- Email: [email protected]
Irreversible magnetization in isovalently doped Ba(Fe1-xRux)2As2
Available online at www.sciencedirect.com
Physics Procedia 27 (2012) 104 – 107
ISS2011
Irreversible magnetization in isovalently doped Ba(Fe1-xRux)2As2 Tatsuro Ishibashia, Yasuyuki Nakajimaa,b, Tsuyoshi Tamegaia,b* a b
Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
JST, Transformative Research-Project on Iron Pnictides (TRIP), 7-3-1 Hongo, Bukyo-ku, Tokyo 113-8656, Japan
Abstract
We report the superconducting properties of single-crystalline Ba(Fe1-xRux)2As2 by measuring its resistivity, upper critical field, magnetization, and magneto-optical images. Ba(Fe1-xRux)2As2 single crystal shows superconductivity at ~ 20 K. The upper critical field determined by resistive transition is anisotropic with an anisotropy parameter of ~ 2.2. The irreversible magnetization measurement shows a diminished but distinct fish-tail effect and a relatively high critical current density over Jc = 6 × 105 A/cm2 at 2 K, slightly smaller than that in Co-doped BaFe2As2. © 2012 2011 Published Published by byElsevier ElsevierB.V. Ltd. Selection Selection and/or and/orpeer-review peer-reviewunder underresponsibility responsibilityofofISS ISSProgram ProgramCommittee Committee. © Keywords: Ba(Fe1-xRux)2As2, iron-pnictide; upper critical field; critical current density; magneto-optical imaging
1. Introduction Since the discovery of superconductivity in LaFeAs(O,F) [1], iron-based superconductors have attracted much interest because of their high critical temperatures and reasonable critical current densities. These materials share several commonalities with cuprates, with their layered structure comprised of a superconducting layer sandwiched by charge reservoir layers. Furthermore, the parent compounds are in most cases semi-metallic antiferromagnet, and a superconducting phase appears as the antiferromagnetic (AFM) phase is suppressed by external control parameters, such as doping or pressure. In iron-pnictides, superconductivity is induced either by charge doping or by isovalent substitutions. Known examples of the latter are the partial replacement of As by P [2,3], or Fe by Ru [4] in BaFe2As2 (122), while charge doping is achieved by replacing O by F in RFeAsO (1111) (R is a rare earth element) [1,5-8], and Ba by K, or Fe by transition metal ions in 122 [9,10]. Introduction of either type of substitution changes its band structure and substituted atoms act as scattering centers. One direct measurement of scattering in a superconductor is to monitor the degree of vortex pinning in these materials. Most of the studies on vortex physics in iron-based superconductors have focused on the K or Co doped 122 and some 1111 compounds [11-13]. It is important to mention that in these iron-based superconductors, irreversible magnetization show a fish-tail effect [10-14] similar to the cuprates. Recently, based on the measurements in isovalently doped BaFe2(As1-xPx)2, a model for the fish-tail effect is proposed that it is induced by the quasiparticle scattering due to the charged dopants [15]. In this paper, to verify this model for the origin of the fish-tail effect, we prepare single crystalline samples of another isovalently doped Ba(Fe1-xRux)2As2 and present their superconducting properties by studying its resistivity,
* Corresponding author. Tel.: +81-3-5841-6846 ; fax:+81-3-5841-8886 . E-mail address: [email protected] .
