour, M. Mozaffari, J. Amighian, H. Richert, A. Lorenz, M. Lindner, P.G. Ornert, H. Heegn, J. Magn. Magn. Mater 317 (2007) 41. [11] J.J. Liu, F.Y. Guo, B. Zhao, N.F. Zhuang, Y.P. Chen, Z.P. Gao, J.Z. Chen, J. Cryst. Growth 310 (2008) 2613. [12] H.L. Zhu, D.L. Jin, L.M. Zhu, H. Yang, K.H. Yao, Z.Q. Xi, J. Alloy Compd. 464 (2008) 508. [13] V. Vasyliev, E.G. Villora, M. Nakamura, Y. Sugahara, K. Shimamura, Opt. Express 20 (2012) 14460. [14] D. Zheleznov, A. Starobor, O. Palashov, H. Lin, S. Zhou, Opt. Lett. 39 (2014) 2183. [15] C. Chen, S. Zhou, H. Lin, Q. Yi, Appl. Phys. Lett. 101 (2012) 131908. [16] K. Shimamura, T. Kito, E. Castel, et al., Cryst. Growth Des. 10 (2010) 3466. [17] V. Vasyliev, P. Molina, M. Nakamura, E.G. Víllora, K. Shimamura, Opt. Mater 33 (2011) 1710. [18] Z. Chen, Y. Hang, L. Yang, J. Wang, X.Y. Wang, et al., Opt. Lett. 40 (2015) 820. [19] Z. Chen, L. Yang, Y. Hang, J. Wang, X.Y. Wang, et al., Opt. Mater 47 (2015) 39. [20] Z. Chen, Y. Hang, L. Yang, J. Wang, X.Y. Wang, et al., Mater. Lett. 145 (2015) 171.