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Magnetic behavior in CeT0.6Ga6 (T=Ni and Cu) compounds
Solid State Communications 122 (2002) 637–640 www.elsevier.com/locate/ssc
Magnetic behavior in CeT0.6Ga6 (T ¼ Ni and Cu) compounds D. Kaczorowskia,*, Yu. Grinb a
Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Oko´lna 2, 50-950 Wrocław, Poland b Max-Planck-Institut fu¨r Chemische Physik fester Stoffe, No¨thnitzer Str. 40, 01187 Dresden, Germany
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Received 14 March 2002; accepted 21 May 2002 by E. Molinari
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Abstract
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The ternary gallides CeNi0.6Ga6 and CeCu0.6Ga6 were prepared by induction melting and studied by means of SQUID and resistivity measurements. Both compounds exhibit well-localized magnetism due to the presence of trivalent Ce ions. The nickel-based compound orders antiferromagnetically at TN ¼ 10 K; whereas that containing copper remains paramagnetic down to 2 K. The electrical resistivity of CeNi0.6Ga6 has a metallic character and shows pronounced crystal field effects at low temperatures. q 2002 Elsevier Science Ltd. All rights reserved. PACS: 75.30.Mb; 72.15.Eb; 72.15.Qm
1. Introduction
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Ternary cerium-based intermetallics continue to attract much experimental interest owing to a large variety in their physical properties, which span from valence fluctuations, through Kondo effect and heavy fermion behavior, up to well-localized magnetism with long-range magnetic order. Search for new ternaries sometimes results in eminent discoveries, like recent finding of pressure-induced superconductivity in antiferromagnetic heavy-fermion material CeRhIn5 [1], and ambient-pressure heavy-fermion superconductivity in isostructural paramagnetic compounds CeCoIn5 [2] and CeIrIn5 [3]. The systems Ce – Ni – Ga and Ce – Cu – Ga comprise several ternary phases [4] but only very few of them have been characterized with respect to their magnetic behavior. Relatively well studied have been antiferromagnetically ordered Kondo lattices CeCuGa [5] and CeCuGa3 [6], as well as the alloy series Ce(Ni,Ga)4, which exhibits the interplay of Kondo effect and ferromagnetism [7 – 9]. Recently we reported on intermediate valent character of Ce2Ni2Ga [10] and the coexistence of Kondo interactions and antiferromagnetism in CeNiGa2 [10,11]. The latter
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Keywords: A. Intermetallic compounds; A. Magnetically ordered materials; D. Magnetic properties; D. Electronic transport
* Corresponding author. Tel.: þ48-71-34-350-21; fax: þ 48-7134-410-29. E-mail address: [email protected] (D. Kaczorowski).
gallide focused particular attention due to its suitability for a study of non-Fermi-liquid state that develops in this stoichiometric, crystallographically well-ordered compound upon suppression of the long-range magnetic ordering by external pressure of only 4 kbar [12,13]. The two compounds investigated in the present work, CeNi0.6Ga6 and CeCu0.6Ga6, were reported for the first time in eighties [4,14], yet to our knowledge no physical data are available in the literature till date. Both crystallize in a tetragonal system, space group P4/mmm, but with different structure types, closely related to one another. In this paper we report on the magnetic properties of both materials and the electrical resistivity of CeNi0.6Ga6.
2. Experimental Polycrystalline samples of CeNi0.6Ga6 and CeCu0.6Ga6 were prepared by melting appropriate amounts of the constituting elements (Ce: 99.95% Ames Lab.; Ni: 99.99%, Chempur; Cu: 99.99%, Heraeus; Ga: 99.999% Chempur) in carbon-glass crucibles using an induction furnace installed in an argon glove box. The buttons were turned over and remelted several times to ensure good homogeneity. The weight losses after melting were below 0.2%. Subsequently the specimens were wrapped with
0038-1098/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 8 - 1 0 9 8 ( 0 2 ) 0 0 2 2 2 - 3
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D. Kaczorowski, Y. Grin / Solid State Communications 122 (2002) 637–640
3. Results and discussion
Fig. 1. Crystal structures of CeNi0.6Ga6 and CeCu0.6Ga6 (upper part) and the two possible variants of the environment for cerium atoms (lower part).