1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of ISS Program Committee doi:10.1016/j.phpro.2012.03.421
Tatsuro Ishibashi et al. / Physics Procedia 27 (2012) 104 – 107
105
upper critical field, magnetization, and magneto-optical images. We observed a diminished but distinct fish-tail effect in isovalently doped Ba(Fe1-xRux)2As2. 2. Experiments Single-crystalline samples of Ba(Fe1-xRux)2As2 with a compositionof x = 0.37 were grown by the FeAs/RuAs self-flux method [16-18]. FeAs and RuAs were prepared by placing mixtures of As pieces and Fe/Ru powder in a silica tube and reacting them at 1100͠ for 10 h after heating at 700͠ for 6 h. A mixture with a ratio of Ba : FeAs : RuAs = 1 : 4(1-x) : 4x was placed in an alumina crucible with quartz fibers as a cup. The whole assembly was sealed in a large silica tube, and heated up to 1150͠ for 10 h followed by slow cooling down to 800͠ at a rate of 1.5͠/h. The typical dimensions of the resulting crystals are 1 × 1 × 0.05 mm3. The average Ru concentration in the batch was determined by energy dispersive X-ray spectroscopy measurement. Magnetization was measured by a commercial SQUID magnetometer (Quantum Design MPMS-XL5). Resistivity measurement was performed by a four-probe method. Magneto-optical images were obtained using the local-field-dependent Faraday effect with an in-plane magnetized garnet indicator film and employing a differential method [1920] . 3. Results and discussion Figure 1(a) shows the temperature dependence of in-plane resistivity in Ba(Fe0.63Ru0.37)2As2. With decreasing temperature from 300 K, resistivity decreases linearly and then starts to drop at Tc ~ 22 K. There is no anomaly accompanied by a structural/magnetic transition reported in the parent material BaFe2As2 [21], which indicates that the transition is suppressed by Ru doping. The residual resistivity ratio ȡ(300 K)/ȡ(Tc) is ~ 4.1, which is comparable to that reported before [16-18]. Figures 1(b), (c) show low-temperature in-plane resistivity data at H = 0, 10, 20, 30, 40, and 50 kOe along the ab-plane and c-axis respectively. With increasing field, Tc decreases and transition width is broadened only slightly. We plot the upper critical field Hc2 along the ab- and c-directions determined by the midpoint of resistive transition as a function of temperature in Fig. 1(d). The slopes of Hc2 along the ab- and c-directions at Tc are -33.1 and -15.3 kOe/K, respectively. From the Werthamer-Helfand-Hohenberg theory [22], which describes orbital depairing field of conventional dirty type-II superconductors, we can obtain the values of Hc2(0) = 0.69Tc|dHc2/dT|T = Tc ~ 480 and 220 kOe along the ab- and c-directions, respectively. The anisotropy of the upper critical field Ȗ ҂ Hc2ab/Hc2c is ~ 2.2. This value is similar to that of other Ba122 systems [10,23,24].
Fig. 1. (a) temperature dependence of zero-field resistivity in Ba(Fe0.63Ru0.37)2As2. (b),(c) in-plane resistivity as a function of temperature near Tc at H = 0 , 10, 20, 30, 40, and 50 kOe along ab- and c-directions, respectively. (d) Temperature dependence of upper critical field along ab-plane and caxis defined by the midpoint of resistive transition in Ba(Fe0.63Ru0.37)2As. Solid lines are linear fits to the data.
106
Tatsuro Ishibashi et al. / Physics Procedia 27 (2012) 104 – 107
Figure 2 shows the temperature dependence of zero-field-cooled (ZFC) and field-cooled (FC) magnetizations at 5 Oe along c-axis. A sharp transition starting from Tc ~ 20 K is observed. Figure 3(a) shows the irreversible magnetization at several temperatures as a function of field. A diminished but distinct fish-tail effect is observed, which is very similar to that in cuprates [25] and other charge doped 122 and 1111 compounds [10-13]. Recently Fishtail effect is also observed in isovalently doped BaFe2(As1-xPx)2 [26], FeTe1-xSex [14] and LiFeAs without charge doping [27]. These results do not support the recently proposed model accounting for fish-tail effect.
Fig. 2. Temperature dependence of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization at H = 5 Oe along c-axis in Ba(Fe0.63Ru0.37)2As2
Fig. 3. (a) Field dependence of irreversible magnetization along c-axis in Ba(Fe0.63Ru0.37)2As2 at 2, 5, 10, and 15 K. (b) Field dependence of critical current density obtained from the data shown in (a) in Ba(Fe0.63Ru0.37)2As2 at 2, 5, 10, and 15 K.
From the irreversible magnetization, we can obtain the critical current density Jc using the Bean model with the assumption of field-independent Jc. According to the Bean model, Jc is given by [28] Jc
20 ' M a (1 a / 3b ) ,
(1) where ǻM [emu/cc] is Mdown -Mup, Mup and Mdown are the magnetization when sweeping fields up and down, respectively, and a [cm] and b [cm] are the sample widths with a < b. Fig. 3(b) shows the field dependence of Jc [A/cm2] obtained from the data shown in Fig. 3(a) using eq. (1) and the effective sample dimensions with a ~ 410 ȝm and b ~ 840 ȝm. Jc reaches to 6 × 105A/cm2 at 2 K. This value is comparable but a little smaller than other 122 systems [10,11].
