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Coexistence of superconductivity and magnetism in the La0.87−xLnxSr0.13FeAsO (Ln=Sm, Gd, Dy) system
Journal of Physics and Chemistry of Solids 72 (2011) 442–444
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Coexistence of superconductivity and magnetism in the La0.87 xLnxSr0.13FeAsO (Ln ¼ Sm, Gd, Dy) system T.P. Lu, C.C. Wu, W.H. Chou, M.D. Lan n Department of Physics, National Chung Hsing University, Taiwan, ROC
a r t i c l e in f o
a b s t r a c t
Available online 7 October 2010
The interplay between the superconducting phase and spin density wave order phase was studied. We report the magnetic and superconducting properties of the hole-doped FeAs-based superconducting compound La0.87 xLnxSr0.13FeAsO (Ln ¼ Sm, Gd, Dy; 0 r x r 0.06). Both resistivity and magnetic susceptibility measurements show that the superconducting transition temperature decreases with increase in composition of magnetic ions. The hysteresis loop of the La0.87 xLnxSr0.13FeAsO sample shows a superconducting hysteresis in addition to a paramagnetic background. The experiment demonstrates that the magnetism and superconductivity coexist in hole-doped FeAs-based superconducting compounds. Among these three magnetic rare-earth elements, the influence of Dy3 + doping on superconductivity is more evident than that of Gd3 + doping, while the influence of Sm3 + doping is the weakest. The trend is consistent with the variation of the lattice parameter along c-axis. & 2010 Elsevier Ltd. All rights reserved.
Keywords: A. Hole-doped superconductor A. Iron-based superconductor D. Paramagnetic D. Spin density wave
1. Introduction The recently discovered superconductivity in the iron-based layered compound LaFeAsO stimulates intensive studies in both fundamental research and potential application [1]. The superconducting transition temperature was raised to 55 K [2–5] shortly after substituting lanthanum with a number of other rareearth elements. So far most of the discovered superconductors are categorized into the so-called electron doped type. Wen et al. [6,] and Mu et al. [7] found that by partially substituting Sr2 + for La3 + in LaFeAsO, the resultant material La1 xSrxFeAsO became the first hole-doped superconductor in iron-based systems, but the highest transition temperature found is only 25 K. The presence of Fermi surface nesting may lead to SDW instability around 150 K and suppress the superconductivity. In an electron-doped superconductor of iron-based systems, the replacement of lanthanum by magnetic ions leads to deviation of the lattice parameter along c-axis further from the LaFeAsO phase and enhances the superconductivity. This is really surprising since rare-earth elements generally give rise to magnetic moments, and destroy the superconductivity. In the hole-doped superconducting system La1 xSrxFeAsO, the superconductivity is degraded by the substitution of La with Sm in the paper that we presented previously [8]. The result is completely different from that of the electron-doped system. In this paper, we substitute lanthanum with a number of other rare-earth elements to understand the
role of magnetic ions on the superconductivity in the hole-doped FeAs-based superconducting compounds.
2. Sample preparation and experiment A series of polycrystalline samples (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) were fabricated by the conventional solid state reaction method. The synthesis process includes two steps. First, La1 yLnyAs was prepared by reacting grains of La (purity 99.99%), Gd (purity 99.95%), Dy (purity 99.95%), Sm (purity 99.95%), and As grains (purity 99.999%) at 900 1C for 12 h, and then at 1180 1C for 40 h. They were sealed in an evacuated quartz tube during the reaction. The resultant pellet was then smashed and ground together with the FeAs power, SrO powder (purity 99.9%), Fe powder (purity 99.95%), and Fe2O3 powder (purity 99.5%) in stoichiometry as the formula (La0.87 xLnxSr0.13)FeAsO. Again, it was pressed into a pellet, sealed in an evacuated quartz tube, and burned at about 940 1C for 4 h, followed by burning at 1150–1200 1C for 48 h. It was finally cooled down slowly to room temperature. The quality and structure of the specimen were characterized by a Siemens D5000 power X-ray diffractometer using CuKa radiation at room temperature. The low field dc magnetic response and magnetic hysteresis loop were measured by a Quantum Design SQUID magnetometer.
3. Results and discussion n
Corresponding author. Tel.: + 886 4 22840427x396; fax: + 886 4 22850458. E-mail address: [email protected] (M.D. Lan).