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The metallographic investigation of the sample with nominal composition CeCu0.6Ga6 revealed the single phase material. The EDX analysis yielded the exact composition CeCu0.63(1)Ga6.03(3) being in good agreement with the literature data [4]. The X-ray powder diffraction patterns of CeNi0.6Ga6 and CeCu0.6Ga6 were easily indexed in a primitive tetragonal system with the lattice parameters: a ¼ 426:86ð4Þ pm and c ¼ 1549:59ð8Þ pm for the Ni-containing compound, and a ¼ 431:65ð2Þ pm and c ¼ 768:29ð5Þ pm for the copper one. These values are similar to those reported in the literature [4,14]. No significant foreign lines were observed on both diffractograms, in agreement with the metallographical results. Moreover, the measured X-ray intensities agreed well with the calculated ones, which were obtained assuming the atomic parameters for CeCu0.6Ga6 as given in Ref. [2], and those for CeNi0.6Ga6 as determined in Ref. [14] for the prototype structure of LaNi0.6Ga6. The unit cells of both compounds are shown in the upper part of Fig. 1. The two structures differ in the occupation of the transition metal positions. In CeCu0.6Ga6, the copper atoms are located at a single site with the occupancy of 60%. In turn, there are two positions of the nickel atoms in CeNi0.6Ga6. One of them (Ni1) is fully occupied, and the other one (Ni2) has the occupancy of 20%. The environment of the cerium atoms is consequently quite similar: the first coordination shell consists of 14 gallium atoms (see lower part of Fig. 1). The notable differences occur only in the second coordination shell: (i) the distance between cerium atoms in CeCu0.6Ga6 is larger than that in CeNi0.6Ga6 (d(Ce –Ce) ¼ 432 and 427 pm, respectively); (ii) depending
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molybdenum foil, placed in quartz tubes and annealed in vacuum at 400 8C for 1 month. Quality of the annealed samples were checked by metallographical analysis. The specimen cuts were polished with several diamond-powder-containing polishing fluids. Photographs were taken with a CCD camera on a Zeiss Axioplan 2 optical microscope. Composition of the phases was determined by EDX method using a Phillips CM20 scanning electron microscope. The prepared alloys were additionally investigated by X-ray powder diffraction using a Guinier Huber G670 camera with Cu Ka1 radiation and germanium as an internal standard. The X-ray patterns were evaluated by means of the STOE WinXPOW program package. The structural data were taken from Ref. [4]. Magnetic measurements were carried out in the temperature range 2 – 400 K and in applied magnetic fields up to 5 T using a Quantum Design MPMS-5 SQUID magnetometer. The electrical resistivity was measured over the temperature interval 4.2 –300 K employing a conventional four-point dc technique.
on the local ordering, each cerium atom can have one (see bottom left part of Fig. 1) or two (see bottom right part of Fig. 1) neighboring transition metal atoms, being in the latter case equidistant to the central Ce-atom in CeCu0.6Ga6 (d1(Ce – TM) ¼ d2(Ce – TM) ¼ 384 pm) but having two distinct distances to the Ce-atom in CeNi0.6Ga6 (d1(Ce– TM) ¼ 382 pm and d2(Ce– TM) ¼ 393 pm). The temperature variation of the magnetic susceptibility of CeNi0.6Ga6 is given in Fig. 2. Above 100 K, x 21(T ) follows a Curie– Weiss law with the effective magnetic moment of 2.43(2)mB per formula unit and the paramagnetic Curie temperature close to zero. The experimental meff value is somewhat reduced with respect to that expected for a free Ce3þ ion (2.54mB). At lower temperatures x 21(T ) slightly deviates from a straight line, presumably due to thermal depopulation of crystal field energy levels. As emphasized in upper inset to Fig. 2, at TN ¼ 10ð1Þ K the compound orders antiferromagnetically. The antiferromagnetic nature of this phase transition is corroborated by a characteristic metamagnetic behavior of the magnetization, measured at T ¼ 2 K as a function of magnetic field (see lower inset to Fig. 2). The salient metamagnetic transition occurs in CeNi0.6Ga6 at the critical field Bc ¼ 3 T: The electrical resistivity of CeNi0.6Ga6 (see Fig. 3)
D. Kaczorowski, Y. Grin / Solid State Communications 122 (2002) 637–640
Fig. 2. Temperature dependence of the inverse molar magnetic susceptibility of CeNi0.6Ga6 measured in a field of 0.1 T. The solid line represents a Curie–Weiss fit of the experimental data with the parameters given in the text. The upper inset displays the low temperature susceptibility. The arrow marks the antiferromagnetic phase transition at TN ¼ 10 K: The lower inset presents the field variation of the magnetization in CeNi0.6Ga6, taken at T ¼ 2 K with increasing (full circles) and decreasing (open circles) magnetic field. The dashed line indicates a linear behavior of s(B ) below the metamagnetic transition at Bc ¼ 3 T:
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Fig. 4. Temperature dependence of the inverse molar magnetic susceptibility of CeCu0.6Ga6 measured in a field of 0.5 T. The solid line represents a Curie–Weiss fit of the experimental data with the parameters given in the text. The upper inset displays the low temperature susceptibility. The lower inset presents the field variation of the magnetization in CeCu0.6Ga6, taken at T ¼ 2 K with increasing (full circles) and decreasing (open circles) magnetic field.