Fig. 4. (a) A magneto-optical image in the remanent state after applying H = 800 Oe in Ba(Fe0.63Ru0.37)2As2 at 5 K. (b) The profile of magnetic induction along the line AB shown in (a).
Tatsuro Ishibashi et al. / Physics Procedia 27 (2012) 104 – 107
107
Figure 4(a) shows a magneto-optical image of Ba(Fe0.63Ru0.37)2As2 in the remanent state at 5 K. This state is made by applying 800 Oe along c-axis for 1 s and removing it after zero-field cooling. The bright region in Fig. 4(a) corresponds to the area trapping vortices. Figure 4(b) shows the profile of magnetic induction along line AB in Fig. 4(a). From Fig. 4(b), we can roughly estimate the critical current Jc ~ ǻB/t, where ǻB is the trapped field and t is the thickness of the sample. With 'B ~ 416 G and t ~ 15 ȝm, Jc is estimated as ~ 2.8 × 105 A/cm2 at 5 K. This value compares well with the value calculated from irreversible magnetization ~ 4.7 × 105 A/cm2. 4. Summary We have performed a systematic studies of resistivity, upper critical field, magnetization, and magneto-optical imaging of single-crystalline Ba(Fe1-xRux)2As2. The upper critical field obtained by resistive transition is anisotropic with an anisotropy parameter of 2.2. The magneto-optical imaging reveals prominent Bean-like penetrations of vortices although there is slight inhomogeneities in the sample, with Jc ~ 3 × 105 A/cm2 at 5 K. We also observed a diminished but distinct fish-tail effect in isovalently doped Ba(Fe1-xRux)2As2. References [1] Y. Kamihara, T. Watanabe, M. Hirano, H. Hosono, J. Am. Chem. Soc. 130 (2008) 3296. [2] S. Jiang, H. Xing, G. Xuan, C. Wang, Z. Ren, C. Feng et al., J. Phys. Condens. Matter 21 (2009) 382203. [3] H. Shishido, A. F. Bangura, A. I. Coldea, S. Tonegawa, K. Hashimoto, S. Kasahara et al., Phys. Rev. Lett. 104 (2010) 057008. [4] S. Sharma, A. Bharathi, S. Chandra, V. Raghavendra Reddy, S Paulraj, A. T. Satya et al., Phys. Rev. B 81 (2010) 174512. [5] H. Takahashi, K. Igawa, K. Arii, Y. Kamihara, M. Hirano, and H. Hosono, Nature 453 (2008) 376. [6] G. F. Chen, Z. Li, D. Wu, G. Li, W. Z. Hu, J. Dong et al., Phys. Rev. Lett. 100 (2008) 247002. [7]Z. A. Ren, J. Yang, W. Lu, W. Yi, G. C. Che, X. L. Dong et al., Mater. Res. Innovations. 12 (2008) 105. [8] H. Kito, H. Eisaki, and A. Iyo, J. Phys. Soc. Jpn. 77 (2008) 063707. [9] M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. 101 (2008) 107006. [10] Y. Nakajima, T. Taen, and T. Tamegai, J. Phys. Soc. Jpn. 78 (2009) 023702. [11] R. Prozorov, N. Ni, M. Tanatar, V. Kogan, R. Gordon, C. Martin et al., Phys. Rev. B 78 (2008) 224506. [12] H. Yang, H. Luo, Z. Wang, and H. H. Wen, Appl. Phys. Lett. 93 (2008) 142506. [13] C. J. van der Beek, G. Rizza, M. Konczykowski, P. Fertey, I. Monnet, T. Klein, et al., Phys. Rev. B 81 (2010) 174517. [14] T. Taen, Y. Tsuchiya, Y. Nakajima, and T. Tamegai, Phys. Rev. B 81 (2009) 092502. [15] C. J. van der Beek, M. Konczykowski, S. Kasahara, T. Terashima, R. Okazaki, T. Shibauchi, and Y. Matsuda, Phys. Rev. Lett. 105 (2010) 267002. [16] A. Thaler, N. Ni, A. Kracher, J. Yan, S. Bud’ko, and P. C. Canfield, Phys. Rev. B 82 (2010) 014534. [17] F. Rullier-Albenque, D. Colson, A. Forget, P. Thuéry, and S. Poissonnet, Phys. Rev. B 81 (2010) 224503. [18] M. J. Eom, S. W. Na, C. Hoch, R. K. Kremer, and J. S. Kim, arXiv:1109.1083. [19] A. Soibel, E. Zeldov, M. Rappaport, Y. Myasoedov, T. Tamegai, S. Ooi et al., Nature 406 (2000) 282. [20] M. Yasugaki, K. Itaka, M. Tokunaga, M. Kameda, and T. Tamegai, Phys. Rev. B 65 (2002) 212502. [21] M. Rotter, M. Tegel, D. Johrendt, I. Schellenberg, W. Hermes, and R. Pottgen, Phys. Rev. B 78 (2008) 020503R. [22] N. R. Werthamer, E. Helfand, and P. C. Hohenberg, Phys. Rev. 147 (1966) 295. [23] N. Ni, S. L. Bud’ko, A. Kreyssig, S. Nandi, G. E. Rustan, A. I. Goldman et al., Phys. Rev. B 78 (2008) 014507. [24] A. Yamamoto, J. Jaroszynski, C. Tarantini, L. Balicas, J. Jiang, A. Gurevich et al., Appl. Phys. Lett. 94 (2009) 062511. [25] M. Däumling, J. M. Seuntjens, and D. C. Larbalestier, Nature 346 (1990) 332. [26] L. Fang, Y. Jia, J. Schlueter, A. Kayani, Z. Xiao, H. Claus et al., Phys. Rev. B 84 (2011) 140504. [27] A. Pramanik, L. Harnagea, C. Nacke, A. Wolter, S. Wurmehl, V. Kataev, and B. Büchner, Phys. Rev. B 83 (2011) 094502. [28] C. P. Bean, Rev. Mod. Phys. 36 (1964) 31.
