- Email: [email protected]
Incommensurate magnetic ordering in NdNiSn
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 265 (2003) 94–97
Incommensurate magnetic ordering in NdNiSn b A. Szytulaa,*, B. Penca, N. Stusser . a
! Poland M. Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, Solid State Physics, 30-059 Krakow, b Berlin Neutron Scattering Centre, Hahn-Meitner Institute, D-14100 Berlin-Wannsee, Germany Received 31 December 2002; received in revised form 26 February 2003
Abstract Polycrystalline sample of NdNiSn compound has been prepared and studied by powder neutron diffraction measurements. NdNiSn crystallizes in the orthorhombic TiNiSi-type structure (space group Pnma). Below the N!eel temperature equal to 3.0 K the Nd magnetic moments form an incommensurate sine-wave modulated structure described by the propagation vector k=(0, 0.482(1), 0.248(3)). Magnetic moments equal 2.42(9) mB lie in the a2b plane and form the angle of 39 with the b-axis. r 2003 Elsevier Science B.V. All rights reserved. PACS: 61.12.Ld; 61.66.P; 75.50.Ee Keywords: Neodymium compounds; Neutron diffraction; Magnetic structure
The ternary rare earth RNiSn (R=Gd–Er) compounds crystallize in the orthorhombic TiNiSi-type structure [1]. The magnetic and neutron diffraction measurements indicate that these compounds are antiferromagnets with the Ne! el temperature equal to 11.0, 18.5, 6.5, 3.0 and 4.0 K for Gd, Tb, Dy, Ho and Er compounds, respectively [2–12]. These features are well explained by taking into account the crystalline electric field (CEF) effect. For the RNiSn compounds with light rare earth element R, CeNiSn is a Kondo system [13], PrNiSn does not show any magnetic ordering down to 0.9 K [14] while NdNiSn is an antiferromagnet with the Ne! el temperature 2.8 or 3.0 K [14,15].
*Corresponding author. Tel.: +481263248885546; fax: +48126337086. E-mail address: [email protected] (A. Szytula).
This work reports the results of temperaturedependent neutron diffraction experiments carried out on NdNiSn polycrystalline sample. On the basis of these data the parameters of the crystal and the magnetic structure are determined. The polycrystalline NdNiSn sample was prepared by melting of stoichiometric amounts of the constituent elements in a high-purity argon atmosphere. Purity of the starting materials was 3 N for Nd and 4 N for Ni and Sn. The sample was annealed at 500 C for 7 days. In order to check the purity of the obtained sample X-ray powder diffraction measurements were performed. The results reveal that the sample is a single phase with the orthorhombic TiNiSi-type structure. Neutron diffraction patterns were obtained using E6 diffractometer at the BERII research reactor (Hahn-Meitner Institute). The incident neutron ( Diffraction patterns were wavelength was 2.378 A. recorded at the following temperatures: 1.5, 1.8,
0304-8853/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0304-8853(03)00229-4
ARTICLE IN PRESS A. Szytula et al. / Journal of Magnetism and Magnetic Materials 265 (2003) 94–97
S1 ðx; 14; zÞ; S2 ðx; % 34; z%Þ; S3 ð12 x; 34; 12 þ zÞ and S4 ð12 þ x; 14; 12 zÞ: The Bertaut theory [17] constructed on the basis of an irreducible representation for spin transformation of the 4(c) site in the space group Pnma gives three antiferromagnetic structures described by the vectors: G ¼ S1 S2 þ S3 S4 ; C ¼ S1 þ S2 S3 S4 ; A ¼ S1 S2 S3 þ S4 : The best fit to the experimental data was obtained for a collinear magnetic structure described by the vector A. Nd moments lie in the a–b plane and form an angle (of 39 for S1 and S4 while for S2 and S3 an angle of 141 ) with the baxis. Projection of this structure onto the a2b plane is shown in Fig. 2. The temperature dependence of the 0 1 0 and 0 0 1 reflections leads to the Ne! el temperature of TN ¼ 3:0 K (see the inset in Fig. 1). The Nd moment equal 2.42(9) mB is smaller than the one for free Nd3+ ion (3.27 mB). Magnetization measurements show the metamagnetic transition with the critical field HC ¼ 0:9 T and the value of
NdNiSn
201 -
011 -
001 -
010 -
T=1.5 K
1.4
010 001 -
1.2
T=4.9 K I obs I cal I obs -I cal Bragg positions
1.0
I [a. u.]
Number of counts [a. u.]