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Contrary to its Ni-containing analogue, the CeCu0.6Ga6 compound does not order magnetically down to 2 K. The reciprocal magnetic susceptibility of this compound, given in Fig. 4, exhibits a linear behavior at temperatures above 100 K, yielding the Curie – Weiss parameters: meff ¼ 2:53ð5ÞmB and up ¼ 11ð2Þ K: This effective magnetic moment is nearly equal to the Hund’s rule value for trivalent Ce ion. The positive and relatively high paramagnetic Curie temperature might evidence the presence of magnetic exchange interactions of ferromagnetic character, yet no magnetic ordering is observed in x(T ) at low temperatures (see upper inset to Fig. 4). Similarly to CeNi0.6Ga6, the deviation of the susceptibility from a Curie– Weiss law, observed at low temperatures, presumably results from crystal field interactions. Apparently, also the s(B ) variation taken at T ¼ 2 K exhibits a paramagnetic behavior (see lower inset to Fig. 4), although its strong curvature may hint on magnetic order setting at somewhat lower temperature.
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diminishes almost linearly with decreasing temperature from 290 down to 60 K, and then falls down more rapidly. The curvature of r(T ) in this region results probably from crystal field effects being consistent with the magnetic susceptibility behavior. The antiferromagnetic phase transition at TN ¼ 10 K manifests itself as a distinct kink in the r(T ) curve and as a Fisher – Langer-type anomaly in the temperature dependence of the resistivity derivative (see inset to Fig. 3). Below TN the resistivity keeps declining, most likely mainly due to continuous decrease towards lower temperatures in both spin-disorder and phonon scattering of conduction electrons.
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4. Conclusions The two cerium compounds investigated in this work reveal well-localized magnetism due to the presence of Ce3þ ions. CeNi0.6Ga6 becomes antiferromagnetic below TN ¼ 10 K and exhibits pronounced metamagnetic properties with a critical field of 3 T at 2 K. In contrast, CeCu0.6Ga6 remains paramagnetic down to 2 K. This difference in the magnetic behavior of these two structurally very closely related compounds may be attributed to dissimilar effectiveness of magnetic exchange interactions
D. Kaczorowski, Y. Grin / Solid State Communications 122 (2002) 637–640
Acknowledgments
References
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[1] H. Hegger, C. Petrovic, E.G. Moshopoulou, M.F. Hundley, J.L. Sarrao, Z. Fisk, J.D. Thompson, Phys. Rev. Lett. 84 (2000) 4986.
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DK is grateful to the Max Planck Society for the Advancement of Science for a fellowship. The authors thank Mrs M. Eckert for metallographical studies.
