- Email: [email protected]
Co substitution
ARTICLE IN PRESS
Physica B 359–361 (2005) 1081–1083 www.elsevier.com/locate/physb
Quenching of PuCoGa5 superconducting parameters by Fe/Co and Ni/Co substitution Pascal Bouleta,, Eric Colineaua, Franck Wastina, Pavel Javorsky´a,b, Jean Rebizanta a
Institute for Transuranium Elements, Joint Research Centre, European Commission, Postfach 2340, D-76125 Karlsruhe, Germany b Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Prague 2, The Czech Republic
Abstract The magnetic and electronic investigations of PuCo1xTxGa5 compounds, with x ¼ 0:1 and 0.2 for T ¼ Fe and x ¼ 0:1 for Ni, are carried out by magnetization and specific heat measurements. Whereas comparison of the results obtained on the CeCo1xRhxIn5 and PuCo1xRhxGa5 series revealed strong correlation between the superconducting temperature transition and the unit cell ratio c/a in this structure, it is shown that in the cases of Fe and Ni, Tc is suppressed faster than when replacing Co by Rh. This observation reveals the crucial role in bonding and hybridization of the 5f electrons with the neighboring elements. r 2005 Elsevier B.V. All rights reserved. PACS: 74.62.Bf; 74.25.B; 74.70.Tx Keywords: Superconductivity; Plutonium; Actinides
1. Introduction The unusual properties of plutonium make it one of the most interesting and puzzling elements in the periodic table. As illustrated by its six different allotropic phases, plutonium is extremely sensitive to change in temperature, pressure or chemistry. As a consequence, its reactivity allows Corresponding author. Fax: +49 7247 951 99645.
E-mail address: [email protected] (P. Boulet).
the formation of many compounds, which show interesting chemical and physical properties. Recently, the discovery of superconductivity in the intermetallic compounds PuTGa5 with T ¼ Co [1] and Rh [2] raised new interest amongst the scientific community. The similarities with the unconventional isostructural Ce-based compounds CeMIn5 and, more particularly, the comparison of the CeCo1xRhxIn5 and PuCo1xRhxGa5 systems has recently revealed a similar variation of Tc versus c/a [3,4], with in both cases a DT c =Dðc=aÞ
0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.01.338
ARTICLE IN PRESS P. Boulet et al. / Physica B 359– 361 (2005) 1081–1083
100; indicating a common underlying physics and the importance of anisotropy in the establishment of superconductivity in this structure. In this frame, we present here the magnetic and electronic properties of PuCo1xTxGa5 compounds with x ¼ 0:1 and 0.2 for T ¼ Fe and x ¼ 0:1 for Ni using SQUID magnetometry and specific heat measurements.
2. Results Although pure PuFeGa5 and PuNiGa5 compounds have not been obtained yet, a complete solid solution of PuCo1xTxGa5 can be prepared by annealing the arc-melted sample at 850 1C for two weeks. It may be highlighted that such solid solutions with Fe and Ni could not be obtained in the Ce systems, indicating that the plutonium 1–1–5 phase presents a larger stability. The crystal structure and the purity of the polycrystalline samples obtained were then checked by X-ray diffraction. Similar to the Co–Rh solid solution, the variation of the lattice parameters does not follow Vegard’s law, indicating that steric effect is not the only parameter involved in the stability of this crystal structure. However, the c/a versus concentration, where a and c are the tetragonal lattice parameters, shows a linear relation, indicating a constant increase of the anisotropy as x increases in this structure.
The magnetization measurements, displayed in Fig. 1, indicate, as observed for PuCoGa5, that PuCo0.9Fe0.1Ga5, PuCo0.8Fe0.2Ga5 and PuCo0.9Ni0.1Ga5 show the onset of a superconducting transition at 13.4, 9.9 and 16.4 K, respectively. Confirming the magnetization data, the specific heat measurement performed on the PuCo0.9Fe0.1Ga5 compound (Fig. 2) shows the bulk nature of the superconducting transition taking place around 13 K. By comparison with the pure compound, 0.5 PuCoGa5 0.4 Cp /T (J/mol.K2 )
1082
0.3
Pu(Co0.9Fe0.1)Ga5
0.2 0.1 0.0 6
8
10 12 14 Te mperature (K)
16
18
20
Fig. 2. Specific heat measurement of PuCo0.9Fe0.1Ga5 and PuCoGa5 under 9, 4 and 0 T.
