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The antiferromagnetic structure of ErNiC2 ternary carbide
Journal of Magnetism and Magnetic Materials 102 (1991) 71-73 North-Holland
The antiferromagnetic
structure of ErNiC, ternary carbide
J.K. Yakinthos, P.A. Kotsanidis Democritos University of Thrace, Electrical Engineering Department, Physics Laboratov,
67100 Xanthi, Greece
W. Schtifer and G. Will Mineralogisches Znstitut der Vniversitiit Bonn, Poppelsdorfer Schloss, W-5300 Bonn, Germany
Received 23 May 1991; in revised form 13 June 1991
The magnetic structure of the orthorhombic ErNiCs ternary compound was studied by neutron diffraction. The structure is collinear antiferromagnetic. The Nobeltemperature is 8 K. The magnetic unit cell has the same dimensions as the chemical one with a magnetic propagation vector k = [O,O,l]. The erbium moments are oriented along the crystallographic a-axis and have a value of 8.7 pa at 4.2 K.
gated so far are between 7 K (R = Nd) and 25 K (R = Tb) [2]. They present two different types of collinear antiferromagnetic structures with magnetic propagation vectors k = [O,O,ll for TmNiC, [3] and k = [i,i,O] for NdNiC, [31 and TbNiC, [4]. The magnetic moments are oriented parallel
1. Introduction This article is a continuation of our studies on RNiC, ternary carbides which crystallize in the orthorhombic CeNiC, structure [ll. The ordering temperatures of the above compounds investi-
10
20
30 2 Theta
40
50
60
(deg)
Fig. 1. Neutron diffraction diagrams of ErNiC, at 100 K (bottom) and 4.2 K (top). The indexing of nuclear and magnetic reflections is based on the orthorhombic crystallographic unit cell. 0304-8853/91/$03.50
0 1991 - Elsevier Science Publishers B.V. All rights reserved
72
J.K. Yakinthos et al. / ErNiC,
to the u-axis or the c-axis for (Nd, Tm) and Tb respectively. In this article, we report on results of a neutron diffraction study on ErNiC,.
2. Experimental The preparation conditions of polycrystalline ErNiC, have been described previously [2]. X-ray analysis shows that all peaks observed could be indexed in the CeNiC, crystal structure with cell parameters in good agreement with those given in ref. [l]. Conditions concerning neutron diffraction experiments and data analysis are identical to those given in ref. [3]. Diffraction diagrams were taken at 100 !nd 4.2 K using a neutron wavelength of 1.097 A (fig. 1).
3. Crystallographic and magnetic structure The nuclear reflections are indexed according to the non-extinction condition k + 1 = 2n in orthorhombic space group Amm2. The nuclear scattering lengths used for a refinement of the atomic parameters are 8.03, 10.3 and 6.65 fm for Er, Ni and C respectively. The atomic positions are 0, 0, 0 for Er in 2(a), 0.5, 0, 0.615 for Ni in 2(b), and 0.5, 0.152, 0.303 for C in 4(e). The 4.2 K lattice parameters are refined to a = 3.496(4), b = 4.481(4) and c = 6.005(5) A. In the 4.2 K pattern, additional peaks of magnetic origin are observed; they can be indexed on the basis of the chemical cell (see fig. 1). The observed conditions for non-extinction are k + 1
ternary carbide
Table 1 Comparison
of observed
Iobs and calculated
nuclear I&
(k + 1= 2n) and magnetic I,!!&(k + I = 2n + 1) neutron inten-
sities of ErNiC, at 4.2 K according to the least squares refinement calculation with POWLS [5]. Intensities obscured by Al-shields of the cryostat are marked by (*) hkl
I obs
001 010 011 100 101001 110 111012 102 020 021 112 003 120 013 121022 200 103 201 210 113 122 211 202 004 030 023 031 212 014 104220130123 221 131032 114 203 213 222 132 024 005 033 124 300 015 301 204 105 230 223 133 310 040 231 311214041115
824 464 145 81 102 674 206 403 (*) 172 267 245 5 102 87 117 97 71 254 251 (*I 303 12 172 133 103 113
Glc
Irntalc
844 456 150 2 409 198
92 111 224 383
2 186 105 153 94 94 27 81 127 183 112 2 140 81 107 105
138 63 6 9 80 76 105 70 77 245 13 57 41
= 2n + 1. The magnetic structure is characterized by a propagation vector [O,O,l] with a +- . . . spin sequence for the Er atoms in 0, 0, 0 and 0, i, i respectively (fig. 2). The magnetic intensities yield a magnetic moment orientation along the crystallographic u-axis and a value of 8.7(3& per Er3+- ion. A refinement calculation performed with the 4.2 K nuclear and magnetic intensities is simultaneously resulted in a BraggR-value of 7.1%; a comparative list of observed and calculated intensities is given in table 1.
