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Anomalous phase transitions in the heavy fermion compound Ce3Ir4Sn13
ARTICLE IN PRESS
Physica B 359–361 (2005) 248–250 www.elsevier.com/locate/physb
Anomalous phase transitions in the heavy fermion compound Ce3Ir4Sn13 C. Nagoshia,, H. Sugawarab, Y. Aokia, S. Sakaia, M. Kohgia, H. Satoa, T. Onimaruc, T. Sakakibarac a
Department of Physics, Faculty of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan b Facility of Integrated Arts and Science, Tokushima University, Tokushima 770-8502, Japan c Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
Abstract We have measured temperature dependence of magnetic susceptibility, resistivity, Hall coefficient, and lattice constant of Ce3 Ir4 Sn13 in order to clarify the origin of anomalies at 0.6 and 2 K in specific heat. The susceptibility measurement indicates that the anomaly at 0.6 K is due to an antiferromagnetic ordering. The Hall coefficient, resistivity, and lattice constant exhibit a sharp change at 2 K, indicating that the transition at 2 K involves a change of the band structure accompanied by a lattice expansion below the transition temperature. r 2005 Published by Elsevier B.V. Keywords: Ce compound; Ce3 Ir4 Sn13 ; Heavy fermion; Antiferromagnetic order; Transport measurement; Crystal field
R3 T4 Sn13 (R: rare earth, T: transition metal) has been extensively studied due to the unique crystal structure and variety of physical properties. This system has a cubic structure with the space group of Pm3n [1], in which R is located in the centre of an icosahedron formed by Sn. For R–R bonding, the nearest-neighbor atoms form one-dimensional chains along x, y, and z directions. The second nearest-neighbor atoms, which connect the chains, form equilateral triangles. Namely this system Corresponding author.
E-mail address: [email protected] (C. Nagoshi). 0921-4526/$ - see front matter r 2005 Published by Elsevier B.V. doi:10.1016/j.physb.2005.01.052
involves one-dimensional and frustrating structures with respect to the magnetic ions. This complex structure may cause various physical phenomena in this system. For Ce3 Ir4 Sn13 ; it was reported that there exist two anomalies at 0.6 and 2 K and also a heavy electron state with the g-value of 670 mJ=K2 mol Ce below 0.6 K [2,3]. To investigate these anomalous properties, we performed magnetic susceptibility, resistivity, Hall effect, and X-ray diffraction measurements by using single crystal samples. Single crystal of Ce3 Ir4 Sn13 were synthesized by Sn flux method. The susceptibility was measured
ARTICLE IN PRESS C. Nagoshi et al. / Physica B 359– 361 (2005) 248–250
0.24 0.22 0.20
30
200 20
1/χ (T Ce-ion /µB)
10
150
0 0
5 10 15 20
100
50
0 0
50
100
150
200
250
300
Temperature (K) Fig. 2. Temperature dependence of 1=w:
6
Hall coefficient (10-9 m3 / C)
by capacitance bridge method (To3 K) and SQUID magnetometer (T43 K) at a magnetic field of 0.1 T along [1 0 0] direction. The Hall coefficient was measured at a magnetic field of 1.5 T along [0 0 1] direction with current along [1 0 0] direction. The temperature dependence of the lattice constant was obtained from the 18 17 0 Bragg peak measured by the Mo-Ka X-ray. The magnetic susceptibility (To3 K) is shown in Fig. 1. The susceptibility shows a peak at 0.6 K and no anomaly at 2 K. The result suggests an antiferromagnetic ordering below 0.6 K, whereas the anomaly at 2 K is non-magnetic. The inverse of susceptibility (T43 K) is shown in Fig. 2. It obeys Curie–Weiss law with effective moment of 2:52 mB per Ce at high temperatures above 50 K. This value is almost the same as one of a free Ce3þ ion: 2:54 mB : Since the susceptibility supports the localized nature of the 4f-electron state, it was analyzed on the basis of the crystal field model, where the Hamiltonian is assumed to be H ¼ B02 O02 þ B04 O04 þ B44 O44 considering the tetragonal site symmetry. The solid line in Fig. 2 is the best fit of the calculated inverse susceptibility. The obtained parameters are B02 ¼ 0:0447; B04 ¼ 0:407; B44 ¼ 0:176; which give the crystal field splitting of D1 ¼ 20 K and D2 ¼ 250 K for three doublets. The D2 value is consistent with a small hump of resistivity around 60 K [2].