c/a of P uT'1-xT''xGa 5 1.59 4
1.596
1.5 98
1.60 0
1.602
1.604
2.5
1.606 20
Pu Co 0.5 Rh 0.5 Ga 5
PuCo0.9Ni0.1Ga5
PuCo0.9Fe0.1Ga5
-40 -60
CeRh 0.5 Ir0.5 In5 CeRh 0.25 Ir0. 75 In5
PuCoGa5
-80
0.5
CeIr In 5
Pu Co 0.9 Fe 0. 1 Ga 5
12
CeCo 0.5 Ir0.5 In5 10
Pu Co 0.1 Rh 0.9 Ga 5
Pu Co 0.8 Fe 0.2 Ga 5
Pu RhGa 5
-100
16
14
1.0
PuCo0.8Fe0.2Ga5
Pu Co 0.9 Ni0. 1 Ga 5
CeCo 0.5 Rh 0.5 In5
1.5
18
Tc(K)
-20
Pu CoGa 5
2.0
0 Tc(K)
Magnetisation(emu/Pu mol)
CeCoIn 5
8
0.0 1.61 0
-120 4
8
12 16 Temperature (K)
20
24
Fig. 1. Zero-field cooled (ZFC) and field-cooled (FC) magnetization of PuCo1xTxGa5 measured at B ¼ 0:001 T: x ¼ 0 (triangles), with T ¼ Fe; x ¼ 0:1 (circles), x ¼ 0:2 (squares) and T ¼ Ni; x ¼ 0:1 (diamonds).
1.615
1.6 20
1.62 5
1.630
1.635
1.640
c/a of CeT' 1-xT''xIn5
Fig. 3. Superconducting transition temperature Tc for a series of PuCo1xTxGa5-based compounds (right ordinate) and for isostructural Ce-based compounds (left ordinate). The circle corresponds to Co–Rh, the square to Co–Fe and the triangle to Co–Ni solid solutions.
ARTICLE IN PRESS P. Boulet et al. / Physica B 359– 361 (2005) 1081–1083
one notices a similar behavior with a slightly enhanced g ¼ 90 mJ=mol K2 extrapolated from the normal state. These new results can be compared with those already obtained with the Co–Rh solid solutions in the Ce and Pu system. As displayed in Fig. 3, a similar DT c =Dðc=aÞ 100 are observed in both CeCo1xRhxIn5 and PuCo1xRhxGa5 systems [3]. In the case of Fe and probably also in the case of Ni, the slope strongly increases, evidencing first a non-trivial relation between c/a and Tc and second the influence of the transition metal, although this later is not included in the first coordination sphere of plutonium. The comparison with Pu-substitution by U or Np [5] reveals that in the case of the transition metal substitution this latter has less influence on the critical superconducting parameters, which somewhat confirms that superconductivity in PuCoGa5 is emerging out of electronic states dominated by the Pu 5f electrons.
1083
Acknowledgements We are grateful to J.D. Thompson for fruitful discussions. P.J. acknowledges the European Commission for support in the frame of the ‘‘Training and Mobility of Researchers’’ program.
References [1] J.L. Sarrao, L.A. Morales, J.D. Thompson, B.L. Scott, G.R. Stewart, F. Wastin, J. Rebizant, P. Boulet, E. Colineau, G.H. Lander, Nature (London) 420 (2002) 297. [2] F. Wastin, P. Boulet, J. Rebizant, E. Colineau, G.H. Lander, J. Phys.: Condens. Matter 15 (2003) 2279. [3] J.D. Thompson, J.L. Sarrao, L.A. Morales, F. Wastin, P. Boulet, Physica C 412 (2004) 10. [4] E.D. Bauer, J.D. Thompson, J.L. Sarrao, L.A. Moraloes, F. Wastin, J. Rebizant, et al., Phys. Rev. Lett. 93 (2004) 147005. [5] E. Colineau, F. Wastin, P. Boulet, P. Javorsky, J. Rebizant, this conference, doi:10.1016/j.physb.2005.01.291.