[2] C. Petrovic, P.G. Pagliuso, M.F. Hundley, R. Movshovich, J.L. Sarrao, J.D. Thompson, Z. Fisk, P. Monthoux, J. Phys.: Condens. Matter 13 (2001) L337. [3] C. Petrovic, R. Movshovich, M. Jaime, P.G. Pagliuso, M.F. Hundley, J.L. Sarrao, Z. Fisk, J.D. Thompson, Europhys. Lett. 53 (2001) 354. [4] Yu.N. Grin, Gallides, Metallurgia, Moscow, 1989, in Russian. [5] H. Nakotte, E. Bruck, K. Prokes, F.R. de Boer, J. Kuang, H. Cui, J. Li, F. Yang, IEEE Trans. Magn. 30 (1994) 1202. [6] J.M. Martin, D.M. Paul, M.R. Lees, D. Werner, E. Bauer, J. Magn. Magn. Mater. 159 (1996) 223. [7] Yu.N. Grin, P. Rogl, H. Noe¨l, J. Less-Common Met. 162 (1990) 361. [8] Yu.N. Grin, K. Hiebl, P. Rogl, H. Noe¨l, J. Less-Common Met. 162 (1990) 371. [9] E.V. Sampathkumaran, K. Hirota, I. Das, M. Ishikawa, Phys. Rev. B 47 (1993) 8349. [10] D. Kaczorowski, P. Rogl, Acta Phys. Pol., A 92 (1997) 289. [11] M.D. Koterlin, B.S. Morokhivskii, Yu.N. Grin, Soy. Phys. Solid State 30 (1988) 517. [12] R. Hauser, E. Bauer, G. Hilscher, H. Michor, D. Kaczorowski, Physica B 237–238 (1997) 205. [13] R. Hauser, E. Bauer, A. Kottar, G. Hilscher, D. Kaczorowski, M. Galli, J. Magn. Magn. Mater. 177–181 (1998) 292. [14] Yu.N. Grin, P. Yarmolyuk, I.V. Rozhdestvenskaya, E.I. Gladyshevshii, Soy. Phys. Crystallogr. 27 (1982) 693.
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between Ce atoms (because of the differences in the Ce – Ce interatomic distances as well as in the local arrangement of the transition metal atoms in the second coordination sphere of the cerium atoms) and/or various magnitude of hybridization between conduction- and 4f-electronic states (because of different electron contribution from copper and nickel). In numerous cerium intermetallics the latter mechanism brings about development of Kondo features in the electronic transport properties. The electrical conductivity of CeNi0.6Ga6 has a metallic character but on the basis of its temperature dependence no straightforward conclusion about Kondo effect can be formulated.
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Magnetic behavior in CeT0.6Ga6 (T ¼ Ni and Cu) compounds D. Kaczorowskia,*, Yu. Grinb a
Institute for Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Oko´lna 2, 50-950 Wrocław, Poland b Max-Planck-Institut fu¨r Chemische Physik fester Stoffe, No¨thnitzer Str. 40, 01187 Dresden, Germany
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Received 14 March 2002; accepted 21 May 2002 by E. Molinari
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Abstract
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The ternary gallides CeNi0.6Ga6 and CeCu0.6Ga6 were prepared by induction melting and studied by means of SQUID and resistivity measurements. Both compounds exhibit well-localized magnetism due to the presence of trivalent Ce ions. The nickel-based compound orders antiferromagnetically at TN ¼ 10 K; whereas that containing copper remains paramagnetic down to 2 K. The electrical resistivity of CeNi0.6Ga6 has a metallic character and shows pronounced crystal field effects at low temperatures. q 2002 Elsevier Science Ltd. All rights reserved. PACS: 75.30.Mb; 72.15.Eb; 72.15.Qm
1. Introduction
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Ternary cerium-based intermetallics continue to attract much experimental interest owing to a large variety in their physical properties, which span from valence fluctuations, through Kondo effect and heavy fermion behavior, up to well-localized magnetism with long-range magnetic order. Search for new ternaries sometimes results in eminent discoveries, like recent finding of pressure-induced superconductivity in antiferromagnetic heavy-fermion material CeRhIn5 [1], and ambient-pressure heavy-fermion superconductivity in isostructural paramagnetic compounds CeCoIn5 [2] and CeIrIn5 [3]. The systems Ce – Ni – Ga and Ce – Cu – Ga comprise several ternary phases [4] but only very few of them have been characterized with respect to their magnetic behavior. Relatively well studied have been antiferromagnetically ordered Kondo lattices CeCuGa [5] and CeCuGa3 [6], as well as the alloy series Ce(Ni,Ga)4, which exhibits the interplay of Kondo effect and ferromagnetism [7 – 9]. Recently we reported on intermediate valent character of Ce2Ni2Ga [10] and the coexistence of Kondo interactions and antiferromagnetism in CeNiGa2 [10,11]. The latter
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Keywords: A. Intermetallic compounds; A. Magnetically ordered materials; D. Magnetic properties; D. Electronic transport
* Corresponding author. Tel.: þ48-71-34-350-21; fax: þ 48-7134-410-29. E-mail address: [email protected] (D. Kaczorowski).