0.8 0.6 0.4 0.2 0.0 1.5
2.0
2.5
3.0
10
20
30
40
50
103 301 020 013
112 211 202
200 111 102 201
T [K]
101
2.3, 2.8, 3.1 and 4.9 K. The Rietveld-type program FullProf [16] was used to process the neutron diffraction data. The neutron diffraction pattern recorded at 4.9 K i.e. at paramagnetic state (Fig. 1) confirmed that NdNiSn has the orthorhombic crystal structure of the TiNiSi-type (space group Pnma, no. 61). The atoms are placed at the 4(c) sites: x; 14; z; x; % 34; z%; 12 x; 34; 12 þ z; 12 þ x; 14; 12 z with different values of x and z parameters. These parameters were refined by least-squares method using the intensities of nuclear reflections. Table 1 lists them together with the lattice parameters. The neutron diffractogram of NdNiSn recorded at 1.5 K shows a few additional small intensity peaks of magnetic origin, which were indexed within a magnetic unit cell characterized by the propagation vector k=(0, 0.482(1), 0.248(3)). Nd magnetic moments equal 2.42(9) mB form an incommensurate sine wave modulated structure. The propagation vector k is close to k’ ¼ ð0; 12; 14Þ which corresponds to a long-period commensurate structure. The Nd magnetic moments are located in the crystal unit cell at the following sites:
95
60
70
80
o
2Θ [ ] Fig. 1. Neutron diffraction patterns of NdNiSn collected at 1.5 and 4.9 K. The squares represent the experimental points; the solid lines are the calculated profiles for the model crystal and magnetic structures described in the text and the differences between the observed and the calculated intensities (in the bottom of each diagram). The vertical bars indicate the Bragg peaks of the nuclear and the magnetic phase. The insets show: the enlargement of the low temperature part of the pattern (in the top) and temperature dependencies of the magnetic peak intensities (below).
the magnetic moment 1.77 mB at H ¼ 4 T and T ¼ 2 K [15]. The large interatomic distances between the Nd atoms together with the modulated character of the magnetic order suggest that the magnetic interactions in NdNiSn base on an indirect exchange between the 4f electrons located at different crystallographic sites. This interaction goes highly probably via the conduction electrons (RKKY model). In this mechanism the ordering temperature TN is proportional to the factor G ¼ ðgJ 1Þ2 JðJ þ 1Þ where gJ is the Lande! factor and
ARTICLE IN PRESS A. Szytula et al. / Journal of Magnetism and Magnetic Materials 265 (2003) 94–97
96
Table 1 Crystal data for NdNiSn at T ¼ 10 K
x z
( a ¼ 7:3613(25) A ( b ¼ 4:5221ð15Þ A ( c ¼ 7:6583ð24Þ A
Nd
Ni
Sn
0.0116(22) 0.6981(9)
0.1921(13) 0.0866(13)
0.3109(20) 0.4087(24) RBragg ¼ 4:6% RRF ¼ 5:6%
is necessary to know the values of the crystal electric field parameters. S2
S3 S4
b
S1
a Fig. 2. Projection of the magnetic structure of NdNiSn on to the a2b plane.
J is the total angular momentum of the considered rare earth ion. Applying that theory to the RNiSn compound and taking into account TN ¼ 11 K for GdNiSn [2] yields TN ¼ 1:2 K for NdNiSn, which is significantly smaller than the experimental value. This indicates that the magnetic ordering is not solely governed by the RKKY interactions. Similar observation was made for the isostructural series RPdSn [18] for which the CEF influencing the J states should be considered. The Nd3+ ion contains 3f electrons. Within the Russel–Saunders schema the f 3 system is characterized by the total angular momentum J ¼ 92 8 (L ¼ 6; S ¼ 32; the Lande! factor g ¼ 11 ) and the 4 Hund’s rules ground multiplied I9/2. CEF interactions of Nd3+ ions in the orthorhomic symmetry abolish the 10-fold degeneracy and produce five Kramers doublets. The specific heat data indicate that the ground state is a doublet and the first excited state is also a doublet located at 60 K [14]. The observed value of the Nd magnetic moment originates from mixing of different states. For the detailed analysis of the value of the Nd moment it
Acknowledgements This work was supported by the European Commission under the Access to Research Infrastructures of the Human Potential Programme (contract no. HPRI-CT-1000-00020). The authors (AS and BP) would like to express their gratitude to the management of the Berlin Neutron Scattering Center for financial support and kind hospitality.