Physics Procedia 27 (2012) 104 – 107
ISS2011
Irreversible magnetization in isovalently doped Ba(Fe1-xRux)2As2 Tatsuro Ishibashia, Yasuyuki Nakajimaa,b, Tsuyoshi Tamegaia,b* a b
Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
JST, Transformative Research-Project on Iron Pnictides (TRIP), 7-3-1 Hongo, Bukyo-ku, Tokyo 113-8656, Japan
Abstract
We report the superconducting properties of single-crystalline Ba(Fe1-xRux)2As2 by measuring its resistivity, upper critical field, magnetization, and magneto-optical images. Ba(Fe1-xRux)2As2 single crystal shows superconductivity at ~ 20 K. The upper critical field determined by resistive transition is anisotropic with an anisotropy parameter of ~ 2.2. The irreversible magnetization measurement shows a diminished but distinct fish-tail effect and a relatively high critical current density over Jc = 6 × 105 A/cm2 at 2 K, slightly smaller than that in Co-doped BaFe2As2. © 2012 2011 Published Published by byElsevier ElsevierB.V. Ltd. Selection Selection and/or and/orpeer-review peer-reviewunder underresponsibility responsibilityofofISS ISSProgram ProgramCommittee Committee. © Keywords: Ba(Fe1-xRux)2As2, iron-pnictide; upper critical field; critical current density; magneto-optical imaging
1. Introduction Since the discovery of superconductivity in LaFeAs(O,F) [1], iron-based superconductors have attracted much interest because of their high critical temperatures and reasonable critical current densities. These materials share several commonalities with cuprates, with their layered structure comprised of a superconducting layer sandwiched by charge reservoir layers. Furthermore, the parent compounds are in most cases semi-metallic antiferromagnet, and a superconducting phase appears as the antiferromagnetic (AFM) phase is suppressed by external control parameters, such as doping or pressure. In iron-pnictides, superconductivity is induced either by charge doping or by isovalent substitutions. Known examples of the latter are the partial replacement of As by P [2,3], or Fe by Ru [4] in BaFe2As2 (122), while charge doping is achieved by replacing O by F in RFeAsO (1111) (R is a rare earth element) [1,5-8], and Ba by K, or Fe by transition metal ions in 122 [9,10]. Introduction of either type of substitution changes its band structure and substituted atoms act as scattering centers. One direct measurement of scattering in a superconductor is to monitor the degree of vortex pinning in these materials. Most of the studies on vortex physics in iron-based superconductors have focused on the K or Co doped 122 and some 1111 compounds [11-13]. It is important to mention that in these iron-based superconductors, irreversible magnetization show a fish-tail effect [10-14] similar to the cuprates. Recently, based on the measurements in isovalently doped BaFe2(As1-xPx)2, a model for the fish-tail effect is proposed that it is induced by the quasiparticle scattering due to the charged dopants [15]. In this paper, to verify this model for the origin of the fish-tail effect, we prepare single crystalline samples of another isovalently doped Ba(Fe1-xRux)2As2 and present their superconducting properties by studying its resistivity,
* Corresponding author. Tel.: +81-3-5841-6846 ; fax:+81-3-5841-8886 . E-mail address: [email protected] .
