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Superconductivity in ternary germanide Y(Pt0.5Ge1.5) with the AlB2-type structure
Physica C 377 (2002) 185–189 www.elsevier.com/locate/physc
Superconductivity in ternary germanide Y(Pt0:5Ge1:5) with the AlB2-type structure Hijiri Kit^ o
a,*
, Yoshihiko Takano
b,c
, Kazumasa Togano
b,c
a
c
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan b National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan Received 7 January 2002; accepted 15 March 2002
The authors dedicate this paper to Dr. H. Ihara of National Institute of Advanced Industrial Science and Technology who suddenly died on January 30, 2002
Abstract We have synthesized a new superconductor Y(Pt0:5 Ge1:5 ) by an arc-melting method. The average chemical analytical values were Y1:00ð3Þ [Pt0:67ð2Þ Ge1:305ð19Þ ]. Powder X-ray diffraction indicates that this compound has the AlB2 -type struc, c ¼ 3:9941(6) A and the unit-cell volume V is 60.90(3) A 3 . The ture. The lattice parameters are a ¼ 4:1959(7) A temperature dependence of electrical resistivity was measured between 1.8 K and room temperature. The onset temperature of the superconducting transition, Tc (onset) and the zero resistivity temperature, Tc (zero) were 3.3 K and 3.0 K, respectively. The magnetic susceptibility between 1.8 K and 10 K was measured as a function of temperature in various magnetic fields. Meissner effect was observed below 3.2 K. The magnetization versus magnetic field (M–H) curve was also measured at 1.8 K. These results show that Y(Pt0:5 Ge1:5 ) is a type II superconductor with a transition temperature of 3.3 K. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 61.10.Nz; 72.80.Ga; 74.25.Fy; 74.25.Ha; 74.62.)c; 74.70.)b; 74.72.Yg Keywords: Powder X-ray diffraction; AlB2 -type structure; Magnetic measurement; Resistivity measurement
1. Introduction Recently, high-temperature superconductivity in an intermetallic compound MgB2 (Tc 39 K) has been reported by Nagamatsu et al. [1]. After this
* Corresponding author. Tel.: +81-298-61-5119; fax: +81298-61-5447.
discovery, many studies have been performed for this compound [2–11]. MgB2 has the binary AlB2 type structure with P6/mmm. Therefore, the intermetallic compounds with this structure have attracted a lot of attention as the candidates for new high-temperature superconductors. The study on new superconductors with the AlB2 -type structure would contribute to understanding the origin of the high-temperature superconductivity in MgB2 .
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 1 3 3 1 - X
186
H. Kit^o et al. / Physica C 377 (2002) 185–189
Some silicides or germanides are known to crystallize with AlB2 -type structure [12–16]. Until now, several new superconductors have been reported in this series of compounds [17–19]. An interesting group of compounds is the ternary silicides or germanides, such as Er(Rh0:5 Si1:5 ) (2a; 2c) [20–22] and U(Ru0:5 Si1:5 ) (2a; c) [23], where the type of hexagonal ordering is given in parenthesis and refers to how the ordering has resulted in multiplication of the lattice constants of the AlB2 type structure. In these compounds, 4d element can be substituted for Si. We have searched for the superconducting materials in Y(Pt,Ge)2 system and have succeeded in the synthesis of a superconductor Y(Pt0:5 Ge1:5 ) for the first time. In this paper, we report the results of X-ray diffraction, electrical resistivity and dc magnetization measurements for this compound.