References [1] D. Rossi, R. Marazza, R. Ferro, J. Less-Common Met. 107 (1985) 99. [2] Ch.D. Routsi, J.K. Yakinthos, H. Gamari-Seale, J. Magn. Magn. Mater. 98 (1991) 257. [3] P.A. Kotsanidis, J.K. Yakinthos, E. Roudaut, J. Magn. Magn. Mater. 124 (1993) 51. [4] P.A. Kotsanidis, J.K. Yakinthos, E. Ressouche, V.N. Nguyen, J. Magn. Magn. Mater. 131 (1994) 135. [5] J.K. Yakinthos, Ch.D. Routsi, E. Roudaut, J. Magn. Magn. Mater. 136 (1994) 65. [6] P.A. Kotsanidis, J.K. Yakinthos, I. Semitelou, E. Roudaut, J. Magn. Magn. Mater. 116 (1992) 95. [7] J.K. Yakinthos, Ch.D. Routsi, J. Magn. Magn. Mater. 149 (1995) 273. [8] Y. Andoh, M. Kurisu, S. Kawano, I. Oguro, J. Magn. Magn. Mater. 177–181 (1998) 1063. [9] S. Kawano, Y. Andoh, M. Kurisu, J. Magn. Magn. Mater. 182 (1998) 393. [10] Y. Andoh, M. Kurisu, S. Kawano, Physica B 237–238 (1997) 575.
ARTICLE IN PRESS A. Szytula et al. / Journal of Magnetism and Magnetic Materials 265 (2003) 94–97 [11] M. Kurisu, H. Hori, M. Furusawa, M. Miyake, Y. Andoh, I. Oguro, K. Kindo, T. Takeuchi, A. Yamagishi, Physica B 201 (1994) 107. [12] A. Szytula, B. Penc, E. Ressouche, J. Alloys Compounds 224 (1996) 94. [13] Ch.D. Routsi, J.K. Yakinthos, H. Gamari-Seale, J. Magn. Magn. Mater. 117 (1992) 79.
97
[14] M. Kurisu, R. Hara, G. Nakamoto, Y. Andoh, S. Kawano, D. Schmitt, Physica B 312–313 (2002) 861. [15] B. Chevalier, F. Fourgeot, L. Fourn!es, P. Gravereau, G. LeCa.er, J. Etourneau, Physica B 226 (1996) 283. [16] J. Rodriguez-Carvajal, Physica B 192 (1993) 55. [17] E.F. Bertaut, Acta Crystallogr. A 24 (1968) 217. [18] D.T. Adroja, S.K. Malik, Phys. Rev. B 45 (1992) 779.
Journal of Magnetism and Magnetic Materials 265 (2003) 94–97
Incommensurate magnetic ordering in NdNiSn b A. Szytulaa,*, B. Penca, N. Stusser . a
! Poland M. Smoluchowski Institute of Physics, Jagiellonian University, ul. Reymonta 4, Solid State Physics, 30-059 Krakow, b Berlin Neutron Scattering Centre, Hahn-Meitner Institute, D-14100 Berlin-Wannsee, Germany Received 31 December 2002; received in revised form 26 February 2003
Abstract Polycrystalline sample of NdNiSn compound has been prepared and studied by powder neutron diffraction measurements. NdNiSn crystallizes in the orthorhombic TiNiSi-type structure (space group Pnma). Below the N!eel temperature equal to 3.0 K the Nd magnetic moments form an incommensurate sine-wave modulated structure described by the propagation vector k=(0, 0.482(1), 0.248(3)). Magnetic moments equal 2.42(9) mB lie in the a2b plane and form the angle of 39 with the b-axis. r 2003 Elsevier Science B.V. All rights reserved. PACS: 61.12.Ld; 61.66.P; 75.50.Ee Keywords: Neodymium compounds; Neutron diffraction; Magnetic structure
The ternary rare earth RNiSn (R=Gd–Er) compounds crystallize in the orthorhombic TiNiSi-type structure [1]. The magnetic and neutron diffraction measurements indicate that these compounds are antiferromagnets with the Ne! el temperature equal to 11.0, 18.5, 6.5, 3.0 and 4.0 K for Gd, Tb, Dy, Ho and Er compounds, respectively [2–12]. These features are well explained by taking into account the crystalline electric field (CEF) effect. For the RNiSn compounds with light rare earth element R, CeNiSn is a Kondo system [13], PrNiSn does not show any magnetic ordering down to 0.9 K [14] while NdNiSn is an antiferromagnet with the Ne! el temperature 2.8 or 3.0 K [14,15].
*Corresponding author. Tel.: +481263248885546; fax: +48126337086. E-mail address: [email protected] (A. Szytula).