Physica B 359–361 (2005) 1081–1083 www.elsevier.com/locate/physb
Quenching of PuCoGa5 superconducting parameters by Fe/Co and Ni/Co substitution Pascal Bouleta,, Eric Colineaua, Franck Wastina, Pavel Javorsky´a,b, Jean Rebizanta a
Institute for Transuranium Elements, Joint Research Centre, European Commission, Postfach 2340, D-76125 Karlsruhe, Germany b Department of Electronic Structures, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Prague 2, The Czech Republic
Abstract The magnetic and electronic investigations of PuCo1xTxGa5 compounds, with x ¼ 0:1 and 0.2 for T ¼ Fe and x ¼ 0:1 for Ni, are carried out by magnetization and specific heat measurements. Whereas comparison of the results obtained on the CeCo1xRhxIn5 and PuCo1xRhxGa5 series revealed strong correlation between the superconducting temperature transition and the unit cell ratio c/a in this structure, it is shown that in the cases of Fe and Ni, Tc is suppressed faster than when replacing Co by Rh. This observation reveals the crucial role in bonding and hybridization of the 5f electrons with the neighboring elements. r 2005 Elsevier B.V. All rights reserved. PACS: 74.62.Bf; 74.25.B; 74.70.Tx Keywords: Superconductivity; Plutonium; Actinides
1. Introduction The unusual properties of plutonium make it one of the most interesting and puzzling elements in the periodic table. As illustrated by its six different allotropic phases, plutonium is extremely sensitive to change in temperature, pressure or chemistry. As a consequence, its reactivity allows Corresponding author. Fax: +49 7247 951 99645.
E-mail address: [email protected] (P. Boulet).
the formation of many compounds, which show interesting chemical and physical properties. Recently, the discovery of superconductivity in the intermetallic compounds PuTGa5 with T ¼ Co [1] and Rh [2] raised new interest amongst the scientific community. The similarities with the unconventional isostructural Ce-based compounds CeMIn5 and, more particularly, the comparison of the CeCo1xRhxIn5 and PuCo1xRhxGa5 systems has recently revealed a similar variation of Tc versus c/a [3,4], with in both cases a DT c =Dðc=aÞ
0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2005.01.338
ARTICLE IN PRESS P. Boulet et al. / Physica B 359– 361 (2005) 1081–1083
100; indicating a common underlying physics and the importance of anisotropy in the establishment of superconductivity in this structure. In this frame, we present here the magnetic and electronic properties of PuCo1xTxGa5 compounds with x ¼ 0:1 and 0.2 for T ¼ Fe and x ¼ 0:1 for Ni using SQUID magnetometry and specific heat measurements.
2. Results Although pure PuFeGa5 and PuNiGa5 compounds have not been obtained yet, a complete solid solution of PuCo1xTxGa5 can be prepared by annealing the arc-melted sample at 850 1C for two weeks. It may be highlighted that such solid solutions with Fe and Ni could not be obtained in the Ce systems, indicating that the plutonium 1–1–5 phase presents a larger stability. The crystal structure and the purity of the polycrystalline samples obtained were then checked by X-ray diffraction. Similar to the Co–Rh solid solution, the variation of the lattice parameters does not follow Vegard’s law, indicating that steric effect is not the only parameter involved in the stability of this crystal structure. However, the c/a versus concentration, where a and c are the tetragonal lattice parameters, shows a linear relation, indicating a constant increase of the anisotropy as x increases in this structure.
The magnetization measurements, displayed in Fig. 1, indicate, as observed for PuCoGa5, that PuCo0.9Fe0.1Ga5, PuCo0.8Fe0.2Ga5 and PuCo0.9Ni0.1Ga5 show the onset of a superconducting transition at 13.4, 9.9 and 16.4 K, respectively. Confirming the magnetization data, the specific heat measurement performed on the PuCo0.9Fe0.1Ga5 compound (Fig. 2) shows the bulk nature of the superconducting transition taking place around 13 K. By comparison with the pure compound, 0.5 PuCoGa5 0.4 Cp /T (J/mol.K2 )
1082
0.3
Pu(Co0.9Fe0.1)Ga5
0.2 0.1 0.0 6
8
10 12 14 Te mperature (K)
16
18
20
Fig. 2. Specific heat measurement of PuCo0.9Fe0.1Ga5 and PuCoGa5 under 9, 4 and 0 T.