4. Conclusion Fig. 2. Collinear antiferromagnetic K.
structure of ErNiC, at 4.2
In the ErNiC, compound, only the erbium ion is bearer of a magnetic moment. This is con-
J. K. Yakinthos et al. / ErNiC,
firmed by the YNiC, Pauli paramagnet [2]. The 3d nickel band must be totally filled by the compound conduction electrons. The NCel temperature is 8 K. The magnetic structure is the same as that of TmNiC,, which has also the same ordering temperature. The structure consists of ferromagnetic Er layers piled along the c-axis with antiferromagnetic coupling. Adjacent Er sheets are separated by layers composed of non-magnetic Ni and C atoms. Within experimental accuracy, the Er magnetic moment of 8.7~~ is nearly equal to the free ion Er3+ value. The magnetic propagation vector is [O,O,l] and the magnetic moment direction is along the u-axis of the crystal. The crystal field parameter a, [6] is negative for TbNiC,, for which the magnetic moment direction is along the x-axis. ErNiC, is isomorphous to TbNiC,. Consequently, the qrn crystal parameters must be nearly the same, because the lattice parameters of the two ympounds differ only by 0.023, 0.004 and 0.006 A in a, b and c respectively. The a, parameter of ErNiC, is positive. Consequently, the magnetic moment of Er, contrary to that of Tb in TbNiC,, must be perpendicular to c, in agreement with the experimental results.
ternary carbide
73
Acknowledgements Thanks are owed to E. Jansen for helping in the programming and to R. Skowronek in performing the neutron diffraction experiments. This work has been supported by the German Federal Minister for Research and Technology (BMFT) under contract no. 03W12BON.
References [l] W. Jeitschko and M.H. Gerss, J. Less-Common Met. 116 (1986) 147. [2] P. Kotsanidis and J.K. Yakinthos, L. Less-Common Met. 152 (1989) 287. [3] J.K. Yakinthos, P.A. Kotsanidis, W. Schlfer and G. Will, J. Magn. Magn. Mater. 89 (1990) 303. [4] J.K. Yakinthos, P.A. Kotsanidis, W. Schlfer and G. Will, J. Magn. Magn. Mater. 81 (1989) 163. [S] E. Jansen, W. Schiifer and G. Will, J. Appl. Crystallogr. 21 (1988) 228. [6] M.T. Hutchings, Solid State Physics, Vol. 16, eds. F. Seitz and D. Tumbull (Academic Press, New York, 1964) p. 227.
The antiferromagnetic
structure of ErNiC, ternary carbide
J.K. Yakinthos, P.A. Kotsanidis Democritos University of Thrace, Electrical Engineering Department, Physics Laboratov,
67100 Xanthi, Greece
W. Schtifer and G. Will Mineralogisches Znstitut der Vniversitiit Bonn, Poppelsdorfer Schloss, W-5300 Bonn, Germany
Received 23 May 1991; in revised form 13 June 1991
The magnetic structure of the orthorhombic ErNiCs ternary compound was studied by neutron diffraction. The structure is collinear antiferromagnetic. The Nobeltemperature is 8 K. The magnetic unit cell has the same dimensions as the chemical one with a magnetic propagation vector k = [O,O,l]. The erbium moments are oriented along the crystallographic a-axis and have a value of 8.7 pa at 4.2 K.
gated so far are between 7 K (R = Nd) and 25 K (R = Tb) [2]. They present two different types of collinear antiferromagnetic structures with magnetic propagation vectors k = [O,O,ll for TmNiC, [3] and k = [i,i,O] for NdNiC, [31 and TbNiC, [4]. The magnetic moments are oriented parallel
1. Introduction This article is a continuation of our studies on RNiC, ternary carbides which crystallize in the orthorhombic CeNiC, structure [ll. The ordering temperatures of the above compounds investi-
10
20
30 2 Theta
40
50
60
(deg)
Fig. 1. Neutron diffraction diagrams of ErNiC, at 100 K (bottom) and 4.2 K (top). The indexing of nuclear and magnetic reflections is based on the orthorhombic crystallographic unit cell. 0304-8853/91/$03.50
0 1991 - Elsevier Science Publishers B.V. All rights reserved
72
J.K. Yakinthos et al. / ErNiC,
to the u-axis or the c-axis for (Nd, Tm) and Tb respectively. In this article, we report on results of a neutron diffraction study on ErNiC,.
2. Experimental The preparation conditions of polycrystalline ErNiC, have been described previously [2]. X-ray analysis shows that all peaks observed could be indexed in the CeNiC, crystal structure with cell parameters in good agreement with those given in ref. [l]. Conditions concerning neutron diffraction experiments and data analysis are identical to those given in ref. [3]. Diffraction diagrams were taken at 100 !nd 4.2 K using a neutron wavelength of 1.097 A (fig. 1).