249
4
2
0
-2
χ (µB /Ce-ion T)
0.18 0.16
4
6 8
2
1
0.14
4
6 8
2
10 Temperature (K)
4
6 8
2
100
0.12 Fig. 3. Temperature dependence of Hall coefficient.
0.10 0.08 0.06 0.04 0.02 0.00 0.5
1.0
1.5 2.0 Temperature (K)
Fig. 1. M–T curve.
2.5
3.0
The Hall coefficient, shown in Fig. 3, increases with decreasing temperature, and shows a sudden drop below 2 K. It does not show any anomaly at 0.6 K. This result is in contrast to the case of the susceptibility, where anomaly is seen only at 0.6 K. Similar drop is also observed in the resistivity
ARTICLE IN PRESS C. Nagoshi et al. / Physica B 359– 361 (2005) 248–250
250
9.704
9.720 9.703
Lattice constant (A)
9.702 9.701
9.715
9.700 9.699 0
9.710
2
4
6
8 10
9.705
9.700 0
50
100
150
200
250
300
Temperature (K) Fig. 4. Temperature dependence of lattice constant.
below 2 K (not shown in this paper). This fact strongly suggests that the phase transition at 2 K involves the change of the band structure of the compound. The negative slope of the Hall coefficient above 2 K may correspond to the
Kondo-like negative slope of the resistivity observed in the same temperature range [2]. The temperature dependence of the lattice constant is shown in Fig. 4. The lattice constant increases suddenly below 2 K, indicating that the phase transition at 2 K is accompanied by a structural change. The compound shows super lattice reflections characterized by the wave vector q ¼ ð1=2 1=2 0Þ from 1 to 300 K. However, no additional superlattice reflection was found below 2 K. From our experimental results it is concluded that the phase transition at 0.6 K will be antiferromagnetic one, whereas the transition at 2 K is non-magnetic one involving a change of the band structure accompanied by a lattice expansion. Since the entropy of the compound at 4 K is reported to be only 0.6 ln 2 [3], there is a strong suppression of the entropy of the grand doublet even at 4 K. References [1] J.L. Hondeau, et al., Solid State Commun. 42 (1982) 97. [2] H. Sato, et al., Physica B 186–188 (1993) 630. [3] S. Takayanagi, et al., Physica B 199–200 (1994) 49.
Physica B 359–361 (2005) 248–250 www.elsevier.com/locate/physb
Anomalous phase transitions in the heavy fermion compound Ce3Ir4Sn13 C. Nagoshia,, H. Sugawarab, Y. Aokia, S. Sakaia, M. Kohgia, H. Satoa, T. Onimaruc, T. Sakakibarac a
Department of Physics, Faculty of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan b Facility of Integrated Arts and Science, Tokushima University, Tokushima 770-8502, Japan c Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
Abstract We have measured temperature dependence of magnetic susceptibility, resistivity, Hall coefficient, and lattice constant of Ce3 Ir4 Sn13 in order to clarify the origin of anomalies at 0.6 and 2 K in specific heat. The susceptibility measurement indicates that the anomaly at 0.6 K is due to an antiferromagnetic ordering. The Hall coefficient, resistivity, and lattice constant exhibit a sharp change at 2 K, indicating that the transition at 2 K involves a change of the band structure accompanied by a lattice expansion below the transition temperature. r 2005 Published by Elsevier B.V. Keywords: Ce compound; Ce3 Ir4 Sn13 ; Heavy fermion; Antiferromagnetic order; Transport measurement; Crystal field
R3 T4 Sn13 (R: rare earth, T: transition metal) has been extensively studied due to the unique crystal structure and variety of physical properties. This system has a cubic structure with the space group of Pm3n [1], in which R is located in the centre of an icosahedron formed by Sn. For R–R bonding, the nearest-neighbor atoms form one-dimensional chains along x, y, and z directions. The second nearest-neighbor atoms, which connect the chains, form equilateral triangles. Namely this system Corresponding author.