and 10 K was measured by using SQUID magnetometer (Quantum Design Co. Ltd.). The zero field cooling (ZFC) and the field cooling (FC) magnetization process were measured in an applied field of H ¼ 10 Oe, 100 Oe, 1 kOe and 10 kOe, respectively. The magnetization versus magnetic field curves (M–H curves) were measured at 1.8 K. 3. Results and discussion The powder X-ray diffraction pattern of the sample is shown in Fig. 1. Small amount of impurity phase with YPt2 Ge2 (ThCr2 Si2 ) type of
2. Experimental An Y(Pt0:5 Ge1:5 ) ingot with 1 g was prepared by arc-melting a 2:1:3 molar mixture of Y, Pt and Ge under pure Ar atmosphere. The melted button was turned over several times to homogenize. The losses in the melting process were less than 3% in weight. The chemical composition of the button was measured by SEM-EDX (JEOL JSM-630IF scanning microscope) using the obtained button. The average composition was estimated as Y1:00ð3Þ [Pt0:67ð2Þ Ge1:305ð19Þ ] which was measured nine points. Powder X-ray diffraction patterns were collected by Rigaku RINT 1000 diffractometer, using Cu Ka radiation equipped with a graphite monochrometer on the counter side. Intensity data were collected continuous scan mode and 2h range of 5–65.0° with an interval 1.20°/min. Lattice parameters were calculated by the least squares fitting of the powder X-ray diffraction patterns. Obtained samples YPt0:5 Ge1:5 were investigated by transport and magnetic measurements. The temperature dependence of the electrical resistivity qðT Þ was measured by the standard four probe AC method with applied current of 10 mA between 1.8 K and room temperature. Temperature dependence of the magnetic susceptibility between 1.8
Fig. 1. The powder X-ray diffraction patterns for Y(Pt0:5 Ge1:5 ). The unindexed lines, marked by , are ascribed to an impurity phase with YPt2 Ge2 (ThCr2 Si2 ) type structure.
Fig. 2. The temperature dependence of the electrical resistivity for Y(Pt0:5 Ge1:5 ) sample.
H. Kit^o et al. / Physica C 377 (2002) 185–189
structure are marked with . The superstructure lines coming from the ordering of 2d sites were not observed and the major phase can be indexed based on the disordered AlB2 -type hexagonal structure model (space group P6/mmm). Lattice , c ¼ 3:9941ð6Þ A parameters are a ¼ 4:1959ð7Þ A 3 . Maand unit-cell volume is V ¼ 60:90ð3Þ A jumdar and Sampathkumran reported AlB2 -type , c ¼ 4:000 A ) superconYPd0:5 Ge1:5 (a ¼ 4:192 A
187
ductor (Tc ¼ 3:0 K) [17]. These values are close to those for isostructural YPd0:5 Ge1:5 and are larger , c ¼ 3:404(1) than those for MgB2 (a ¼ 3:047(1) A A) single crystal [10]. The interatomic distance between Y atom and . The 2d site is the posithe 2d site is 3.1395(4) A tion at the center of a triangle prism of six Y atoms where Pt and Ge are chemically disordered with the occupation probabilities of 0.335 for Pt and
Fig. 3. (a) The temperature dependence of the magnetic susceptibility for Y(Pt0:5 Ge1:5 ) in various applied fields. The open circle, open square, open diamond and open triangle show in ZFC data and solid circle, solid square, solid diamond and solid triangle show data in FC states, respectively. (b) M–H curves for Y(Pt0:5 Ge1:5 ) at 1.8 K.
