- Email: [email protected]
Magnetic properties of Ce2CuIn3
ARTICLE IN PRESS
Physica B 378–380 (2006) 847–848 www.elsevier.com/locate/physb
Magnetic properties of Ce2 CuIn3 D.P. Rojas, J.I. Espeso, J. Rodrı´ guez Ferna´ndez, J.C. Gomez Sal DCITIMAC, University of Cantabria, 39005 Santander, Spain
Abstract We report measurements on magnetic properties of Ce2 CuIn3 compound. Irreversibility of the ZFC–FC curves of the DC magnetic susceptibility (M/H) at low field, and the shift of the peak with the frequency in the AC susceptibility give evidences for spin glass (SG) behavior at freezing temperature of T f ¼ 2:1 K. In addition, the relative shift per frequency decade, DT f =T f D log n ¼ 0:016, is similar to those reported for other spin glasses. We discuss the results in relation with the other isotypic, Ce2 TX3 (T ¼ Transition metal and X ¼ Si, Ge and In). The interplay of disorder and frustration within hexagonal CaIn2 type of structure and competition between RKKY interaction and Kondo effect are suggested as the main causes for the arising magnetic ground state. r 2006 Elsevier B.V. All rights reserved. PACS: 71.27.+a; 75.30.Mb Keywords: Ce2 CuIn3 ; AC susceptibility; Spin glass
Most of the compounds of the type Ce2 TX3 , where T ¼ Transition metal and X ¼ Si, Ge, In, have been classified as non-magnetic atom disorder (NMAD) spin glasses [1–4]. In this kind of intermetallics, the disorder and frustration come from the statistical distribution of T and X atoms on a crystallographic site of the AlB2 (or derived) hexagonal type of structure. As a result, a random Ce–Ce exchange interaction gives way to the emerging magnetic ground state. Inside this large family of compounds, Ce2 CuIn3 has been reported to crystallize in the AlB2 type of structure and remains paramagnetic down to 4.2 K [1]. Thus, in the present work we pretend a more detailed study of its physical properties. The sample was prepared in an arc melting furnace from the stoichiometric amounts of constituent materials Ce (3N), Cu (5N), In (4N) (Johnson Matthey) with subsequent annealing at 750 C for seven days. The analysis of the X-ray diffraction data reveals a single phase sample with the hexagonal CaIn2 type of structure (space group P63 =mmc), ˚ c ¼ 7:680ð1Þ A. ˚ Other and with parameters: a ¼ 4:822ð1Þ A; isotypics like Ce2 CuGa3 and Ce2 AgIn3 have also been found Corresponding author. Tel.: +34 942 201512.
E-mail address: [email protected] (D.P. Rojas). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.01.312
to present the same type of structure [4,5]. In spite of our result being different to that reported for Ce2 CuIn3 [1], it is worth to noticing that the CaIn2 type of structure is derived from the hexagonal AlB2 (space group P6/mmm) for a small displacement of the B atoms from the 2d position leading to the double ‘‘c’’ parameter. So, the crystallographic properties of Ce2 CuIn3 may rely on the conditions of preparation of this material. Measurements of the magnetic properties were carried out in a Quantum Design SQUID magnetometer in the temperature range between 1.8 and 300 K. In Fig. 1, the temperature dependence of the in-phase component of the zero field AC susceptibility for frequencies ranging from 1 Hz to 1 kHz is presented. The typical feature of a spin glass behavior is observed by the shift of the peak with the frequency. The freezing temperature of T f ¼ 2:1 K can be defined from the peak at the lowest measured frequency of 1 Hz. In addition, the value of the relative shift per frequency decade, DT f =T f D log n ¼ 0:016, is similar to those reported for other NMAD spin glasses [2–4]. In the inset, the zero field cooled (ZFC) and field cooled (FC) curves of the DC magnetic susceptibility (M/H) for the magnetic field of 20 Oe are depicted. Some irreversibility of the curves, and a maximum appearing in the ZFC curve at the freezing temperature of T f ¼ 2:1 K, also supports a SG
ARTICLE IN PRESS D.P. Rojas et al. / Physica B 378–380 (2006) 847–848
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behavior. The analysis of the data for temperatures above 100 K gives a Curie–Weiss dependence with a paramagnetic Curie temperature of yp ¼ 12 K and an effective magnetic moment of meff ¼ 2:59 mB , close to the value for the Ce3þ free ion ð2:54 mB ). The study of the relaxation processes is important for the characterization of the systems as SG. In the measurement of the isothermal remanent magnetization (IRM), the sample was ZFC from temperatures higher than T f down to 1.8 K; then, a magnetic field of 5 kOe was applied during 5 min. Afterwards, the field was removed and the magnetization data as function of time were collected. The result is shown in Fig. 2a. There is a region with log T dependence characteristic of SG behavior. A deviation from log T dependence for shorter times of measurement has also been observed in other NMAD spin glasses, and has been considered using an extra exponential term. Fig. 2b displays the magnetic field dependence of the isothermal magnetization at T ¼ 1:8 K up to 50 kOe. The saturation is not achieved for the highest field of our measurement and the magnetization reaches a value near to 1mB =molCe, much smaller than the expected one for Ce3þ ð2:14 mB =molCeÞ. It could be associated to the Kondo effect. In the inset the low field region is plotted. It shows the feature of linear dependence of the SG behavior up to 500 Oe approximately. From this value the magnetic energy of Ce3þ ions ðmeff HÞ seems to prevail over the thermal disorder energy ðkB T f Þ [3]. Summarizing, our magnetic results suggest a SG behavior for the title intermetallic. Other isotypic systems like Ce2 CuSi3 ðT f ¼ 2:7 KÞ and Ce2 CuGe3 ðT f ¼ 3:0 KÞ have also shown SG characteristics [2,3]. However, these systems crystallize in a different type of structure: orthorhombic for the last and hexagonal AlB2 for the
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10
20
30
40
50
H(kOe)
Fig. 2. (a) IRM at T ¼ 1:8 K as function of time with log T dependence. (b) Isothermal magnetization at T ¼ 1:8 K vs magnetic field. Details of low temperature region are shown in the inset.