E-mail address: [email protected] (C. Nagoshi). 0921-4526/$ - see front matter r 2005 Published by Elsevier B.V. doi:10.1016/j.physb.2005.01.052
involves one-dimensional and frustrating structures with respect to the magnetic ions. This complex structure may cause various physical phenomena in this system. For Ce3 Ir4 Sn13 ; it was reported that there exist two anomalies at 0.6 and 2 K and also a heavy electron state with the g-value of 670 mJ=K2 mol Ce below 0.6 K [2,3]. To investigate these anomalous properties, we performed magnetic susceptibility, resistivity, Hall effect, and X-ray diffraction measurements by using single crystal samples. Single crystal of Ce3 Ir4 Sn13 were synthesized by Sn flux method. The susceptibility was measured
ARTICLE IN PRESS C. Nagoshi et al. / Physica B 359– 361 (2005) 248–250
0.24 0.22 0.20
30
200 20
1/χ (T Ce-ion /µB)
10
150
0 0
5 10 15 20
100
50
0 0
50
100
150
200
250
300
Temperature (K) Fig. 2. Temperature dependence of 1=w:
6
Hall coefficient (10-9 m3 / C)
by capacitance bridge method (To3 K) and SQUID magnetometer (T43 K) at a magnetic field of 0.1 T along [1 0 0] direction. The Hall coefficient was measured at a magnetic field of 1.5 T along [0 0 1] direction with current along [1 0 0] direction. The temperature dependence of the lattice constant was obtained from the 18 17 0 Bragg peak measured by the Mo-Ka X-ray. The magnetic susceptibility (To3 K) is shown in Fig. 1. The susceptibility shows a peak at 0.6 K and no anomaly at 2 K. The result suggests an antiferromagnetic ordering below 0.6 K, whereas the anomaly at 2 K is non-magnetic. The inverse of susceptibility (T43 K) is shown in Fig. 2. It obeys Curie–Weiss law with effective moment of 2:52 mB per Ce at high temperatures above 50 K. This value is almost the same as one of a free Ce3þ ion: 2:54 mB : Since the susceptibility supports the localized nature of the 4f-electron state, it was analyzed on the basis of the crystal field model, where the Hamiltonian is assumed to be H ¼ B02 O02 þ B04 O04 þ B44 O44 considering the tetragonal site symmetry. The solid line in Fig. 2 is the best fit of the calculated inverse susceptibility. The obtained parameters are B02 ¼ 0:0447; B04 ¼ 0:407; B44 ¼ 0:176; which give the crystal field splitting of D1 ¼ 20 K and D2 ¼ 250 K for three doublets. The D2 value is consistent with a small hump of resistivity around 60 K [2].
249
4
2
0
-2
χ (µB /Ce-ion T)
0.18 0.16
4
6 8
2
1
0.14
4
6 8
2
10 Temperature (K)
4
6 8
2
100
0.12 Fig. 3. Temperature dependence of Hall coefficient.
0.10 0.08 0.06 0.04 0.02 0.00 0.5
1.0
1.5 2.0 Temperature (K)
Fig. 1. M–T curve.
2.5
3.0
The Hall coefficient, shown in Fig. 3, increases with decreasing temperature, and shows a sudden drop below 2 K. It does not show any anomaly at 0.6 K. This result is in contrast to the case of the susceptibility, where anomaly is seen only at 0.6 K. Similar drop is also observed in the resistivity
ARTICLE IN PRESS C. Nagoshi et al. / Physica B 359– 361 (2005) 248–250
250
9.704
9.720 9.703
Lattice constant (A)
9.702 9.701
9.715
9.700 9.699 0
9.710
2
4
6
8 10
9.705
9.700 0
50
100
150
200
250
300
Temperature (K) Fig. 4. Temperature dependence of lattice constant.
below 2 K (not shown in this paper). This fact strongly suggests that the phase transition at 2 K involves the change of the band structure of the compound. The negative slope of the Hall coefficient above 2 K may correspond to the
Kondo-like negative slope of the resistivity observed in the same temperature range [2]. The temperature dependence of the lattice constant is shown in Fig. 4. The lattice constant increases suddenly below 2 K, indicating that the phase transition at 2 K is accompanied by a structural change. The compound shows super lattice reflections characterized by the wave vector q ¼ ð1=2 1=2 0Þ from 1 to 300 K. However, no additional superlattice reflection was found below 2 K. From our experimental results it is concluded that the phase transition at 0.6 K will be antiferromagnetic one, whereas the transition at 2 K is non-magnetic one involving a change of the band structure accompanied by a lattice expansion. Since the entropy of the compound at 4 K is reported to be only 0.6 ln 2 [3], there is a strong suppression of the entropy of the grand doublet even at 4 K. References [1] J.L. Hondeau, et al., Solid State Commun. 42 (1982) 97. [2] H. Sato, et al., Physica B 186–188 (1993) 630. [3] S. Takayanagi, et al., Physica B 199–200 (1994) 49.