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H. Kit^o et al. / Physica C 377 (2002) 185–189
0.6525 for Ge atoms. Here, to discuss the interatomic distance for the intermetallic compound is appropriate using the atomic radii than using the ionic radii. According to Pauling [24], the atomic radii in metals for XII Y, VI Ge and VI Pt, are 1.797, , respectively, where the roman 1.276 and 1.295 A numerals denote the coordination number. Using these value, we obtained the interatomic distance for Y–(Pt0:335 Ge0:6525 ). The value of the of 3.063 A mean distance is comparable with that of the estimated distance. The electrical resistivity q is shown as a function of temperature in Fig. 2. The room temperature resistivity qðRTÞ has a value of 0.44 mX cm. The resistivity decreases gradually with decreasing temperature down to 3.3 K and the resistivity at 3.3 K ðqð3:3 KÞÞ is 0.25 mX cm, giving the residual resistivity ratio qðRTÞ=qð3:3 KÞ of 1.8. From the resistivity data, Tc (onset) and Tc (zero) are 3.3 and 3.0 K, respectively. The value of Tc of this material is very close to that of Y(Pd0:5 Ge1:5 ) superconductor [17] and lower than that of a-ThSi2 type YGe2 superconductor (Tc ¼ 3:8 K) [25]. Fig. 3(a) shows the temperature dependence of the magnetic susceptibility in various applied fields. The diamagnetic behavior was observed below 3.2 K in a magnetic field H ¼ 10 Oe. The transition temperature decreases with increasing magnetic field. The theoretical density was estimated to be 8.05 g/cm3 from the chemical composition and lattice parameters. The Meissner volume fraction in ZFC and FC at 1.8 K are calculated to be about 63.8% and 0.23%, respectively. This result indicates that the material has a fairly large flux pinning force resulting in the trapping of magnetic flux in the FC condition similar to the large flux pinning of MgB2 [6]. The M–H curves of the sample at 1.8 K are shown in Fig. 3(b). This shows the characteristic curve of type II superconductor. From M–H curves, we tried to determine the lower critical field (Hc1 ). The Hc1 was defined as the magnetic field, at which the initial slope meets the extrapolation curve of ðMup þ Mdown Þ=2 and was given about 50 Oe at 1.8 K. This study would stimulate the study of superconductors with the AlB2 -type structure, and could be helpful for understanding the origin of high-temperature superconductivity in MgB2 .
In conclusion, we have synthesized new member of ternary germanide Y(Pt0:5 Ge1:5 ) superconductor (Tc ¼ 3:3 K) by arc-melting technique. The crystal structure of Y(Pt0:5 Ge1:5 ) is the AlB2 -type structure. Values of lattice parameters for the new superconducting material Y(Pt0:5 Ge1:5 ) are close to those for Y(Pd0:5 Ge1:5 ) superconductor (Tc ¼ 3:0 K) [17]. Acknowledgements The authors would like to express their special thanks for useful information and helpful discussions to Dr. Akiyuki Matsushita, Dr. Hideaki Kitazawa and Dr. Hideki Abe of National Institute for Materials Sciences.
References [1] J. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani, J. Akimitsu, Nature 410 (2001) 63. [2] S.L. Bud’ko, G. Lapertot, C. Petrovic, C.E. Cunningham, N. Anderson, P.C. Canfield, Phys. Rev. Lett. 86 (2001) 1877. [3] D.K. Finnemore, J.E. Ostenson, S.L. Bud’ko, G. Lapertot, P.C. Canfield, Phys. Rev. Lett. 86 (2001) 2420. [4] J.S. Slusky, N. Rogado, K.A. Regan, M.A. Hayward, P. Khalifah, T. He, K. Inumaru, S.M. Loureiro, M.K. Haas, H.W. Zandbergen, R.J. Cava, Nature 410 (2001) 343. [5] P.C. Canfield, D.K. Finnemore, S.L. Bud’ko, J.E. Ostenson, G. Lapertot, C.E. Cunningham, C. Petrovic, Phys. Rev. Lett. 86 (2001) 2423. [6] Y. Takano, H. Takeya, H. Fujii, H. Kumakura, T. Hatano, K. Togano, H. Kito, H. Ihara, Appl. Phys. Lett. 78 (2001) 2914. [7] G. Rubio-Bollinger, H. Suderow, S. Vieira, Phys. Rev. Lett. 86 (2001) 5582. [8] J.D. Jorgensen, D.G. Hinks, S. Short, Phys. Rev. B 63 (2001) 224522. [9] K. Prassides, Y. Iwasa, T. Ito, D.H. Chi, K. Uehara, E. Nishibori, M. Takata, M. Sakata, Y. Ohishi, O. Shimomura, T. Muranaka, J. Akimitsu, Phys. Rev. B 64 (2001) 012509. [10] M. Xu, H. Kitazawa, Y. Takano, J. Ye, K. Nishida, H. Abe, A. Matsushita, N. Tsujii, G. Kido, Appl. Phys. Lett. 79 (2001) 2779. [11] H. Kumakura, Y. Takano, H. Fujii, K. Togano, H. Kit^ o, H. Ihara, Physica C 363 (2001) 179. [12] W.H. Zachariasen, Acta Crystallogr. 2 (1949) 94. [13] A. Brown, J.J. Norreys, Nature 183 (1959) 673. [14] F.A. Schmidt, O.D. McMasters, O.N. Carlson, J. LessCommon. Metals 26 (1972) 53.