3. Crystallographic and magnetic structure The nuclear reflections are indexed according to the non-extinction condition k + 1 = 2n in orthorhombic space group Amm2. The nuclear scattering lengths used for a refinement of the atomic parameters are 8.03, 10.3 and 6.65 fm for Er, Ni and C respectively. The atomic positions are 0, 0, 0 for Er in 2(a), 0.5, 0, 0.615 for Ni in 2(b), and 0.5, 0.152, 0.303 for C in 4(e). The 4.2 K lattice parameters are refined to a = 3.496(4), b = 4.481(4) and c = 6.005(5) A. In the 4.2 K pattern, additional peaks of magnetic origin are observed; they can be indexed on the basis of the chemical cell (see fig. 1). The observed conditions for non-extinction are k + 1
ternary carbide
Table 1 Comparison
of observed
Iobs and calculated
nuclear I&
(k + 1= 2n) and magnetic I,!!&(k + I = 2n + 1) neutron inten-
sities of ErNiC, at 4.2 K according to the least squares refinement calculation with POWLS [5]. Intensities obscured by Al-shields of the cryostat are marked by (*) hkl
I obs
001 010 011 100 101001 110 111012 102 020 021 112 003 120 013 121022 200 103 201 210 113 122 211 202 004 030 023 031 212 014 104220130123 221 131032 114 203 213 222 132 024 005 033 124 300 015 301 204 105 230 223 133 310 040 231 311214041115
824 464 145 81 102 674 206 403 (*) 172 267 245 5 102 87 117 97 71 254 251 (*I 303 12 172 133 103 113
Glc
Irntalc
844 456 150 2 409 198
92 111 224 383
2 186 105 153 94 94 27 81 127 183 112 2 140 81 107 105
138 63 6 9 80 76 105 70 77 245 13 57 41
= 2n + 1. The magnetic structure is characterized by a propagation vector [O,O,l] with a +- . . . spin sequence for the Er atoms in 0, 0, 0 and 0, i, i respectively (fig. 2). The magnetic intensities yield a magnetic moment orientation along the crystallographic u-axis and a value of 8.7(3& per Er3+- ion. A refinement calculation performed with the 4.2 K nuclear and magnetic intensities is simultaneously resulted in a BraggR-value of 7.1%; a comparative list of observed and calculated intensities is given in table 1.
4. Conclusion Fig. 2. Collinear antiferromagnetic K.
structure of ErNiC, at 4.2
In the ErNiC, compound, only the erbium ion is bearer of a magnetic moment. This is con-
J. K. Yakinthos et al. / ErNiC,
firmed by the YNiC, Pauli paramagnet [2]. The 3d nickel band must be totally filled by the compound conduction electrons. The NCel temperature is 8 K. The magnetic structure is the same as that of TmNiC,, which has also the same ordering temperature. The structure consists of ferromagnetic Er layers piled along the c-axis with antiferromagnetic coupling. Adjacent Er sheets are separated by layers composed of non-magnetic Ni and C atoms. Within experimental accuracy, the Er magnetic moment of 8.7~~ is nearly equal to the free ion Er3+ value. The magnetic propagation vector is [O,O,l] and the magnetic moment direction is along the u-axis of the crystal. The crystal field parameter a, [6] is negative for TbNiC,, for which the magnetic moment direction is along the x-axis. ErNiC, is isomorphous to TbNiC,. Consequently, the qrn crystal parameters must be nearly the same, because the lattice parameters of the two ympounds differ only by 0.023, 0.004 and 0.006 A in a, b and c respectively. The a, parameter of ErNiC, is positive. Consequently, the magnetic moment of Er, contrary to that of Tb in TbNiC,, must be perpendicular to c, in agreement with the experimental results.
ternary carbide
73
Acknowledgements Thanks are owed to E. Jansen for helping in the programming and to R. Skowronek in performing the neutron diffraction experiments. This work has been supported by the German Federal Minister for Research and Technology (BMFT) under contract no. 03W12BON.
References [l] W. Jeitschko and M.H. Gerss, J. Less-Common Met. 116 (1986) 147. [2] P. Kotsanidis and J.K. Yakinthos, L. Less-Common Met. 152 (1989) 287. [3] J.K. Yakinthos, P.A. Kotsanidis, W. Schlfer and G. Will, J. Magn. Magn. Mater. 89 (1990) 303. [4] J.K. Yakinthos, P.A. Kotsanidis, W. Schlfer and G. Will, J. Magn. Magn. Mater. 81 (1989) 163. [S] E. Jansen, W. Schiifer and G. Will, J. Appl. Crystallogr. 21 (1988) 228. [6] M.T. Hutchings, Solid State Physics, Vol. 16, eds. F. Seitz and D. Tumbull (Academic Press, New York, 1964) p. 227.