0022-3697/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2010.10.013
In Fig. 1, we summarized the lattice constants along c-axis for all samples. The lattice parameters were determined by the
T.P. Lu et al. / Journal of Physics and Chemistry of Solids 72 (2011) 442–444
Fig. 1. Doping dependence of lattice constants along c-axis. The influence of Dy3 + doping is more evident than that of Gd3 + , while the influence of Sm3 + is the weakest among these three rare-earth elements.
443
method of least squares fit using 8 reflections in the powder X-ray diffraction patterns. The lattice constant along c-axis shrinks in comparison with the value of the (La0.87Sr0.13)FeAsO phase. But the lattice parameters along c-axis approach the value of the parent LaFeAsO phase, which is not superconducting. In addition, the influence of Dy3 + doping on the structure is more evident than that of Gd3 + doping, while the influence of Sm3 + doping is the weakest among these three rare-earth elements. This is reasonable since the radii of Sm3 + , Gd3 + , and Dy3 + are about 1.13, ˚ respectively, which are slightly smaller than that 1.11, and 1.07 A, ˚ of La3 + of about 1.15 A. In Fig. 2, we show the temperature dependence of resistivity for (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) samples. The superconducting transition temperature Tc decreases with increase in x for rare-earth element substitutions in the low temperature region. The inset shows the temperature dependence of dr/dT, it shows that Tc decreases with increase in x for rareearth element substitutions more clearly. In addition, with the same ratio of substitutions, we observed the influence of Dy3 + doping on Tc decreases is more evident than that by Gd3 + , while the influence of Sm3 + is the weakest. This doping dependence of Tc is quite similar to that in c-axis lattice constants. The influence of Tc and the structure of doping Dy3 + is more evident than others.
Fig. 2. Temperature dependence of dr/dT for (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) samples. Inset shows the temperature dependence of resistivity.
Fig. 3. Temperature dependence of magnetization measured for (La0.87 xLnxSr0.13) FeAsO (Ln¼Sm, Gd, Dy) samples under a 5 Oe applied field.
Fig. 4. (a) Magnetization hysteresis loops of La0.87 xGdxSr0.13FeAsO (x¼ 0, 0.04, and 0.06) samples measured at 5 K. Inset shows the enlarged view of initial magnetization in the low field region. (b) Magnetization hysteresis loops of La0.87 xDyxSr0.13FeAsO (x¼ 0, 0.04, and 0.06) samples measured at 5 K. Inset shows the enlarged view of initial magnetization in the low field region.
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T.P. Lu et al. / Journal of Physics and Chemistry of Solids 72 (2011) 442–444
This indicates that decrease in Tc is due to the shortness of the lattice constant along c-axis in the hole-doped system. Typical low-field magnetization responses for (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) samples under a 5 Oe applied field is shown in Fig. 3. In general, the superconducting transition temperature Tc decreases with increase in x for rare-earth element substitutions. The influence of Sm3+ doping is the weakest among these three magnetic rare-earth elements. We observed the onset of the superconducting transition temperature Tc in the La0.81Sm0.06Sr0.13FeAsO compound is higher than that in the La0.83Gd0.04Sr0.13FeAsO and La0.83Dy0.04 Sr0.13FeAsO compounds. The diamagnetic signal decreases with the composition of the rare-earth substitutions. The substitution of Dy3 + for La3+ is more efficient in destroying Tc. The transition temperature Tc determined from the magnetic response measurement is slightly lower than that determined from the resistivity measurement. Both trends of reducing Tc are consistent with the variation of lattice parameters, in particular, along the c-axis. Fig. 4(a) and (b) shows the magnetic hysteresis loops of (La0.87 xGdxSr0.13)FeAsO and (La0.87 xGdxSr0.13)FeAsO (x¼0, 0.04, and 0.06) samples at 5 K. The size of the superconducting loop in the (La0.87 xLnxSr0.13)FeAsO system is shrank with increase in x. The impressed feature shown in the figure is that the superconducting hysteresis loop of the La1 xSrxFeAsO compound is superimposed on the paramagnetic background. The paramagnetic signal increases with increase in concentration of rare-earth magnetic ions, but it is not significant for the La1 xSrxFeAsO compound. The result implies superconductivity can coexist with a small but non-negligible magnetic moment in hole-doped FeAs-based superconductors.
4. Conclusion In both electron-type and hole-type FeAs-based superconducting compounds, magnetism and superconductivity can coexist. The superconductivity is suppressed by increasing rare-earth
element substitutions in the hole-doped systems, which is quite different from the electron-doped systems. Besides, the influence of Dy3 + doping on superconductivity is more evident than that of Gd3 + doping, while the influence of Sm3 + doping is the weakest. The trend is consistent with the variation of the lattice parameter along c-axis. Meanwhile doping rare-earth elements in FeAs-based superconductors would lead to a change of the lattice parameter along c-axis. This could be the main reason for causing the reduction of Tc. The occurrence of spin-density-wave instability may play a more dominant role in the suppression of superconductivity in the hole-doped FeAs-based superconductor.
