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Magnetic structure of the antiferromagnetic Kondo stannide Ce2Ni2Sn
Physica B 259—261 (1999) 46—47
Magnetic structure of the antiferromagnetic Kondo stannide Ce Ni Sn D. Laffargue , F. Boure´e, B. Chevalier *, J. Etourneau , T. Roisnel ICMCB, CNRS, Avenue du Dr A. Schweitzer, 33608 Pessac Cedex, France Laboratoire Le& on Brillouin (CEA-CNRS), CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
Abstract Magnetization and electrical resistivity measurements on the Ce Ni Sn ternary stannide suggest the occurrence of antiferromagnetic ordering below ¹ "4.7 K. Neutron powder diffraction (NPD) shows that Ce Ni Sn is magnetically , ordered at ¹"1.5 K: magnetic Bragg peaks can then be indexed with a commensurate wave vector, k " (0 0 ), and the Ce Ni Sn magnetic structure described as a collinear arrangement of Ce-moments. Two components of the Ce-magnetic moment M only are obtained from NPD, which are respectively parallel (M ) and perpendicular (M ) to , , k (M "0.335(10) l ). The value of the resulting magnetic moment M is a function of the orientation of M within (a, b) , , plane and lies in the interval 0.41(5))M)0.53(5) l /Ce>, far below g J"2.14 l /Ce>. 1999 Published by ( Elsevier Science B.V. All rights reserved. Keywords: Ce Ni Sn stannide; Neutron powder diffraction; Antiferromagnetic structure
Ce Ni Sn which shows structural relationship with the Kondo insulator stannide CeNiSn, can be classified as an antiferromagnetic Kondo system with ¹ 8 K and ) ¹ "4.7 K as Kondo and Ne´el temperatures, respective, ly [1]. Its investigation by Ce resonant photoemission spectroscopy reveals that these physical properties are governed by a strong contribution of the 4f(Ce) electrons at the Fermi level E [2]. Moreover, the 4f(Ce)-3d(Ni) $ and 5p(Sn) hybridization plays an important role on the behaviour of this stannide. In order to obtain more information on the strength of the 4f(Ce)-ligands hybridization, we have performed neutron powder diffraction (NPD) on Ce Ni Sn; the value of Ce-moment is sensible to this hybridization. Ce Ni Sn sample was prepared by arc-melting stoi chiometric amounts of the constituent elements under argon atmosphere. The obtained alloy was then annealed
* Corresponding author. Tel.: #33-(0)5-56-84-63-36; fax: #33-(0)5-56-84-27-61; e-mail: [email protected].
for two weeks at 800°C in a quartz crucible sealed under vacuum. NPD experiments have been performed at the Orphe´e reactor (Saclay, France), on G4.1 [800 cell PSD, j"2.425 As ] 2-axis diffractometer [3]. Neutron data were analysed with the Rietveld-type FULLPROF program [4], using scattering neutron lengths from [5]: b "0.4840;10\ cm, b "1.0300;10\ cm and ! , b "0.6225;10\ cm. The Ce> magnetic form factor 1 was calculated in the dipolar approximation, 1 j 2# c 1 j 2, with 1 j 2 and 1 j 2 values from [6]. NPD data at T"10 K (5°)2h)85°) were refined, according to orthorhombic Immm space group, W CoB -type crystal structure [1], with subsequent atomic positions: Ce (4j : 0 z ); Ni (4h : 0 y 1/2); Sn ! , (2a : 0 0 0). We got: a"4.4089(5) As , b"5.7192(6) As , c" 8.512(1) As , z "0.2951(6), y "0.2151(7), with a relia! , bility factor R "5.5%. Let us note that a small amount , of CeNi (+1 weight%) is present in the sample. The above parameters (a, b, c, z ) together with U, V, W, ! g (full-width at half-maximum parameters) and S (scale factor) were then kept constant at low temperature ([¹"1.5 K!¹" 10 K] NPD data: see below).
0921-4526/99/$ — see front matter 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 7 3 4 - 0
D. Laffargue et al. / Physica B 259—261 (1999) 46—47
47
Fig. 1. Ce Ni Sn neutron powder diffraction difference pattern [¹"1.5 K]![¹"10 K] (experimental points; calculated and difference profiles; vertical ticks for 2h magnetic Bragg positions, (0 0 ), (0 0 ) and (0 1 ). Fig. 3. Ce> magnetic moment components at ¹"1.5 K. NPD yields M#M"0.335 l and M#M"0.410 l. The V W V W curves show respectively M (open circles), M (open square) W X and M"M#M#M (full circles versus M (maximum V W X V value 0.355 l). The triangles near horizontal (open) and vertical (full) axes are for a M moment component respectively equal to 0.1; 0.2; 0.3; 0.4 and 0.5 l /Ce>.
Fig. 2. Projection on (a, c)-plane of the commensurate (k"(0 0 )) collinear magnetic structure of Ce Ni Sn (open circle: y"0; solid circle: y").