H. Kit^o et al. / Physica C 377 (2002) 185–189 [15] A.V. Morozkin, Yu.D. Seropegin, O.I. Bodak, J. Alloys Comp. 234 (1996) 143. [16] P. Salamakha, M. Konyk, O. Sologub, O.I. Bodak, J. Alloys Comp. 236 (1996) 206. [17] S. Majumdar, E.V. Sampathkumaran, Phys. Rev. B 63 (2001) 172407. [18] M. Imai, E. Abe, J. Ye, K. Nishida, T. Kimura, K. Honma, H. Abe, H. Kitazawa, Phys. Rev. Lett. 87 (2001) 077003. [19] S. Ohba, K. Satoh, T. Muranaka, Y. Zenitani, J. Akimitsu, in: Conference of the Japanese Physical Society, vol. 28, 2001, p. PSA-44.
189
[20] B. Chevalier, P. Lejay, J. Etourneau, P. Hagenmuller, Solid State Commun. 49 (1984) 753. [21] P.A. Kotsanidis, J.K. Yakinthos, E. Gamari-Seale, J. Magn. Magn. Mater. 87 (1990) 199. [22] R.E. Gladyshevskii, K. Cenzual, E. Parthe, J. Alloys Comp. 189 (1992) 221. [23] R. P€ ottgen, P. Gravereau, B. Darriet, B. Chevalier, E. Hickey, J. Etourneau, J. Mater. Chem. 4 (1994) 463. [24] L. Pauling, J. Am. Chem. Soc. 69 (1947) 542. [25] B.T. Matthias, E. Crenzwit, W.H. Zachariasen, Phys. Rev. 112 (1958) 89.
Superconductivity in ternary germanide Y(Pt0:5Ge1:5) with the AlB2-type structure Hijiri Kit^ o
a,*
, Yoshihiko Takano
b,c
, Kazumasa Togano
b,c
a
c
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan b National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan Received 7 January 2002; accepted 15 March 2002
The authors dedicate this paper to Dr. H. Ihara of National Institute of Advanced Industrial Science and Technology who suddenly died on January 30, 2002
Abstract We have synthesized a new superconductor Y(Pt0:5 Ge1:5 ) by an arc-melting method. The average chemical analytical values were Y1:00ð3Þ [Pt0:67ð2Þ Ge1:305ð19Þ ]. Powder X-ray diffraction indicates that this compound has the AlB2 -type struc, c ¼ 3:9941(6) A and the unit-cell volume V is 60.90(3) A 3 . The ture. The lattice parameters are a ¼ 4:1959(7) A temperature dependence of electrical resistivity was measured between 1.8 K and room temperature. The onset temperature of the superconducting transition, Tc (onset) and the zero resistivity temperature, Tc (zero) were 3.3 K and 3.0 K, respectively. The magnetic susceptibility between 1.8 K and 10 K was measured as a function of temperature in various magnetic fields. Meissner effect was observed below 3.2 K. The magnetization versus magnetic field (M–H) curve was also measured at 1.8 K. These results show that Y(Pt0:5 Ge1:5 ) is a type II superconductor with a transition temperature of 3.3 K. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 61.10.Nz; 72.80.Ga; 74.25.Fy; 74.25.Ha; 74.62.)c; 74.70.)b; 74.72.Yg Keywords: Powder X-ray diffraction; AlB2 -type structure; Magnetic measurement; Resistivity measurement
1. Introduction Recently, high-temperature superconductivity in an intermetallic compound MgB2 (Tc 39 K) has been reported by Nagamatsu et al. [1]. After this
* Corresponding author. Tel.: +81-298-61-5119; fax: +81298-61-5447.
discovery, many studies have been performed for this compound [2–11]. MgB2 has the binary AlB2 type structure with P6/mmm. Therefore, the intermetallic compounds with this structure have attracted a lot of attention as the candidates for new high-temperature superconductors. The study on new superconductors with the AlB2 -type structure would contribute to understanding the origin of the high-temperature superconductivity in MgB2 .