Acknowledgement This work was supported by the National Science Council of the Republic of China under Contract no. NSC 98-2112-M-005-007. References [1] Kamihara Yoichi, Watanabe Takumi, Hirano Masahiro, Hosono Hideo, J. Am. Chem. Soc. 130 (2008) 3296. [2] Zhi-An Ren, Wei Lu, Jie Yang, Wei Yi, Xiao-Li Shen, Zheng-Cai, Guang-Can Che, Xiao-Li Dong, Li-Ling Sun, Fang Zhou, Zhong-Xian Zhao, Chin. Phys. Lett. 25 (2008) 2215. [3] Peng Cheng, Lei Fang, Huan Yang, Xiyu Zhu, Gang Mu, Huiqian Luo, Zhaosheng Wang, Hai-Hu Wen, Sci. Chin. Phys. Mech. Astron. 51 (2008) 719. [4] Athena S. Sefat, Ashfia Huq, Michael A. McGuire, Rongying Jin, Brian C. Sales, David Mandrus, M.D.Cranswick Lachlan, W.Stephens Peter, H.Stone Kevin, Phys. Rev. B 78 (2008) 104505. [5] Guang-Can Zhi-An Ren, Xiao-Li Che, Jie Dong, Wei Yang, Wei Lu, Xiao-Li Yi, Zheng-Cai Shen, Li-Ling Li, Fang Sun, Zhong-Xian Zhao. Zhou, Europhys. Lett. 83 (2008) 17002. [6] Hai-Hu Wen, Gang Mu, Lei Fang, Huan Yang, Xiyu Zhu, Europhys. Lett. 82 (2008) 17009. [7] Gang Mu, Lei Fang, Huan Yang, Xiyu Zhu, Peng Cheng, Hai-Hu Wen, J. Phys. Soc. Jpn. 77 (2008) 15. [8] T.P. Lu, C.C. Wu, W.H. Chou, M.D. Lan, Physica C 470 (2010) 357–359.
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Coexistence of superconductivity and magnetism in the La0.87 xLnxSr0.13FeAsO (Ln ¼ Sm, Gd, Dy) system T.P. Lu, C.C. Wu, W.H. Chou, M.D. Lan n Department of Physics, National Chung Hsing University, Taiwan, ROC
a r t i c l e in f o
a b s t r a c t
Available online 7 October 2010
The interplay between the superconducting phase and spin density wave order phase was studied. We report the magnetic and superconducting properties of the hole-doped FeAs-based superconducting compound La0.87 xLnxSr0.13FeAsO (Ln ¼ Sm, Gd, Dy; 0 r x r 0.06). Both resistivity and magnetic susceptibility measurements show that the superconducting transition temperature decreases with increase in composition of magnetic ions. The hysteresis loop of the La0.87 xLnxSr0.13FeAsO sample shows a superconducting hysteresis in addition to a paramagnetic background. The experiment demonstrates that the magnetism and superconductivity coexist in hole-doped FeAs-based superconducting compounds. Among these three magnetic rare-earth elements, the influence of Dy3 + doping on superconductivity is more evident than that of Gd3 + doping, while the influence of Sm3 + doping is the weakest. The trend is consistent with the variation of the lattice parameter along c-axis. & 2010 Elsevier Ltd. All rights reserved.
Keywords: A. Hole-doped superconductor A. Iron-based superconductor D. Paramagnetic D. Spin density wave
1. Introduction The recently discovered superconductivity in the iron-based layered compound LaFeAsO stimulates intensive studies in both fundamental research and potential application [1]. The superconducting transition temperature was raised to 55 K [2–5] shortly after substituting lanthanum with a number of other rareearth elements. So far most of the discovered superconductors are categorized into the so-called electron doped type. Wen et al. [6,] and Mu et al. [7] found that by partially substituting Sr2 + for La3 + in LaFeAsO, the resultant material La1 xSrxFeAsO became the first hole-doped superconductor in iron-based systems, but the highest transition temperature found is only 25 K. The presence of Fermi surface nesting may lead to SDW instability around 150 K and suppress the superconductivity. In an electron-doped superconductor of iron-based systems, the replacement of lanthanum by magnetic ions leads to deviation of the lattice parameter along c-axis further from the LaFeAsO phase and enhances the superconductivity. This is really surprising since rare-earth elements generally give rise to magnetic moments, and destroy the superconductivity. In the hole-doped superconducting system La1 xSrxFeAsO, the superconductivity is degraded by the substitution of La with Sm in the paper that we presented previously [8]. The result is completely different from that of the electron-doped system. In this paper, we substitute lanthanum with a number of other rare-earth elements to understand the
role of magnetic ions on the superconductivity in the hole-doped FeAs-based superconducting compounds.