1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of ISS Program Committee doi:10.1016/j.phpro.2012.03.421
Tatsuro Ishibashi et al. / Physics Procedia 27 (2012) 104 – 107
105
upper critical field, magnetization, and magneto-optical images. We observed a diminished but distinct fish-tail effect in isovalently doped Ba(Fe1-xRux)2As2. 2. Experiments Single-crystalline samples of Ba(Fe1-xRux)2As2 with a compositionof x = 0.37 were grown by the FeAs/RuAs self-flux method [16-18]. FeAs and RuAs were prepared by placing mixtures of As pieces and Fe/Ru powder in a silica tube and reacting them at 1100͠ for 10 h after heating at 700͠ for 6 h. A mixture with a ratio of Ba : FeAs : RuAs = 1 : 4(1-x) : 4x was placed in an alumina crucible with quartz fibers as a cup. The whole assembly was sealed in a large silica tube, and heated up to 1150͠ for 10 h followed by slow cooling down to 800͠ at a rate of 1.5͠/h. The typical dimensions of the resulting crystals are 1 × 1 × 0.05 mm3. The average Ru concentration in the batch was determined by energy dispersive X-ray spectroscopy measurement. Magnetization was measured by a commercial SQUID magnetometer (Quantum Design MPMS-XL5). Resistivity measurement was performed by a four-probe method. Magneto-optical images were obtained using the local-field-dependent Faraday effect with an in-plane magnetized garnet indicator film and employing a differential method [1920] . 3. Results and discussion Figure 1(a) shows the temperature dependence of in-plane resistivity in Ba(Fe0.63Ru0.37)2As2. With decreasing temperature from 300 K, resistivity decreases linearly and then starts to drop at Tc ~ 22 K. There is no anomaly accompanied by a structural/magnetic transition reported in the parent material BaFe2As2 [21], which indicates that the transition is suppressed by Ru doping. The residual resistivity ratio ȡ(300 K)/ȡ(Tc) is ~ 4.1, which is comparable to that reported before [16-18]. Figures 1(b), (c) show low-temperature in-plane resistivity data at H = 0, 10, 20, 30, 40, and 50 kOe along the ab-plane and c-axis respectively. With increasing field, Tc decreases and transition width is broadened only slightly. We plot the upper critical field Hc2 along the ab- and c-directions determined by the midpoint of resistive transition as a function of temperature in Fig. 1(d). The slopes of Hc2 along the ab- and c-directions at Tc are -33.1 and -15.3 kOe/K, respectively. From the Werthamer-Helfand-Hohenberg theory [22], which describes orbital depairing field of conventional dirty type-II superconductors, we can obtain the values of Hc2(0) = 0.69Tc|dHc2/dT|T = Tc ~ 480 and 220 kOe along the ab- and c-directions, respectively. The anisotropy of the upper critical field Ȗ ҂ Hc2ab/Hc2c is ~ 2.2. This value is similar to that of other Ba122 systems [10,23,24].