c/a of P uT'1-xT''xGa 5 1.59 4
1.596
1.5 98
1.60 0
1.602
1.604
2.5
1.606 20
Pu Co 0.5 Rh 0.5 Ga 5
PuCo0.9Ni0.1Ga5
PuCo0.9Fe0.1Ga5
-40 -60
CeRh 0.5 Ir0.5 In5 CeRh 0.25 Ir0. 75 In5
PuCoGa5
-80
0.5
CeIr In 5
Pu Co 0.9 Fe 0. 1 Ga 5
12
CeCo 0.5 Ir0.5 In5 10
Pu Co 0.1 Rh 0.9 Ga 5
Pu Co 0.8 Fe 0.2 Ga 5
Pu RhGa 5
-100
16
14
1.0
PuCo0.8Fe0.2Ga5
Pu Co 0.9 Ni0. 1 Ga 5
CeCo 0.5 Rh 0.5 In5
1.5
18
Tc(K)
-20
Pu CoGa 5
2.0
0 Tc(K)
Magnetisation(emu/Pu mol)
CeCoIn 5
8
0.0 1.61 0
-120 4
8
12 16 Temperature (K)
20
24
Fig. 1. Zero-field cooled (ZFC) and field-cooled (FC) magnetization of PuCo1xTxGa5 measured at B ¼ 0:001 T: x ¼ 0 (triangles), with T ¼ Fe; x ¼ 0:1 (circles), x ¼ 0:2 (squares) and T ¼ Ni; x ¼ 0:1 (diamonds).
1.615
1.6 20
1.62 5
1.630
1.635
1.640
c/a of CeT' 1-xT''xIn5
Fig. 3. Superconducting transition temperature Tc for a series of PuCo1xTxGa5-based compounds (right ordinate) and for isostructural Ce-based compounds (left ordinate). The circle corresponds to Co–Rh, the square to Co–Fe and the triangle to Co–Ni solid solutions.
ARTICLE IN PRESS P. Boulet et al. / Physica B 359– 361 (2005) 1081–1083
one notices a similar behavior with a slightly enhanced g ¼ 90 mJ=mol K2 extrapolated from the normal state. These new results can be compared with those already obtained with the Co–Rh solid solutions in the Ce and Pu system. As displayed in Fig. 3, a similar DT c =Dðc=aÞ 100 are observed in both CeCo1xRhxIn5 and PuCo1xRhxGa5 systems [3]. In the case of Fe and probably also in the case of Ni, the slope strongly increases, evidencing first a non-trivial relation between c/a and Tc and second the influence of the transition metal, although this later is not included in the first coordination sphere of plutonium. The comparison with Pu-substitution by U or Np [5] reveals that in the case of the transition metal substitution this latter has less influence on the critical superconducting parameters, which somewhat confirms that superconductivity in PuCoGa5 is emerging out of electronic states dominated by the Pu 5f electrons.
1083
Acknowledgements We are grateful to J.D. Thompson for fruitful discussions. P.J. acknowledges the European Commission for support in the frame of the ‘‘Training and Mobility of Researchers’’ program.
References [1] J.L. Sarrao, L.A. Morales, J.D. Thompson, B.L. Scott, G.R. Stewart, F. Wastin, J. Rebizant, P. Boulet, E. Colineau, G.H. Lander, Nature (London) 420 (2002) 297. [2] F. Wastin, P. Boulet, J. Rebizant, E. Colineau, G.H. Lander, J. Phys.: Condens. Matter 15 (2003) 2279. [3] J.D. Thompson, J.L. Sarrao, L.A. Morales, F. Wastin, P. Boulet, Physica C 412 (2004) 10. [4] E.D. Bauer, J.D. Thompson, J.L. Sarrao, L.A. Moraloes, F. Wastin, J. Rebizant, et al., Phys. Rev. Lett. 93 (2004) 147005. [5] E. Colineau, F. Wastin, P. Boulet, P. Javorsky, J. Rebizant, this conference, doi:10.1016/j.physb.2005.01.291.