2. Sample preparation and experiment A series of polycrystalline samples (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) were fabricated by the conventional solid state reaction method. The synthesis process includes two steps. First, La1 yLnyAs was prepared by reacting grains of La (purity 99.99%), Gd (purity 99.95%), Dy (purity 99.95%), Sm (purity 99.95%), and As grains (purity 99.999%) at 900 1C for 12 h, and then at 1180 1C for 40 h. They were sealed in an evacuated quartz tube during the reaction. The resultant pellet was then smashed and ground together with the FeAs power, SrO powder (purity 99.9%), Fe powder (purity 99.95%), and Fe2O3 powder (purity 99.5%) in stoichiometry as the formula (La0.87 xLnxSr0.13)FeAsO. Again, it was pressed into a pellet, sealed in an evacuated quartz tube, and burned at about 940 1C for 4 h, followed by burning at 1150–1200 1C for 48 h. It was finally cooled down slowly to room temperature. The quality and structure of the specimen were characterized by a Siemens D5000 power X-ray diffractometer using CuKa radiation at room temperature. The low field dc magnetic response and magnetic hysteresis loop were measured by a Quantum Design SQUID magnetometer.
3. Results and discussion n
Corresponding author. Tel.: + 886 4 22840427x396; fax: + 886 4 22850458. E-mail address: [email protected] (M.D. Lan).
0022-3697/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2010.10.013
In Fig. 1, we summarized the lattice constants along c-axis for all samples. The lattice parameters were determined by the
T.P. Lu et al. / Journal of Physics and Chemistry of Solids 72 (2011) 442–444
Fig. 1. Doping dependence of lattice constants along c-axis. The influence of Dy3 + doping is more evident than that of Gd3 + , while the influence of Sm3 + is the weakest among these three rare-earth elements.
443
method of least squares fit using 8 reflections in the powder X-ray diffraction patterns. The lattice constant along c-axis shrinks in comparison with the value of the (La0.87Sr0.13)FeAsO phase. But the lattice parameters along c-axis approach the value of the parent LaFeAsO phase, which is not superconducting. In addition, the influence of Dy3 + doping on the structure is more evident than that of Gd3 + doping, while the influence of Sm3 + doping is the weakest among these three rare-earth elements. This is reasonable since the radii of Sm3 + , Gd3 + , and Dy3 + are about 1.13, ˚ respectively, which are slightly smaller than that 1.11, and 1.07 A, ˚ of La3 + of about 1.15 A. In Fig. 2, we show the temperature dependence of resistivity for (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) samples. The superconducting transition temperature Tc decreases with increase in x for rare-earth element substitutions in the low temperature region. The inset shows the temperature dependence of dr/dT, it shows that Tc decreases with increase in x for rareearth element substitutions more clearly. In addition, with the same ratio of substitutions, we observed the influence of Dy3 + doping on Tc decreases is more evident than that by Gd3 + , while the influence of Sm3 + is the weakest. This doping dependence of Tc is quite similar to that in c-axis lattice constants. The influence of Tc and the structure of doping Dy3 + is more evident than others.
Fig. 2. Temperature dependence of dr/dT for (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) samples. Inset shows the temperature dependence of resistivity.
Fig. 3. Temperature dependence of magnetization measured for (La0.87 xLnxSr0.13) FeAsO (Ln¼Sm, Gd, Dy) samples under a 5 Oe applied field.
Fig. 4. (a) Magnetization hysteresis loops of La0.87 xGdxSr0.13FeAsO (x¼ 0, 0.04, and 0.06) samples measured at 5 K. Inset shows the enlarged view of initial magnetization in the low field region. (b) Magnetization hysteresis loops of La0.87 xDyxSr0.13FeAsO (x¼ 0, 0.04, and 0.06) samples measured at 5 K. Inset shows the enlarged view of initial magnetization in the low field region.