Fig. 1. (a) temperature dependence of zero-field resistivity in Ba(Fe0.63Ru0.37)2As2. (b),(c) in-plane resistivity as a function of temperature near Tc at H = 0 , 10, 20, 30, 40, and 50 kOe along ab- and c-directions, respectively. (d) Temperature dependence of upper critical field along ab-plane and caxis defined by the midpoint of resistive transition in Ba(Fe0.63Ru0.37)2As. Solid lines are linear fits to the data.
106
Tatsuro Ishibashi et al. / Physics Procedia 27 (2012) 104 – 107
Figure 2 shows the temperature dependence of zero-field-cooled (ZFC) and field-cooled (FC) magnetizations at 5 Oe along c-axis. A sharp transition starting from Tc ~ 20 K is observed. Figure 3(a) shows the irreversible magnetization at several temperatures as a function of field. A diminished but distinct fish-tail effect is observed, which is very similar to that in cuprates [25] and other charge doped 122 and 1111 compounds [10-13]. Recently Fishtail effect is also observed in isovalently doped BaFe2(As1-xPx)2 [26], FeTe1-xSex [14] and LiFeAs without charge doping [27]. These results do not support the recently proposed model accounting for fish-tail effect.
Fig. 2. Temperature dependence of the zero-field-cooled (ZFC) and field-cooled (FC) magnetization at H = 5 Oe along c-axis in Ba(Fe0.63Ru0.37)2As2
Fig. 3. (a) Field dependence of irreversible magnetization along c-axis in Ba(Fe0.63Ru0.37)2As2 at 2, 5, 10, and 15 K. (b) Field dependence of critical current density obtained from the data shown in (a) in Ba(Fe0.63Ru0.37)2As2 at 2, 5, 10, and 15 K.
From the irreversible magnetization, we can obtain the critical current density Jc using the Bean model with the assumption of field-independent Jc. According to the Bean model, Jc is given by [28] Jc
20 ' M a (1 a / 3b ) ,
(1) where ǻM [emu/cc] is Mdown -Mup, Mup and Mdown are the magnetization when sweeping fields up and down, respectively, and a [cm] and b [cm] are the sample widths with a < b. Fig. 3(b) shows the field dependence of Jc [A/cm2] obtained from the data shown in Fig. 3(a) using eq. (1) and the effective sample dimensions with a ~ 410 ȝm and b ~ 840 ȝm. Jc reaches to 6 × 105A/cm2 at 2 K. This value is comparable but a little smaller than other 122 systems [10,11].
Fig. 4. (a) A magneto-optical image in the remanent state after applying H = 800 Oe in Ba(Fe0.63Ru0.37)2As2 at 5 K. (b) The profile of magnetic induction along the line AB shown in (a).
Tatsuro Ishibashi et al. / Physics Procedia 27 (2012) 104 – 107
107
Figure 4(a) shows a magneto-optical image of Ba(Fe0.63Ru0.37)2As2 in the remanent state at 5 K. This state is made by applying 800 Oe along c-axis for 1 s and removing it after zero-field cooling. The bright region in Fig. 4(a) corresponds to the area trapping vortices. Figure 4(b) shows the profile of magnetic induction along line AB in Fig. 4(a). From Fig. 4(b), we can roughly estimate the critical current Jc ~ ǻB/t, where ǻB is the trapped field and t is the thickness of the sample. With 'B ~ 416 G and t ~ 15 ȝm, Jc is estimated as ~ 2.8 × 105 A/cm2 at 5 K. This value compares well with the value calculated from irreversible magnetization ~ 4.7 × 105 A/cm2. 