NPD difference diagram [¹"1.5 K!¹"10 K] is shown in Fig. 1: two peaks of magnetic origin are clearly seen, which cannot be accounted for in the crystallographic a;b;c unit-cell. To index these peaks, the search for a commensurate propagation vector parallel to one of the main crystallographic axis, leads to k" (0 0 ) only, i.e. to a magnetic unit-cell a;b;2c. Within a;b;c crystallographic unit-cell, there are four “magnetic” atoms: Ce1 ( 0 z ); Ce2 ( 0 1!z ); ! ! Ce3 (0 #z ); Ce4 (0 !z ); with respective mag ! ! netic moments M , M , M and M . Within 5—30° 2h-range, as considered in Fig. 1, and k"(0 0 ), three magnetic peaks ought to have been present: (0 0 ), (0 0 ) and (0 1 ). With the assumption of a collinear magnetic structure, M "e M(e "$1), the
H H “absence” of (0 0 ) implies that e and e are identical, while e and e are opposite to each other (Fig. 2). From intensity analysis, only two components of the Ce-magnetic moment M can be obtained, which are respectively
parallel (M ) and perpendicular (M ) to k-vector. From , , (0 0 ) magnetic intensity, we get M "0.335(10) l , , whatever the orientation of M within (a, b) plane. The , value of M , and consequently of the resulting magnetic , moment M, is then deduced from (0 1 ) magnetic inten ity: these values are depending on the orientation of M within (a, b) plane (Fig. 3). As M goes from a- to , , b-axis, M increases from 0.41(5) to 0.53(5) l /Ce>, [R "7%], far below g J"2.14 l /Ce>. + ( In summary, our NPD experiment has clearly shown that Ce Ni Sn orders antiferromagnetically at low tem perature. The ordered Ce-moment is very small indicating that the local Kondo fluctuations are present in the ordered state of this ternary stannide.
References [1] F. Fourgeot, B. Chevalier, P. Gravereau, L. Fourne`s, J. Etourneau, J. Alloys Compounds 218 (1995) 90. [2] F. Fourgeot, A. Demourgues, J. Avila, M.C. Ascensio, B. Chevalier, Nucl. Instr. and Meth. B 133 (1997) 127. [3] Laboratoire Le´on Brillouin (CEA/CNRS), Equipements expe´rimentaux, 1995. [4] J. Rodriguez-Carvajal, Physica B 192 (1993) 55. [5] V.F. Sears, Neutron News 3 (3) (1992) 26. [6] A.J. Freeman, J.P. Desclaux, J. Magn. Magn. Mater. 12 (1979) 11.
Magnetic structure of the antiferromagnetic Kondo stannide Ce Ni Sn D. Laffargue , F. Boure´e, B. Chevalier *, J. Etourneau , T. Roisnel ICMCB, CNRS, Avenue du Dr A. Schweitzer, 33608 Pessac Cedex, France Laboratoire Le& on Brillouin (CEA-CNRS), CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
Abstract Magnetization and electrical resistivity measurements on the Ce Ni Sn ternary stannide suggest the occurrence of antiferromagnetic ordering below ¹ "4.7 K. Neutron powder diffraction (NPD) shows that Ce Ni Sn is magnetically , ordered at ¹"1.5 K: magnetic Bragg peaks can then be indexed with a commensurate wave vector, k " (0 0 ), and the Ce Ni Sn magnetic structure described as a collinear arrangement of Ce-moments. Two components of the Ce-magnetic moment M only are obtained from NPD, which are respectively parallel (M ) and perpendicular (M ) to , , k (M "0.335(10) l ). The value of the resulting magnetic moment M is a function of the orientation of M within (a, b) , , plane and lies in the interval 0.41(5))M)0.53(5) l /Ce>, far below g J"2.14 l /Ce>. 1999 Published by ( Elsevier Science B.V. All rights reserved. Keywords: Ce Ni Sn stannide; Neutron powder diffraction; Antiferromagnetic structure
Ce Ni Sn which shows structural relationship with the Kondo insulator stannide CeNiSn, can be classified as an antiferromagnetic Kondo system with ¹ 8 K and ) ¹ "4.7 K as Kondo and Ne´el temperatures, respective, ly [1]. Its investigation by Ce resonant photoemission spectroscopy reveals that these physical properties are governed by a strong contribution of the 4f(Ce) electrons at the Fermi level E [2]. Moreover, the 4f(Ce)-3d(Ni) $ and 5p(Sn) hybridization plays an important role on the behaviour of this stannide. In order to obtain more information on the strength of the 4f(Ce)-ligands hybridization, we have performed neutron powder diffraction (NPD) on Ce Ni Sn; the value of Ce-moment is sensible to this hybridization. Ce Ni Sn sample was prepared by arc-melting stoi chiometric amounts of the constituent elements under argon atmosphere. The obtained alloy was then annealed
* Corresponding author. Tel.: #33-(0)5-56-84-63-36; fax: #33-(0)5-56-84-27-61; e-mail: [email protected].