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 1 3 3 1 - X
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H. Kit^o et al. / Physica C 377 (2002) 185–189
Some silicides or germanides are known to crystallize with AlB2 -type structure [12–16]. Until now, several new superconductors have been reported in this series of compounds [17–19]. An interesting group of compounds is the ternary silicides or germanides, such as Er(Rh0:5 Si1:5 ) (2a; 2c) [20–22] and U(Ru0:5 Si1:5 ) (2a; c) [23], where the type of hexagonal ordering is given in parenthesis and refers to how the ordering has resulted in multiplication of the lattice constants of the AlB2 type structure. In these compounds, 4d element can be substituted for Si. We have searched for the superconducting materials in Y(Pt,Ge)2 system and have succeeded in the synthesis of a superconductor Y(Pt0:5 Ge1:5 ) for the first time. In this paper, we report the results of X-ray diffraction, electrical resistivity and dc magnetization measurements for this compound.
and 10 K was measured by using SQUID magnetometer (Quantum Design Co. Ltd.). The zero field cooling (ZFC) and the field cooling (FC) magnetization process were measured in an applied field of H ¼ 10 Oe, 100 Oe, 1 kOe and 10 kOe, respectively. The magnetization versus magnetic field curves (M–H curves) were measured at 1.8 K. 3. Results and discussion The powder X-ray diffraction pattern of the sample is shown in Fig. 1. Small amount of impurity phase with YPt2 Ge2 (ThCr2 Si2 ) type of
2. Experimental An Y(Pt0:5 Ge1:5 ) ingot with 1 g was prepared by arc-melting a 2:1:3 molar mixture of Y, Pt and Ge under pure Ar atmosphere. The melted button was turned over several times to homogenize. The losses in the melting process were less than 3% in weight. The chemical composition of the button was measured by SEM-EDX (JEOL JSM-630IF scanning microscope) using the obtained button. The average composition was estimated as Y1:00ð3Þ [Pt0:67ð2Þ Ge1:305ð19Þ ] which was measured nine points. Powder X-ray diffraction patterns were collected by Rigaku RINT 1000 diffractometer, using Cu Ka radiation equipped with a graphite monochrometer on the counter side. Intensity data were collected continuous scan mode and 2h range of 5–65.0° with an interval 1.20°/min. Lattice parameters were calculated by the least squares fitting of the powder X-ray diffraction patterns. Obtained samples YPt0:5 Ge1:5 were investigated by transport and magnetic measurements. The temperature dependence of the electrical resistivity qðT Þ was measured by the standard four probe AC method with applied current of 10 mA between 1.8 K and room temperature. Temperature dependence of the magnetic susceptibility between 1.8
Fig. 1. The powder X-ray diffraction patterns for Y(Pt0:5 Ge1:5 ). The unindexed lines, marked by , are ascribed to an impurity phase with YPt2 Ge2 (ThCr2 Si2 ) type structure.
Fig. 2. The temperature dependence of the electrical resistivity for Y(Pt0:5 Ge1:5 ) sample.
