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Neutron diffraction study of RPtGe2 (R=Dy, Ho) compounds
Physica B 276}278 (2000) 648}649
Neutron di!raction study of RPtGe (R"Dy, Ho) compounds P.A. Kotsanidis *, W. SchaK fer
Democritos University of Thrace, Physics Laboratory, Electrical and computer Engineering Department, 67100 Xanthi, Greece Bonn University, Neutron Diwraction Group in KFA Ju( lich, Mineralogical Institute, D-52425 Bonn, Germany
Abstract Magnetic structures of ternary RPtGe R"Dy,Ho compounds are determined by neutron di!raction on polycrystal line samples. The compounds crystallize in space group Immm. In DyPtGe the magnetic structure at 4 K is sine modulated and is characterized by the wave vector k "[0.268, 0, 0]. It is transformed at 8 K into a structure also sine modulated with the wave vector k "[0.495, 0, 0] and changes from a longitudinal to a nearly transverse type. The ordered Dy moments are 9.9 l and 8.5 l at 4 and 8 K, respectively. In HoPtGe the magnetic structure at 4.2 K is a canted antiferromagnetic. The ordered moments at Ho sites 4i and 4h are 8.1 l and 4.0 l at 4.2 K and are aligned within the ab- and bc- plane, respectively. 2000 Elsevier Science B.V. All rights reserved. Keywords: Rare earth; Magnetic structure; Neutron di!raction
1. Introduction RPtGe are members of the family of ternary RTM compounds (R"rare earth, T"transitions metals and M"B, C, Si, Ge). These compounds are interesting with respect to their structures and magnetic properties. RPtGe crystallizes in the Ge IrY type [1]. Neutron di!raction measurements have been perfomed in order to determine both the crystallographic parameters and the unknown magnetic structure of the compounds RPtGe (R"Dy, Ho).
1.0926 As . Data analysis was performed by integral intensities re"nements, using the least-squares program ICPOWLS capable of simultaneous re"nements of nuclear and magnetic intensities and modeled by commensurate as well as incommensurate spin con"guration [2]. The nuclear scattering lengths and magnetic form factors were taken from Ref. [3,4].
3. Results and discussion 3.1. Crystal structures
2. Experimental Polycrystalline DyPtGe and HoPtGe were syn thesized by arc melting stoichiometric amounts of high-purity Dy, Ho, Pt and Ge elements. Neutron measurements have been performed on the Bonn University powder di!ractometer SV7 at the RFJ-2 research reactor in the Forschungszentrum JuK lich, at 300, 30, 16, 12, 10, 8, 6 and 4 K for the DyPtGe with a neutron wavelength of 1.1236 As and also at 293, 15, 12, 8, 6 and 4 K for the HoPtGe with a neutron wavelength of * Corresponding author. Fax: #30-541-29310. E-mail address: [email protected] (P.A. Kotsanidis)
The nuclear re#ections of the DyPtGe and HoPtGe are indexed on the basis of an orthorhombic unit cell in space group Immm with R in 4i (0,0,z) and 4h (0,y,1/2), Pt in 8l (0,y, z) and Ge in 4g (0,y,0), 4h and 8l [5,6]. Re"ned value of lattice and atomic positional parameters and the reliability factors R are listed in Table 1. 3.2. Magnetic structures 3.2.1. DyPtGe2 Following the temperature dependence of the strongest magnetic peaks two subsequent magnetic phase transitions have been found to occur around ¹ "14 , and ¹ "5 K. ,
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 3 4 3 - 5
P.A. Kotsanidis, W. Scha( fer / Physica B 276}278 (2000) 648}649
649
Table 1 Crystal structure parameters of RPtGe2 R"Dy,Ho
DyPtGe ¹"30 K
HoPtGe ¹"293 K
Atom
Position
x
y
z
x
y
z
R1 R2 Pt Ge1 Ge2 Ge3
4(i) 4(h) 8(l) 4(h) 4(g) 8(l)
0 0 1/2 1/2 1/2 1/2
0 0.211(5) 0.140(3) 0.078(3) 0.077(5) 0.299(5)
0.290(1) 1/2 0.238(2) 0 1/2 0.352(5)
0 0 1/2 1/2 1/2 1/2
0 0.202(6) 0.145(6) 0.074(3) 0.074(3) 0.295(2)
0.266(4) 1/2 0.235(2) 0 1/2 0.343(5)
DyPtGe2: a"4.290(3) As , b"16.370(1) As , c"8.716(4) As , R "3.5%. HoPtGe2: a"4.321(3) As , b"16.344(3) As , c"8.731(5) As , R "4.7%. Table 2 Magnetic structure parameters of RPtGe DyPtGe
¹"8 K
¹"4 K
HoPtGe
¹"4.2 K
At.
pos.
x
y
z
x
y
z
At.