This work reports the results of temperaturedependent neutron diffraction experiments carried out on NdNiSn polycrystalline sample. On the basis of these data the parameters of the crystal and the magnetic structure are determined. The polycrystalline NdNiSn sample was prepared by melting of stoichiometric amounts of the constituent elements in a high-purity argon atmosphere. Purity of the starting materials was 3 N for Nd and 4 N for Ni and Sn. The sample was annealed at 500 C for 7 days. In order to check the purity of the obtained sample X-ray powder diffraction measurements were performed. The results reveal that the sample is a single phase with the orthorhombic TiNiSi-type structure. Neutron diffraction patterns were obtained using E6 diffractometer at the BERII research reactor (Hahn-Meitner Institute). The incident neutron ( Diffraction patterns were wavelength was 2.378 A. recorded at the following temperatures: 1.5, 1.8,
0304-8853/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0304-8853(03)00229-4
ARTICLE IN PRESS A. Szytula et al. / Journal of Magnetism and Magnetic Materials 265 (2003) 94–97
S1 ðx; 14; zÞ; S2 ðx; % 34; z%Þ; S3 ð12 x; 34; 12 þ zÞ and S4 ð12 þ x; 14; 12 zÞ: The Bertaut theory [17] constructed on the basis of an irreducible representation for spin transformation of the 4(c) site in the space group Pnma gives three antiferromagnetic structures described by the vectors: G ¼ S1 S2 þ S3 S4 ; C ¼ S1 þ S2 S3 S4 ; A ¼ S1 S2 S3 þ S4 : The best fit to the experimental data was obtained for a collinear magnetic structure described by the vector A. Nd moments lie in the a–b plane and form an angle (of 39 for S1 and S4 while for S2 and S3 an angle of 141 ) with the baxis. Projection of this structure onto the a2b plane is shown in Fig. 2. The temperature dependence of the 0 1 0 and 0 0 1 reflections leads to the Ne! el temperature of TN ¼ 3:0 K (see the inset in Fig. 1). The Nd moment equal 2.42(9) mB is smaller than the one for free Nd3+ ion (3.27 mB). Magnetization measurements show the metamagnetic transition with the critical field HC ¼ 0:9 T and the value of
NdNiSn
201 -
011 -
001 -
010 -
T=1.5 K
1.4
010 001 -
1.2
T=4.9 K I obs I cal I obs -I cal Bragg positions
1.0
I [a. u.]
Number of counts [a. u.]
0.8 0.6 0.4 0.2 0.0 1.5
2.0
2.5
3.0
10
20
30
40
50
103 301 020 013
112 211 202
200 111 102 201
T [K]
101
2.3, 2.8, 3.1 and 4.9 K. The Rietveld-type program FullProf [16] was used to process the neutron diffraction data. The neutron diffraction pattern recorded at 4.9 K i.e. at paramagnetic state (Fig. 1) confirmed that NdNiSn has the orthorhombic crystal structure of the TiNiSi-type (space group Pnma, no. 61). The atoms are placed at the 4(c) sites: x; 14; z; x; % 34; z%; 12 x; 34; 12 þ z; 12 þ x; 14; 12 z with different values of x and z parameters. These parameters were refined by least-squares method using the intensities of nuclear reflections. Table 1 lists them together with the lattice parameters. The neutron diffractogram of NdNiSn recorded at 1.5 K shows a few additional small intensity peaks of magnetic origin, which were indexed within a magnetic unit cell characterized by the propagation vector k=(0, 0.482(1), 0.248(3)). Nd magnetic moments equal 2.42(9) mB form an incommensurate sine wave modulated structure. The propagation vector k is close to k’ ¼ ð0; 12; 14Þ which corresponds to a long-period commensurate structure. The Nd magnetic moments are located in the crystal unit cell at the following sites:
95
60
70
80
o
2Θ [ ] Fig. 1. Neutron diffraction patterns of NdNiSn collected at 1.5 and 4.9 K. The squares represent the experimental points; the solid lines are the calculated profiles for the model crystal and magnetic structures described in the text and the differences between the observed and the calculated intensities (in the bottom of each diagram). The vertical bars indicate the Bragg peaks of the nuclear and the magnetic phase. The insets show: the enlargement of the low temperature part of the pattern (in the top) and temperature dependencies of the magnetic peak intensities (below).
the magnetic moment 1.77 mB at H ¼ 4 T and T ¼ 2 K [15]. The large interatomic distances between the Nd atoms together with the modulated character of the magnetic order suggest that the magnetic interactions in NdNiSn base on an indirect exchange between the 4f electrons located at different crystallographic sites. This interaction goes highly probably via the conduction electrons (RKKY model). In this mechanism the ordering temperature TN is proportional to the factor G ¼ ðgJ 1Þ2 JðJ þ 1Þ where gJ is the Lande! factor and
ARTICLE IN PRESS A. Szytula et al. / Journal of Magnetism and Magnetic Materials 265 (2003) 94–97
96
Table 1 Crystal data for NdNiSn at T ¼ 10 K
x z
( a ¼ 7:3613(25) A ( b ¼ 4:5221ð15Þ A ( c ¼ 7:6583ð24Þ A
Nd
Ni
Sn
0.0116(22) 0.6981(9)
0.1921(13) 0.0866(13)
0.3109(20) 0.4087(24) RBragg ¼ 4:6% RRF ¼ 5:6%
is necessary to know the values of the crystal electric field parameters. S2
S3 S4
b
S1
a Fig. 2. Projection of the magnetic structure of NdNiSn on to the a2b plane.