H. Kit^o et al. / Physica C 377 (2002) 185–189
structure are marked with . The superstructure lines coming from the ordering of 2d sites were not observed and the major phase can be indexed based on the disordered AlB2 -type hexagonal structure model (space group P6/mmm). Lattice , c ¼ 3:9941ð6Þ A parameters are a ¼ 4:1959ð7Þ A 3 . Maand unit-cell volume is V ¼ 60:90ð3Þ A jumdar and Sampathkumran reported AlB2 -type , c ¼ 4:000 A ) superconYPd0:5 Ge1:5 (a ¼ 4:192 A
187
ductor (Tc ¼ 3:0 K) [17]. These values are close to those for isostructural YPd0:5 Ge1:5 and are larger , c ¼ 3:404(1) than those for MgB2 (a ¼ 3:047(1) A A) single crystal [10]. The interatomic distance between Y atom and . The 2d site is the posithe 2d site is 3.1395(4) A tion at the center of a triangle prism of six Y atoms where Pt and Ge are chemically disordered with the occupation probabilities of 0.335 for Pt and
Fig. 3. (a) The temperature dependence of the magnetic susceptibility for Y(Pt0:5 Ge1:5 ) in various applied fields. The open circle, open square, open diamond and open triangle show in ZFC data and solid circle, solid square, solid diamond and solid triangle show data in FC states, respectively. (b) M–H curves for Y(Pt0:5 Ge1:5 ) at 1.8 K.
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H. Kit^o et al. / Physica C 377 (2002) 185–189
0.6525 for Ge atoms. Here, to discuss the interatomic distance for the intermetallic compound is appropriate using the atomic radii than using the ionic radii. According to Pauling [24], the atomic radii in metals for XII Y, VI Ge and VI Pt, are 1.797, , respectively, where the roman 1.276 and 1.295 A numerals denote the coordination number. Using these value, we obtained the interatomic distance for Y–(Pt0:335 Ge0:6525 ). The value of the of 3.063 A mean distance is comparable with that of the estimated distance. The electrical resistivity q is shown as a function of temperature in Fig. 2. The room temperature resistivity qðRTÞ has a value of 0.44 mX cm. The resistivity decreases gradually with decreasing temperature down to 3.3 K and the resistivity at 3.3 K ðqð3:3 KÞÞ is 0.25 mX cm, giving the residual resistivity ratio qðRTÞ=qð3:3 KÞ of 1.8. From the resistivity data, Tc (onset) and Tc (zero) are 3.3 and 3.0 K, respectively. The value of Tc of this material is very close to that of Y(Pd0:5 Ge1:5 ) superconductor [17] and lower than that of a-ThSi2 type YGe2 superconductor (Tc ¼ 3:8 K) [25]. Fig. 3(a) shows the temperature dependence of the magnetic susceptibility in various applied fields. The diamagnetic behavior was observed below 3.2 K in a magnetic field H ¼ 10 Oe. The transition temperature decreases with increasing magnetic field. The theoretical density was estimated to be 8.05 g/cm3 from the chemical composition and lattice parameters. The Meissner volume fraction in ZFC and FC at 1.8 K are calculated to be about 63.8% and 0.23%, respectively. This result indicates that the material has a fairly large flux pinning force resulting in the trapping of magnetic flux in the FC condition similar to the large flux pinning of MgB2 [6]. The M–H curves of the sample at 1.8 K are shown in Fig. 3(b). This shows the characteristic curve of type II superconductor. From M–H curves, we tried to determine the lower critical field (Hc1 ). The Hc1 was defined as the magnetic field, at which the initial slope meets the extrapolation curve of ðMup þ Mdown Þ=2 and was given about 50 Oe at 1.8 K. This study would stimulate the study of superconductors with the AlB2 -type structure, and could be helpful for understanding the origin of high-temperature superconductivity in MgB2 .
In conclusion, we have synthesized new member of ternary germanide Y(Pt0:5 Ge1:5 ) superconductor (Tc ¼ 3:3 K) by arc-melting technique. The crystal structure of Y(Pt0:5 Ge1:5 ) is the AlB2 -type structure. Values of lattice parameters for the new superconducting material Y(Pt0:5 Ge1:5 ) are close to those for Y(Pd0:5 Ge1:5 ) superconductor (Tc ¼ 3:0 K) [17]. Acknowledgements The authors would like to express their special thanks for useful information and helpful discussions to Dr. Akiyuki Matsushita, Dr. Hideaki Kitazawa and Dr. Hideki Abe of National Institute for Materials Sciences.