x
y
z
Dy1 Dy2
4(I) 4(h)
0 0
0 0.797(2)
0.286(5) 1/2
0 0
0 0.787(2)
0.292(5) 1/2
Ho1 Ho2
0 0
0 0.798(3)
0.266(2) 1/2
Magnetic structure type Propagation vector Magnetic moments l[l ] Magnetic moment direction R
Sinusoidal
Sinusoidal
Antiferromagnetic
[0.495,0,0] 8.05 (4)
[0.268,0,0] 9.9 (5)
[0,0,0] Ho1 : 8.1 (3)Ho2: 4.0 (2)
"783(2) A
"903 A
Ho1: "903, d "603 A ?
d "873(3) ? 3.7%
d "03 ? 3.1%
Ho2 : "603, d "903 A ? 5.7%
The additional magnetic re#ections at 8 K are indexed as incommensurate satellite pairs around nuclear reciprocal lattice points without special extinction conditions. The magnetic propagation vector is k "[0.495,0,0]. The neutron intensities are in accordance with an amplitude sine modulation of the Dy moments, lying nearly within the bc-plane [5]. Pure magnetic Bragg scattering at 4 K can be indexed on the basis of a propagation vector k "[0.268,0,0]. The observed magnetic intensities are in accordance with a sine-modulated magnetic order of Dy atoms with moment orientations along the a-axis. 3.2.2. HoPtGe2 The di!raction pattern at 4.2 K exhibits additional Bragg re#ections of magnetic origin [6]. These lines can be indexed on the basis of the chemical unit cell and obey the conditions h#k#l"2n#1. Ho spin generated by the translations (0,0,0) and (1/2, 1/2, 1/2) are antiparallel to each other on both, the 4i and 4h sites. The magnetic structure can be described by sequences of ferromagneti-
cally ordered Ho layers coupled antiferromagnetically along the c- and b-axis for sites 4i and 4h. All the magnetic structure parameters of DyPtGe , and HoPtGe as determined from neutron powder di!raction, are listed in Table 2.
References [1] M. FranC7 ois, G. Venturini, E. McRae, B. Malaman, B. Roques, J. Less - Common Met. 128 (1987) 249. [2] W. Kockelmann, E. Jansen, W. SchaK fer. G. Will, A commensurate and incommensurate structures using powder di!raction data, Report JuK l - 3024 Forschungszentrum (KFA) JuK lich 1995. [3] F. Varley, Neutron News 3 (1992) 26. [4] P.J. Brown, Tables of Magnetic Form Factors, ILL 88BRO 4T, 1988. [5] G. Papathanasiou, P. Kotsanidis, J. Yakinthos, W. SchaK fer, Z. Kristallogr. 213 (1988) 28. [6] G. Papathanasiou, P. Kotsanidis, J. Yakinthos, W. SchaK fer, J. Alloys Compounds.
Neutron di!raction study of RPtGe (R"Dy, Ho) compounds P.A. Kotsanidis *, W. SchaK fer
Democritos University of Thrace, Physics Laboratory, Electrical and computer Engineering Department, 67100 Xanthi, Greece Bonn University, Neutron Diwraction Group in KFA Ju( lich, Mineralogical Institute, D-52425 Bonn, Germany
Abstract Magnetic structures of ternary RPtGe R"Dy,Ho compounds are determined by neutron di!raction on polycrystal line samples. The compounds crystallize in space group Immm. In DyPtGe the magnetic structure at 4 K is sine modulated and is characterized by the wave vector k "[0.268, 0, 0]. It is transformed at 8 K into a structure also sine modulated with the wave vector k "[0.495, 0, 0] and changes from a longitudinal to a nearly transverse type. The ordered Dy moments are 9.9 l and 8.5 l at 4 and 8 K, respectively. In HoPtGe the magnetic structure at 4.2 K is a canted antiferromagnetic. The ordered moments at Ho sites 4i and 4h are 8.1 l and 4.0 l at 4.2 K and are aligned within the ab- and bc- plane, respectively. 2000 Elsevier Science B.V. All rights reserved. Keywords: Rare earth; Magnetic structure; Neutron di!raction
1. Introduction RPtGe are members of the family of ternary RTM compounds (R"rare earth, T"transitions metals and M"B, C, Si, Ge). These compounds are interesting with respect to their structures and magnetic properties. RPtGe crystallizes in the Ge IrY type [1]. Neutron di!raction measurements have been perfomed in order to determine both the crystallographic parameters and the unknown magnetic structure of the compounds RPtGe (R"Dy, Ho).
1.0926 As . Data analysis was performed by integral intensities re"nements, using the least-squares program ICPOWLS capable of simultaneous re"nements of nuclear and magnetic intensities and modeled by commensurate as well as incommensurate spin con"guration [2]. The nuclear scattering lengths and magnetic form factors were taken from Ref. [3,4].