gallide focused particular attention due to its suitability for a study of non-Fermi-liquid state that develops in this stoichiometric, crystallographically well-ordered compound upon suppression of the long-range magnetic ordering by external pressure of only 4 kbar [12,13]. The two compounds investigated in the present work, CeNi0.6Ga6 and CeCu0.6Ga6, were reported for the first time in eighties [4,14], yet to our knowledge no physical data are available in the literature till date. Both crystallize in a tetragonal system, space group P4/mmm, but with different structure types, closely related to one another. In this paper we report on the magnetic properties of both materials and the electrical resistivity of CeNi0.6Ga6.
2. Experimental Polycrystalline samples of CeNi0.6Ga6 and CeCu0.6Ga6 were prepared by melting appropriate amounts of the constituting elements (Ce: 99.95% Ames Lab.; Ni: 99.99%, Chempur; Cu: 99.99%, Heraeus; Ga: 99.999% Chempur) in carbon-glass crucibles using an induction furnace installed in an argon glove box. The buttons were turned over and remelted several times to ensure good homogeneity. The weight losses after melting were below 0.2%. Subsequently the specimens were wrapped with
0038-1098/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 8 - 1 0 9 8 ( 0 2 ) 0 0 2 2 2 - 3
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D. Kaczorowski, Y. Grin / Solid State Communications 122 (2002) 637–640
3. Results and discussion
Fig. 1. Crystal structures of CeNi0.6Ga6 and CeCu0.6Ga6 (upper part) and the two possible variants of the environment for cerium atoms (lower part).
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The metallographic investigation of the sample with nominal composition CeCu0.6Ga6 revealed the single phase material. The EDX analysis yielded the exact composition CeCu0.63(1)Ga6.03(3) being in good agreement with the literature data [4]. The X-ray powder diffraction patterns of CeNi0.6Ga6 and CeCu0.6Ga6 were easily indexed in a primitive tetragonal system with the lattice parameters: a ¼ 426:86ð4Þ pm and c ¼ 1549:59ð8Þ pm for the Ni-containing compound, and a ¼ 431:65ð2Þ pm and c ¼ 768:29ð5Þ pm for the copper one. These values are similar to those reported in the literature [4,14]. No significant foreign lines were observed on both diffractograms, in agreement with the metallographical results. Moreover, the measured X-ray intensities agreed well with the calculated ones, which were obtained assuming the atomic parameters for CeCu0.6Ga6 as given in Ref. [2], and those for CeNi0.6Ga6 as determined in Ref. [14] for the prototype structure of LaNi0.6Ga6. The unit cells of both compounds are shown in the upper part of Fig. 1. The two structures differ in the occupation of the transition metal positions. In CeCu0.6Ga6, the copper atoms are located at a single site with the occupancy of 60%. In turn, there are two positions of the nickel atoms in CeNi0.6Ga6. One of them (Ni1) is fully occupied, and the other one (Ni2) has the occupancy of 20%. The environment of the cerium atoms is consequently quite similar: the first coordination shell consists of 14 gallium atoms (see lower part of Fig. 1). The notable differences occur only in the second coordination shell: (i) the distance between cerium atoms in CeCu0.6Ga6 is larger than that in CeNi0.6Ga6 (d(Ce –Ce) ¼ 432 and 427 pm, respectively); (ii) depending
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molybdenum foil, placed in quartz tubes and annealed in vacuum at 400 8C for 1 month. Quality of the annealed samples were checked by metallographical analysis. The specimen cuts were polished with several diamond-powder-containing polishing fluids. Photographs were taken with a CCD camera on a Zeiss Axioplan 2 optical microscope. Composition of the phases was determined by EDX method using a Phillips CM20 scanning electron microscope. The prepared alloys were additionally investigated by X-ray powder diffraction using a Guinier Huber G670 camera with Cu Ka1 radiation and germanium as an internal standard. The X-ray patterns were evaluated by means of the STOE WinXPOW program package. The structural data were taken from Ref. [4]. Magnetic measurements were carried out in the temperature range 2 – 400 K and in applied magnetic fields up to 5 T using a Quantum Design MPMS-5 SQUID magnetometer. The electrical resistivity was measured over the temperature interval 4.2 –300 K employing a conventional four-point dc technique.