former. Hence, it is better to compare our results with those reported for the Ce2 AgIn3 (CaIn2 type and a ¼ ˚ c ¼ 7:647 AÞ ˚ [4]. For this last compound a SG 4:904 A; behavior was observed at T f ¼ 1:86 K, near to the freezing temperature of T f ¼ 2:1 K for the Cu compound. So, the changes in the unit cell volume ð3%Þ seems not to modify significantly the relative strength between RKKY interaction and Kondo effect. However, we believe that besides the frustration introduced by the disorder within hexagonal CaIn2 type of structure, the competition between RKKY interaction and Kondo effect may have significant influence in the formation of the magnetic ground state in these systems. Further, study on thermodynamic and electronic transport properties is necessary in order to elucidate the role of the magnetic interactions and disorder on the SG behavior of this material. This work was supported by the Direction of the Universities of the Ministry of Science and Education of Spain under contracts MAT 2003-06815 and SB2003-0102.
References [1] [2] [3] [4] [5]
I.M. Siouris, et al., J. Alloys Compd. 297 (2000) 26. D.X. Li, et al., Physica B 329–333 (2003) 506. C. Tien, et al., Phys. Rev. B 61 (2000) 12151. T. Nishioka, et al., J. Phys. Soc. Japan 69 (2000) 1012. V.Ja. Markiv, Dopov. Akad. Nauk Ukr. RSR, Ser. A 44 (1982) 84.
Physica B 378–380 (2006) 847–848 www.elsevier.com/locate/physb
Magnetic properties of Ce2 CuIn3 D.P. Rojas, J.I. Espeso, J. Rodrı´ guez Ferna´ndez, J.C. Gomez Sal DCITIMAC, University of Cantabria, 39005 Santander, Spain
Abstract We report measurements on magnetic properties of Ce2 CuIn3 compound. Irreversibility of the ZFC–FC curves of the DC magnetic susceptibility (M/H) at low field, and the shift of the peak with the frequency in the AC susceptibility give evidences for spin glass (SG) behavior at freezing temperature of T f ¼ 2:1 K. In addition, the relative shift per frequency decade, DT f =T f D log n ¼ 0:016, is similar to those reported for other spin glasses. We discuss the results in relation with the other isotypic, Ce2 TX3 (T ¼ Transition metal and X ¼ Si, Ge and In). The interplay of disorder and frustration within hexagonal CaIn2 type of structure and competition between RKKY interaction and Kondo effect are suggested as the main causes for the arising magnetic ground state. r 2006 Elsevier B.V. All rights reserved. PACS: 71.27.+a; 75.30.Mb Keywords: Ce2 CuIn3 ; AC susceptibility; Spin glass
Most of the compounds of the type Ce2 TX3 , where T ¼ Transition metal and X ¼ Si, Ge, In, have been classified as non-magnetic atom disorder (NMAD) spin glasses [1–4]. In this kind of intermetallics, the disorder and frustration come from the statistical distribution of T and X atoms on a crystallographic site of the AlB2 (or derived) hexagonal type of structure. As a result, a random Ce–Ce exchange interaction gives way to the emerging magnetic ground state. Inside this large family of compounds, Ce2 CuIn3 has been reported to crystallize in the AlB2 type of structure and remains paramagnetic down to 4.2 K [1]. Thus, in the present work we pretend a more detailed study of its physical properties. The sample was prepared in an arc melting furnace from the stoichiometric amounts of constituent materials Ce (3N), Cu (5N), In (4N) (Johnson Matthey) with subsequent annealing at 750 C for seven days. The analysis of the X-ray diffraction data reveals a single phase sample with the hexagonal CaIn2 type of structure (space group P63 =mmc), ˚ c ¼ 7:680ð1Þ A. ˚ Other and with parameters: a ¼ 4:822ð1Þ A; isotypics like Ce2 CuGa3 and Ce2 AgIn3 have also been found Corresponding author. Tel.: +34 942 201512.