J is the total angular momentum of the considered rare earth ion. Applying that theory to the RNiSn compound and taking into account TN ¼ 11 K for GdNiSn [2] yields TN ¼ 1:2 K for NdNiSn, which is significantly smaller than the experimental value. This indicates that the magnetic ordering is not solely governed by the RKKY interactions. Similar observation was made for the isostructural series RPdSn [18] for which the CEF influencing the J states should be considered. The Nd3+ ion contains 3f electrons. Within the Russel–Saunders schema the f 3 system is characterized by the total angular momentum J ¼ 92 8 (L ¼ 6; S ¼ 32; the Lande! factor g ¼ 11 ) and the 4 Hund’s rules ground multiplied I9/2. CEF interactions of Nd3+ ions in the orthorhomic symmetry abolish the 10-fold degeneracy and produce five Kramers doublets. The specific heat data indicate that the ground state is a doublet and the first excited state is also a doublet located at 60 K [14]. The observed value of the Nd magnetic moment originates from mixing of different states. For the detailed analysis of the value of the Nd moment it
Acknowledgements This work was supported by the European Commission under the Access to Research Infrastructures of the Human Potential Programme (contract no. HPRI-CT-1000-00020). The authors (AS and BP) would like to express their gratitude to the management of the Berlin Neutron Scattering Center for financial support and kind hospitality.
References [1] D. Rossi, R. Marazza, R. Ferro, J. Less-Common Met. 107 (1985) 99. [2] Ch.D. Routsi, J.K. Yakinthos, H. Gamari-Seale, J. Magn. Magn. Mater. 98 (1991) 257. [3] P.A. Kotsanidis, J.K. Yakinthos, E. Roudaut, J. Magn. Magn. Mater. 124 (1993) 51. [4] P.A. Kotsanidis, J.K. Yakinthos, E. Ressouche, V.N. Nguyen, J. Magn. Magn. Mater. 131 (1994) 135. [5] J.K. Yakinthos, Ch.D. Routsi, E. Roudaut, J. Magn. Magn. Mater. 136 (1994) 65. [6] P.A. Kotsanidis, J.K. Yakinthos, I. Semitelou, E. Roudaut, J. Magn. Magn. Mater. 116 (1992) 95. [7] J.K. Yakinthos, Ch.D. Routsi, J. Magn. Magn. Mater. 149 (1995) 273. [8] Y. Andoh, M. Kurisu, S. Kawano, I. Oguro, J. Magn. Magn. Mater. 177–181 (1998) 1063. [9] S. Kawano, Y. Andoh, M. Kurisu, J. Magn. Magn. Mater. 182 (1998) 393. [10] Y. Andoh, M. Kurisu, S. Kawano, Physica B 237–238 (1997) 575.
ARTICLE IN PRESS A. Szytula et al. / Journal of Magnetism and Magnetic Materials 265 (2003) 94–97 [11] M. Kurisu, H. Hori, M. Furusawa, M. Miyake, Y. Andoh, I. Oguro, K. Kindo, T. Takeuchi, A. Yamagishi, Physica B 201 (1994) 107. [12] A. Szytula, B. Penc, E. Ressouche, J. Alloys Compounds 224 (1996) 94. [13] Ch.D. Routsi, J.K. Yakinthos, H. Gamari-Seale, J. Magn. Magn. Mater. 117 (1992) 79.
97
[14] M. Kurisu, R. Hara, G. Nakamoto, Y. Andoh, S. Kawano, D. Schmitt, Physica B 312–313 (2002) 861. [15] B. Chevalier, F. Fourgeot, L. Fourn!es, P. Gravereau, G. LeCa.er, J. Etourneau, Physica B 226 (1996) 283. [16] J. Rodriguez-Carvajal, Physica B 192 (1993) 55. [17] E.F. Bertaut, Acta Crystallogr. A 24 (1968) 217. [18] D.T. Adroja, S.K. Malik, Phys. Rev. B 45 (1992) 779.