on the local ordering, each cerium atom can have one (see bottom left part of Fig. 1) or two (see bottom right part of Fig. 1) neighboring transition metal atoms, being in the latter case equidistant to the central Ce-atom in CeCu0.6Ga6 (d1(Ce – TM) ¼ d2(Ce – TM) ¼ 384 pm) but having two distinct distances to the Ce-atom in CeNi0.6Ga6 (d1(Ce– TM) ¼ 382 pm and d2(Ce– TM) ¼ 393 pm). The temperature variation of the magnetic susceptibility of CeNi0.6Ga6 is given in Fig. 2. Above 100 K, x 21(T ) follows a Curie– Weiss law with the effective magnetic moment of 2.43(2)mB per formula unit and the paramagnetic Curie temperature close to zero. The experimental meff value is somewhat reduced with respect to that expected for a free Ce3þ ion (2.54mB). At lower temperatures x 21(T ) slightly deviates from a straight line, presumably due to thermal depopulation of crystal field energy levels. As emphasized in upper inset to Fig. 2, at TN ¼ 10ð1Þ K the compound orders antiferromagnetically. The antiferromagnetic nature of this phase transition is corroborated by a characteristic metamagnetic behavior of the magnetization, measured at T ¼ 2 K as a function of magnetic field (see lower inset to Fig. 2). The salient metamagnetic transition occurs in CeNi0.6Ga6 at the critical field Bc ¼ 3 T: The electrical resistivity of CeNi0.6Ga6 (see Fig. 3)
D. Kaczorowski, Y. Grin / Solid State Communications 122 (2002) 637–640
Fig. 2. Temperature dependence of the inverse molar magnetic susceptibility of CeNi0.6Ga6 measured in a field of 0.1 T. The solid line represents a Curie–Weiss fit of the experimental data with the parameters given in the text. The upper inset displays the low temperature susceptibility. The arrow marks the antiferromagnetic phase transition at TN ¼ 10 K: The lower inset presents the field variation of the magnetization in CeNi0.6Ga6, taken at T ¼ 2 K with increasing (full circles) and decreasing (open circles) magnetic field. The dashed line indicates a linear behavior of s(B ) below the metamagnetic transition at Bc ¼ 3 T:
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Fig. 4. Temperature dependence of the inverse molar magnetic susceptibility of CeCu0.6Ga6 measured in a field of 0.5 T. The solid line represents a Curie–Weiss fit of the experimental data with the parameters given in the text. The upper inset displays the low temperature susceptibility. The lower inset presents the field variation of the magnetization in CeCu0.6Ga6, taken at T ¼ 2 K with increasing (full circles) and decreasing (open circles) magnetic field.
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Contrary to its Ni-containing analogue, the CeCu0.6Ga6 compound does not order magnetically down to 2 K. The reciprocal magnetic susceptibility of this compound, given in Fig. 4, exhibits a linear behavior at temperatures above 100 K, yielding the Curie – Weiss parameters: meff ¼ 2:53ð5ÞmB and up ¼ 11ð2Þ K: This effective magnetic moment is nearly equal to the Hund’s rule value for trivalent Ce ion. The positive and relatively high paramagnetic Curie temperature might evidence the presence of magnetic exchange interactions of ferromagnetic character, yet no magnetic ordering is observed in x(T ) at low temperatures (see upper inset to Fig. 4). Similarly to CeNi0.6Ga6, the deviation of the susceptibility from a Curie– Weiss law, observed at low temperatures, presumably results from crystal field interactions. Apparently, also the s(B ) variation taken at T ¼ 2 K exhibits a paramagnetic behavior (see lower inset to Fig. 4), although its strong curvature may hint on magnetic order setting at somewhat lower temperature.