E-mail address: [email protected] (D.P. Rojas). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.01.312
to present the same type of structure [4,5]. In spite of our result being different to that reported for Ce2 CuIn3 [1], it is worth to noticing that the CaIn2 type of structure is derived from the hexagonal AlB2 (space group P6/mmm) for a small displacement of the B atoms from the 2d position leading to the double ‘‘c’’ parameter. So, the crystallographic properties of Ce2 CuIn3 may rely on the conditions of preparation of this material. Measurements of the magnetic properties were carried out in a Quantum Design SQUID magnetometer in the temperature range between 1.8 and 300 K. In Fig. 1, the temperature dependence of the in-phase component of the zero field AC susceptibility for frequencies ranging from 1 Hz to 1 kHz is presented. The typical feature of a spin glass behavior is observed by the shift of the peak with the frequency. The freezing temperature of T f ¼ 2:1 K can be defined from the peak at the lowest measured frequency of 1 Hz. In addition, the value of the relative shift per frequency decade, DT f =T f D log n ¼ 0:016, is similar to those reported for other NMAD spin glasses [2–4]. In the inset, the zero field cooled (ZFC) and field cooled (FC) curves of the DC magnetic susceptibility (M/H) for the magnetic field of 20 Oe are depicted. Some irreversibility of the curves, and a maximum appearing in the ZFC curve at the freezing temperature of T f ¼ 2:1 K, also supports a SG
ARTICLE IN PRESS D.P. Rojas et al. / Physica B 378–380 (2006) 847–848
848
1.0
χ′(emu/g.10-3)
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0.15
H=20 Oe
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M(emu/g.10-3)
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behavior. The analysis of the data for temperatures above 100 K gives a Curie–Weiss dependence with a paramagnetic Curie temperature of yp ¼ 12 K and an effective magnetic moment of meff ¼ 2:59 mB , close to the value for the Ce3þ free ion ð2:54 mB ). The study of the relaxation processes is important for the characterization of the systems as SG. In the measurement of the isothermal remanent magnetization (IRM), the sample was ZFC from temperatures higher than T f down to 1.8 K; then, a magnetic field of 5 kOe was applied during 5 min. Afterwards, the field was removed and the magnetization data as function of time were collected. The result is shown in Fig. 2a. There is a region with log T dependence characteristic of SG behavior. A deviation from log T dependence for shorter times of measurement has also been observed in other NMAD spin glasses, and has been considered using an extra exponential term. Fig. 2b displays the magnetic field dependence of the isothermal magnetization at T ¼ 1:8 K up to 50 kOe. The saturation is not achieved for the highest field of our measurement and the magnetization reaches a value near to 1mB =molCe, much smaller than the expected one for Ce3þ ð2:14 mB =molCeÞ. It could be associated to the Kondo effect. In the inset the low field region is plotted. It shows the feature of linear dependence of the SG behavior up to 500 Oe approximately. From this value the magnetic energy of Ce3þ ions ðmeff HÞ seems to prevail over the thermal disorder energy ðkB T f Þ [3]. Summarizing, our magnetic results suggest a SG behavior for the title intermetallic. Other isotypic systems like Ce2 CuSi3 ðT f ¼ 2:7 KÞ and Ce2 CuGe3 ðT f ¼ 3:0 KÞ have also shown SG characteristics [2,3]. However, these systems crystallize in a different type of structure: orthorhombic for the last and hexagonal AlB2 for the
0.06
(b)
10
20
30
40
50
H(kOe)
Fig. 2. (a) IRM at T ¼ 1:8 K as function of time with log T dependence. (b) Isothermal magnetization at T ¼ 1:8 K vs magnetic field. Details of low temperature region are shown in the inset.
former. Hence, it is better to compare our results with those reported for the Ce2 AgIn3 (CaIn2 type and a ¼ ˚ c ¼ 7:647 AÞ ˚ [4]. For this last compound a SG 4:904 A; behavior was observed at T f ¼ 1:86 K, near to the freezing temperature of T f ¼ 2:1 K for the Cu compound. So, the changes in the unit cell volume ð3%Þ seems not to modify significantly the relative strength between RKKY interaction and Kondo effect. However, we believe that besides the frustration introduced by the disorder within hexagonal CaIn2 type of structure, the competition between RKKY interaction and Kondo effect may have significant influence in the formation of the magnetic ground state in these systems. Further, study on thermodynamic and electronic transport properties is necessary in order to elucidate the role of the magnetic interactions and disorder on the SG behavior of this material. This work was supported by the Direction of the Universities of the Ministry of Science and Education of Spain under contracts MAT 2003-06815 and SB2003-0102.
References [1] [2] [3] [4] [5]
I.M. Siouris, et al., J. Alloys Compd. 297 (2000) 26. D.X. Li, et al., Physica B 329–333 (2003) 506. C. Tien, et al., Phys. Rev. B 61 (2000) 12151. T. Nishioka, et al., J. Phys. Soc. Japan 69 (2000) 1012. V.Ja. Markiv, Dopov. Akad. Nauk Ukr. RSR, Ser. A 44 (1982) 84.