3. Results and discussion 3.1. Crystal structures
2. Experimental Polycrystalline DyPtGe and HoPtGe were syn thesized by arc melting stoichiometric amounts of high-purity Dy, Ho, Pt and Ge elements. Neutron measurements have been performed on the Bonn University powder di!ractometer SV7 at the RFJ-2 research reactor in the Forschungszentrum JuK lich, at 300, 30, 16, 12, 10, 8, 6 and 4 K for the DyPtGe with a neutron wavelength of 1.1236 As and also at 293, 15, 12, 8, 6 and 4 K for the HoPtGe with a neutron wavelength of * Corresponding author. Fax: #30-541-29310. E-mail address: [email protected] (P.A. Kotsanidis)
The nuclear re#ections of the DyPtGe and HoPtGe are indexed on the basis of an orthorhombic unit cell in space group Immm with R in 4i (0,0,z) and 4h (0,y,1/2), Pt in 8l (0,y, z) and Ge in 4g (0,y,0), 4h and 8l [5,6]. Re"ned value of lattice and atomic positional parameters and the reliability factors R are listed in Table 1. 3.2. Magnetic structures 3.2.1. DyPtGe2 Following the temperature dependence of the strongest magnetic peaks two subsequent magnetic phase transitions have been found to occur around ¹ "14 , and ¹ "5 K. ,
0921-4526/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 3 4 3 - 5
P.A. Kotsanidis, W. Scha( fer / Physica B 276}278 (2000) 648}649
649
Table 1 Crystal structure parameters of RPtGe2 R"Dy,Ho
DyPtGe ¹"30 K
HoPtGe ¹"293 K
Atom
Position
x
y
z
x
y
z
R1 R2 Pt Ge1 Ge2 Ge3
4(i) 4(h) 8(l) 4(h) 4(g) 8(l)
0 0 1/2 1/2 1/2 1/2
0 0.211(5) 0.140(3) 0.078(3) 0.077(5) 0.299(5)
0.290(1) 1/2 0.238(2) 0 1/2 0.352(5)
0 0 1/2 1/2 1/2 1/2
0 0.202(6) 0.145(6) 0.074(3) 0.074(3) 0.295(2)
0.266(4) 1/2 0.235(2) 0 1/2 0.343(5)
DyPtGe2: a"4.290(3) As , b"16.370(1) As , c"8.716(4) As , R "3.5%. HoPtGe2: a"4.321(3) As , b"16.344(3) As , c"8.731(5) As , R "4.7%. Table 2 Magnetic structure parameters of RPtGe DyPtGe
¹"8 K
¹"4 K
HoPtGe
¹"4.2 K
At.
pos.
x
y
z
x
y
z
At.
x
y
z
Dy1 Dy2
4(I) 4(h)
0 0
0 0.797(2)
0.286(5) 1/2
0 0
0 0.787(2)
0.292(5) 1/2
Ho1 Ho2
0 0
0 0.798(3)
0.266(2) 1/2
Magnetic structure type Propagation vector Magnetic moments l[l ] Magnetic moment direction R
Sinusoidal
Sinusoidal
Antiferromagnetic
[0.495,0,0] 8.05 (4)
[0.268,0,0] 9.9 (5)
[0,0,0] Ho1 : 8.1 (3)Ho2: 4.0 (2)
"783(2) A
"903 A
Ho1: "903, d "603 A ?
d "873(3) ? 3.7%
d "03 ? 3.1%
Ho2 : "603, d "903 A ? 5.7%
The additional magnetic re#ections at 8 K are indexed as incommensurate satellite pairs around nuclear reciprocal lattice points without special extinction conditions. The magnetic propagation vector is k "[0.495,0,0]. The neutron intensities are in accordance with an amplitude sine modulation of the Dy moments, lying nearly within the bc-plane [5]. Pure magnetic Bragg scattering at 4 K can be indexed on the basis of a propagation vector k "[0.268,0,0]. The observed magnetic intensities are in accordance with a sine-modulated magnetic order of Dy atoms with moment orientations along the a-axis. 3.2.2. HoPtGe2 The di!raction pattern at 4.2 K exhibits additional Bragg re#ections of magnetic origin [6]. These lines can be indexed on the basis of the chemical unit cell and obey the conditions h#k#l"2n#1. Ho spin generated by the translations (0,0,0) and (1/2, 1/2, 1/2) are antiparallel to each other on both, the 4i and 4h sites. The magnetic structure can be described by sequences of ferromagneti-
cally ordered Ho layers coupled antiferromagnetically along the c- and b-axis for sites 4i and 4h. All the magnetic structure parameters of DyPtGe , and HoPtGe as determined from neutron powder di!raction, are listed in Table 2.
References [1] M. FranC7 ois, G. Venturini, E. McRae, B. Malaman, B. Roques, J. Less - Common Met. 128 (1987) 249. [2] W. Kockelmann, E. Jansen, W. SchaK fer. G. Will, A commensurate and incommensurate structures using powder di!raction data, Report JuK l - 3024 Forschungszentrum (KFA) JuK lich 1995. [3] F. Varley, Neutron News 3 (1992) 26. [4] P.J. Brown, Tables of Magnetic Form Factors, ILL 88BRO 4T, 1988. [5] G. Papathanasiou, P. Kotsanidis, J. Yakinthos, W. SchaK fer, Z. Kristallogr. 213 (1988) 28. [6] G. Papathanasiou, P. Kotsanidis, J. Yakinthos, W. SchaK fer, J. Alloys Compounds.