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diminishes almost linearly with decreasing temperature from 290 down to 60 K, and then falls down more rapidly. The curvature of r(T ) in this region results probably from crystal field effects being consistent with the magnetic susceptibility behavior. The antiferromagnetic phase transition at TN ¼ 10 K manifests itself as a distinct kink in the r(T ) curve and as a Fisher – Langer-type anomaly in the temperature dependence of the resistivity derivative (see inset to Fig. 3). Below TN the resistivity keeps declining, most likely mainly due to continuous decrease towards lower temperatures in both spin-disorder and phonon scattering of conduction electrons.
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4. Conclusions The two cerium compounds investigated in this work reveal well-localized magnetism due to the presence of Ce3þ ions. CeNi0.6Ga6 becomes antiferromagnetic below TN ¼ 10 K and exhibits pronounced metamagnetic properties with a critical field of 3 T at 2 K. In contrast, CeCu0.6Ga6 remains paramagnetic down to 2 K. This difference in the magnetic behavior of these two structurally very closely related compounds may be attributed to dissimilar effectiveness of magnetic exchange interactions
D. Kaczorowski, Y. Grin / Solid State Communications 122 (2002) 637–640
Acknowledgments
References
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[1] H. Hegger, C. Petrovic, E.G. Moshopoulou, M.F. Hundley, J.L. Sarrao, Z. Fisk, J.D. Thompson, Phys. Rev. Lett. 84 (2000) 4986.
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DK is grateful to the Max Planck Society for the Advancement of Science for a fellowship. The authors thank Mrs M. Eckert for metallographical studies.
[2] C. Petrovic, P.G. Pagliuso, M.F. Hundley, R. Movshovich, J.L. Sarrao, J.D. Thompson, Z. Fisk, P. Monthoux, J. Phys.: Condens. Matter 13 (2001) L337. [3] C. Petrovic, R. Movshovich, M. Jaime, P.G. Pagliuso, M.F. Hundley, J.L. Sarrao, Z. Fisk, J.D. Thompson, Europhys. Lett. 53 (2001) 354. [4] Yu.N. Grin, Gallides, Metallurgia, Moscow, 1989, in Russian. [5] H. Nakotte, E. Bruck, K. Prokes, F.R. de Boer, J. Kuang, H. Cui, J. Li, F. Yang, IEEE Trans. Magn. 30 (1994) 1202. [6] J.M. Martin, D.M. Paul, M.R. Lees, D. Werner, E. Bauer, J. Magn. Magn. Mater. 159 (1996) 223. [7] Yu.N. Grin, P. Rogl, H. Noe¨l, J. Less-Common Met. 162 (1990) 361. [8] Yu.N. Grin, K. Hiebl, P. Rogl, H. Noe¨l, J. Less-Common Met. 162 (1990) 371. [9] E.V. Sampathkumaran, K. Hirota, I. Das, M. Ishikawa, Phys. Rev. B 47 (1993) 8349. [10] D. Kaczorowski, P. Rogl, Acta Phys. Pol., A 92 (1997) 289. [11] M.D. Koterlin, B.S. Morokhivskii, Yu.N. Grin, Soy. Phys. Solid State 30 (1988) 517. [12] R. Hauser, E. Bauer, G. Hilscher, H. Michor, D. Kaczorowski, Physica B 237–238 (1997) 205. [13] R. Hauser, E. Bauer, A. Kottar, G. Hilscher, D. Kaczorowski, M. Galli, J. Magn. Magn. Mater. 177–181 (1998) 292. [14] Yu.N. Grin, P. Yarmolyuk, I.V. Rozhdestvenskaya, E.I. Gladyshevshii, Soy. Phys. Crystallogr. 27 (1982) 693.
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between Ce atoms (because of the differences in the Ce – Ce interatomic distances as well as in the local arrangement of the transition metal atoms in the second coordination sphere of the cerium atoms) and/or various magnitude of hybridization between conduction- and 4f-electronic states (because of different electron contribution from copper and nickel). In numerous cerium intermetallics the latter mechanism brings about development of Kondo features in the electronic transport properties. The electrical conductivity of CeNi0.6Ga6 has a metallic character but on the basis of its temperature dependence no straightforward conclusion about Kondo effect can be formulated.
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