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T.P. Lu et al. / Journal of Physics and Chemistry of Solids 72 (2011) 442–444
This indicates that decrease in Tc is due to the shortness of the lattice constant along c-axis in the hole-doped system. Typical low-field magnetization responses for (La0.87 xLnxSr0.13)FeAsO (Ln¼Sm, Gd, Dy) samples under a 5 Oe applied field is shown in Fig. 3. In general, the superconducting transition temperature Tc decreases with increase in x for rare-earth element substitutions. The influence of Sm3+ doping is the weakest among these three magnetic rare-earth elements. We observed the onset of the superconducting transition temperature Tc in the La0.81Sm0.06Sr0.13FeAsO compound is higher than that in the La0.83Gd0.04Sr0.13FeAsO and La0.83Dy0.04 Sr0.13FeAsO compounds. The diamagnetic signal decreases with the composition of the rare-earth substitutions. The substitution of Dy3 + for La3+ is more efficient in destroying Tc. The transition temperature Tc determined from the magnetic response measurement is slightly lower than that determined from the resistivity measurement. Both trends of reducing Tc are consistent with the variation of lattice parameters, in particular, along the c-axis. Fig. 4(a) and (b) shows the magnetic hysteresis loops of (La0.87 xGdxSr0.13)FeAsO and (La0.87 xGdxSr0.13)FeAsO (x¼0, 0.04, and 0.06) samples at 5 K. The size of the superconducting loop in the (La0.87 xLnxSr0.13)FeAsO system is shrank with increase in x. The impressed feature shown in the figure is that the superconducting hysteresis loop of the La1 xSrxFeAsO compound is superimposed on the paramagnetic background. The paramagnetic signal increases with increase in concentration of rare-earth magnetic ions, but it is not significant for the La1 xSrxFeAsO compound. The result implies superconductivity can coexist with a small but non-negligible magnetic moment in hole-doped FeAs-based superconductors.
4. Conclusion In both electron-type and hole-type FeAs-based superconducting compounds, magnetism and superconductivity can coexist. The superconductivity is suppressed by increasing rare-earth
element substitutions in the hole-doped systems, which is quite different from the electron-doped systems. Besides, the influence of Dy3 + doping on superconductivity is more evident than that of Gd3 + doping, while the influence of Sm3 + doping is the weakest. The trend is consistent with the variation of the lattice parameter along c-axis. Meanwhile doping rare-earth elements in FeAs-based superconductors would lead to a change of the lattice parameter along c-axis. This could be the main reason for causing the reduction of Tc. The occurrence of spin-density-wave instability may play a more dominant role in the suppression of superconductivity in the hole-doped FeAs-based superconductor.
Acknowledgement This work was supported by the National Science Council of the Republic of China under Contract no. NSC 98-2112-M-005-007. References [1] Kamihara Yoichi, Watanabe Takumi, Hirano Masahiro, Hosono Hideo, J. Am. Chem. Soc. 130 (2008) 3296. [2] Zhi-An Ren, Wei Lu, Jie Yang, Wei Yi, Xiao-Li Shen, Zheng-Cai, Guang-Can Che, Xiao-Li Dong, Li-Ling Sun, Fang Zhou, Zhong-Xian Zhao, Chin. Phys. Lett. 25 (2008) 2215. [3] Peng Cheng, Lei Fang, Huan Yang, Xiyu Zhu, Gang Mu, Huiqian Luo, Zhaosheng Wang, Hai-Hu Wen, Sci. Chin. Phys. Mech. Astron. 51 (2008) 719. [4] Athena S. Sefat, Ashfia Huq, Michael A. McGuire, Rongying Jin, Brian C. Sales, David Mandrus, M.D.Cranswick Lachlan, W.Stephens Peter, H.Stone Kevin, Phys. Rev. B 78 (2008) 104505. [5] Guang-Can Zhi-An Ren, Xiao-Li Che, Jie Dong, Wei Yang, Wei Lu, Xiao-Li Yi, Zheng-Cai Shen, Li-Ling Li, Fang Sun, Zhong-Xian Zhao. Zhou, Europhys. Lett. 83 (2008) 17002. [6] Hai-Hu Wen, Gang Mu, Lei Fang, Huan Yang, Xiyu Zhu, Europhys. Lett. 82 (2008) 17009. [7] Gang Mu, Lei Fang, Huan Yang, Xiyu Zhu, Peng Cheng, Hai-Hu Wen, J. Phys. Soc. Jpn. 77 (2008) 15. [8] T.P. Lu, C.C. Wu, W.H. Chou, M.D. Lan, Physica C 470 (2010) 357–359.