References [1] J. Nagamatsu, N. Nakagawa, T. Muranaka, Y. Zenitani, J. Akimitsu, Nature 410 (2001) 63. [2] S.L. Bud’ko, G. Lapertot, C. Petrovic, C.E. Cunningham, N. Anderson, P.C. Canfield, Phys. Rev. Lett. 86 (2001) 1877. [3] D.K. Finnemore, J.E. Ostenson, S.L. Bud’ko, G. Lapertot, P.C. Canfield, Phys. Rev. Lett. 86 (2001) 2420. [4] J.S. Slusky, N. Rogado, K.A. Regan, M.A. Hayward, P. Khalifah, T. He, K. Inumaru, S.M. Loureiro, M.K. Haas, H.W. Zandbergen, R.J. Cava, Nature 410 (2001) 343. [5] P.C. Canfield, D.K. Finnemore, S.L. Bud’ko, J.E. Ostenson, G. Lapertot, C.E. Cunningham, C. Petrovic, Phys. Rev. Lett. 86 (2001) 2423. [6] Y. Takano, H. Takeya, H. Fujii, H. Kumakura, T. Hatano, K. Togano, H. Kito, H. Ihara, Appl. Phys. Lett. 78 (2001) 2914. [7] G. Rubio-Bollinger, H. Suderow, S. Vieira, Phys. Rev. Lett. 86 (2001) 5582. [8] J.D. Jorgensen, D.G. Hinks, S. Short, Phys. Rev. B 63 (2001) 224522. [9] K. Prassides, Y. Iwasa, T. Ito, D.H. Chi, K. Uehara, E. Nishibori, M. Takata, M. Sakata, Y. Ohishi, O. Shimomura, T. Muranaka, J. Akimitsu, Phys. Rev. B 64 (2001) 012509. [10] M. Xu, H. Kitazawa, Y. Takano, J. Ye, K. Nishida, H. Abe, A. Matsushita, N. Tsujii, G. Kido, Appl. Phys. Lett. 79 (2001) 2779. [11] H. Kumakura, Y. Takano, H. Fujii, K. Togano, H. Kit^ o, H. Ihara, Physica C 363 (2001) 179. [12] W.H. Zachariasen, Acta Crystallogr. 2 (1949) 94. [13] A. Brown, J.J. Norreys, Nature 183 (1959) 673. [14] F.A. Schmidt, O.D. McMasters, O.N. Carlson, J. LessCommon. Metals 26 (1972) 53.
H. Kit^o et al. / Physica C 377 (2002) 185–189 [15] A.V. Morozkin, Yu.D. Seropegin, O.I. Bodak, J. Alloys Comp. 234 (1996) 143. [16] P. Salamakha, M. Konyk, O. Sologub, O.I. Bodak, J. Alloys Comp. 236 (1996) 206. [17] S. Majumdar, E.V. Sampathkumaran, Phys. Rev. B 63 (2001) 172407. [18] M. Imai, E. Abe, J. Ye, K. Nishida, T. Kimura, K. Honma, H. Abe, H. Kitazawa, Phys. Rev. Lett. 87 (2001) 077003. [19] S. Ohba, K. Satoh, T. Muranaka, Y. Zenitani, J. Akimitsu, in: Conference of the Japanese Physical Society, vol. 28, 2001, p. PSA-44.
189
[20] B. Chevalier, P. Lejay, J. Etourneau, P. Hagenmuller, Solid State Commun. 49 (1984) 753. [21] P.A. Kotsanidis, J.K. Yakinthos, E. Gamari-Seale, J. Magn. Magn. Mater. 87 (1990) 199. [22] R.E. Gladyshevskii, K. Cenzual, E. Parthe, J. Alloys Comp. 189 (1992) 221. [23] R. P€ ottgen, P. Gravereau, B. Darriet, B. Chevalier, E. Hickey, J. Etourneau, J. Mater. Chem. 4 (1994) 463. [24] L. Pauling, J. Am. Chem. Soc. 69 (1947) 542. [25] B.T. Matthias, E. Crenzwit, W.H. Zachariasen, Phys. Rev. 112 (1958) 89.