4. Summary We have performed a systematic studies of resistivity, upper critical field, magnetization, and magneto-optical imaging of single-crystalline Ba(Fe1-xRux)2As2. The upper critical field obtained by resistive transition is anisotropic with an anisotropy parameter of 2.2. The magneto-optical imaging reveals prominent Bean-like penetrations of vortices although there is slight inhomogeneities in the sample, with Jc ~ 3 × 105 A/cm2 at 5 K. We also observed a diminished but distinct fish-tail effect in isovalently doped Ba(Fe1-xRux)2As2. References [1] Y. Kamihara, T. Watanabe, M. Hirano, H. Hosono, J. Am. Chem. Soc. 130 (2008) 3296. [2] S. Jiang, H. Xing, G. Xuan, C. Wang, Z. Ren, C. Feng et al., J. Phys. Condens. Matter 21 (2009) 382203. [3] H. Shishido, A. F. Bangura, A. I. Coldea, S. Tonegawa, K. Hashimoto, S. Kasahara et al., Phys. Rev. Lett. 104 (2010) 057008. [4] S. Sharma, A. Bharathi, S. Chandra, V. Raghavendra Reddy, S Paulraj, A. T. Satya et al., Phys. Rev. B 81 (2010) 174512. [5] H. Takahashi, K. Igawa, K. Arii, Y. Kamihara, M. Hirano, and H. Hosono, Nature 453 (2008) 376. [6] G. F. Chen, Z. Li, D. Wu, G. Li, W. Z. Hu, J. Dong et al., Phys. Rev. Lett. 100 (2008) 247002. [7]Z. A. Ren, J. Yang, W. Lu, W. Yi, G. C. Che, X. L. Dong et al., Mater. Res. Innovations. 12 (2008) 105. [8] H. Kito, H. Eisaki, and A. Iyo, J. Phys. Soc. Jpn. 77 (2008) 063707. [9] M. Rotter, M. Tegel, and D. Johrendt, Phys. Rev. Lett. 101 (2008) 107006. [10] Y. Nakajima, T. Taen, and T. Tamegai, J. Phys. Soc. Jpn. 78 (2009) 023702. [11] R. Prozorov, N. Ni, M. Tanatar, V. Kogan, R. Gordon, C. Martin et al., Phys. Rev. B 78 (2008) 224506. [12] H. Yang, H. Luo, Z. Wang, and H. H. Wen, Appl. Phys. Lett. 93 (2008) 142506. [13] C. J. van der Beek, G. Rizza, M. Konczykowski, P. Fertey, I. Monnet, T. Klein, et al., Phys. Rev. B 81 (2010) 174517. [14] T. Taen, Y. Tsuchiya, Y. Nakajima, and T. Tamegai, Phys. Rev. B 81 (2009) 092502. [15] C. J. van der Beek, M. Konczykowski, S. Kasahara, T. Terashima, R. Okazaki, T. Shibauchi, and Y. Matsuda, Phys. Rev. Lett. 105 (2010) 267002. [16] A. Thaler, N. Ni, A. Kracher, J. Yan, S. Bud’ko, and P. C. Canfield, Phys. Rev. B 82 (2010) 014534. [17] F. Rullier-Albenque, D. Colson, A. Forget, P. Thuéry, and S. Poissonnet, Phys. Rev. B 81 (2010) 224503. [18] M. J. Eom, S. W. Na, C. Hoch, R. K. Kremer, and J. S. Kim, arXiv:1109.1083. [19] A. Soibel, E. Zeldov, M. Rappaport, Y. Myasoedov, T. Tamegai, S. Ooi et al., Nature 406 (2000) 282. [20] M. Yasugaki, K. Itaka, M. Tokunaga, M. Kameda, and T. Tamegai, Phys. Rev. B 65 (2002) 212502. [21] M. Rotter, M. Tegel, D. Johrendt, I. Schellenberg, W. Hermes, and R. Pottgen, Phys. Rev. B 78 (2008) 020503R. [22] N. R. Werthamer, E. Helfand, and P. C. Hohenberg, Phys. Rev. 147 (1966) 295. [23] N. Ni, S. L. Bud’ko, A. Kreyssig, S. Nandi, G. E. Rustan, A. I. Goldman et al., Phys. Rev. B 78 (2008) 014507. [24] A. Yamamoto, J. Jaroszynski, C. Tarantini, L. Balicas, J. Jiang, A. Gurevich et al., Appl. Phys. Lett. 94 (2009) 062511. [25] M. Däumling, J. M. Seuntjens, and D. C. Larbalestier, Nature 346 (1990) 332. [26] L. Fang, Y. Jia, J. Schlueter, A. Kayani, Z. Xiao, H. Claus et al., Phys. Rev. B 84 (2011) 140504. [27] A. Pramanik, L. Harnagea, C. Nacke, A. Wolter, S. Wurmehl, V. Kataev, and B. Büchner, Phys. Rev. B 83 (2011) 094502. [28] C. P. Bean, Rev. Mod. Phys. 36 (1964) 31.