for two weeks at 800°C in a quartz crucible sealed under vacuum. NPD experiments have been performed at the Orphe´e reactor (Saclay, France), on G4.1 [800 cell PSD, j"2.425 As ] 2-axis diffractometer [3]. Neutron data were analysed with the Rietveld-type FULLPROF program [4], using scattering neutron lengths from [5]: b "0.4840;10\ cm, b "1.0300;10\ cm and ! , b "0.6225;10\ cm. The Ce> magnetic form factor 1 was calculated in the dipolar approximation, 1 j 2# c 1 j 2, with 1 j 2 and 1 j 2 values from [6]. NPD data at T"10 K (5°)2h)85°) were refined, according to orthorhombic Immm space group, W CoB -type crystal structure [1], with subsequent atomic positions: Ce (4j : 0 z ); Ni (4h : 0 y 1/2); Sn ! , (2a : 0 0 0). We got: a"4.4089(5) As , b"5.7192(6) As , c" 8.512(1) As , z "0.2951(6), y "0.2151(7), with a relia! , bility factor R "5.5%. Let us note that a small amount , of CeNi (+1 weight%) is present in the sample. The above parameters (a, b, c, z ) together with U, V, W, ! g (full-width at half-maximum parameters) and S (scale factor) were then kept constant at low temperature ([¹"1.5 K!¹" 10 K] NPD data: see below).
0921-4526/99/$ — see front matter 1999 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 8 ) 0 0 7 3 4 - 0
D. Laffargue et al. / Physica B 259—261 (1999) 46—47
47
Fig. 1. Ce Ni Sn neutron powder diffraction difference pattern [¹"1.5 K]![¹"10 K] (experimental points; calculated and difference profiles; vertical ticks for 2h magnetic Bragg positions, (0 0 ), (0 0 ) and (0 1 ). Fig. 3. Ce> magnetic moment components at ¹"1.5 K. NPD yields M#M"0.335 l and M#M"0.410 l. The V W V W curves show respectively M (open circles), M (open square) W X and M"M#M#M (full circles versus M (maximum V W X V value 0.355 l). The triangles near horizontal (open) and vertical (full) axes are for a M moment component respectively equal to 0.1; 0.2; 0.3; 0.4 and 0.5 l /Ce>.
Fig. 2. Projection on (a, c)-plane of the commensurate (k"(0 0 )) collinear magnetic structure of Ce Ni Sn (open circle: y"0; solid circle: y").
NPD difference diagram [¹"1.5 K!¹"10 K] is shown in Fig. 1: two peaks of magnetic origin are clearly seen, which cannot be accounted for in the crystallographic a;b;c unit-cell. To index these peaks, the search for a commensurate propagation vector parallel to one of the main crystallographic axis, leads to k" (0 0 ) only, i.e. to a magnetic unit-cell a;b;2c. Within a;b;c crystallographic unit-cell, there are four “magnetic” atoms: Ce1 ( 0 z ); Ce2 ( 0 1!z ); ! ! Ce3 (0 #z ); Ce4 (0 !z ); with respective mag ! ! netic moments M , M , M and M . Within 5—30° 2h-range, as considered in Fig. 1, and k"(0 0 ), three magnetic peaks ought to have been present: (0 0 ), (0 0 ) and (0 1 ). With the assumption of a collinear magnetic structure, M "e M(e "$1), the
H H “absence” of (0 0 ) implies that e and e are identical, while e and e are opposite to each other (Fig. 2). From intensity analysis, only two components of the Ce-magnetic moment M can be obtained, which are respectively
parallel (M ) and perpendicular (M ) to k-vector. From , , (0 0 ) magnetic intensity, we get M "0.335(10) l , , whatever the orientation of M within (a, b) plane. The , value of M , and consequently of the resulting magnetic , moment M, is then deduced from (0 1 ) magnetic inten ity: these values are depending on the orientation of M within (a, b) plane (Fig. 3). As M goes from a- to , , b-axis, M increases from 0.41(5) to 0.53(5) l /Ce>, [R "7%], far below g J"2.14 l /Ce>. + ( In summary, our NPD experiment has clearly shown that Ce Ni Sn orders antiferromagnetically at low tem perature. The ordered Ce-moment is very small indicating that the local Kondo fluctuations are present in the ordered state of this ternary stannide.
References [1] F. Fourgeot, B. Chevalier, P. Gravereau, L. Fourne`s, J. Etourneau, J. Alloys Compounds 218 (1995) 90. [2] F. Fourgeot, A. Demourgues, J. Avila, M.C. Ascensio, B. Chevalier, Nucl. Instr. and Meth. B 133 (1997) 127. [3] Laboratoire Le´on Brillouin (CEA/CNRS), Equipements expe´rimentaux, 1995. [4] J. Rodriguez-Carvajal, Physica B 192 (1993) 55. [5] V.F. Sears, Neutron News 3 (3) (1992) 26. [6] A.J. Freeman, J.P. Desclaux, J. Magn. Magn. Mater. 12 (1979) 11.