A two-phase magnetic structure of DySi2

Article abstract of DOI:10.1016/S0304-8853(03)00302-0

Neutron diffraction performed on the powder binary DySi₂ had shown that, at room temperature, the crystal structure could be described by adopting the orthorhombic Imma system with two sites 4e and 8h for Dy and Si, respectively. At 2 K, the antiferromagnetic nature of the compound is confirmed. Two distinct magnetic phases are found with propagation vectors k₁ = [0,0,0] and k₂ = [1/2,2/2,0] with non-collinear magnetic moments μ₁ = 3.58(4)μ_B and μ₂ = 3.34(2)μ_B.

Full text of DOI:10.1016/S0304-8853(03)00302-0

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 267 (2003) 42–45
A two-phase magnetic structure of DySi2
I.P. Semitelou
Physics Laboratory, Electrical and Computer Engineering Department, Democritus University of Thrace, Xanthi, Greece
Received 22 November 2002; received in revised form 24 March2003
Abstract
Neutron diffraction performed on the powder binary DySi2 had shown that, at room temperature, the crystal
structure could be described by adopting the orthorhombic Imma system with two sites 4e and 8h for Dy and Si,
respectively. At 2 K, the antiferromagnetic nature of the compound is confirmed. Two distinct magnetic phases are
found withpropagation vectors k1=[0,0,0] and k2 ¼ ½12; 22; 0Š withnon-collinear magnetic moments m1 ¼ 3:58ð4Þ mB and
m2 ¼ 3:34ð2Þ mB:
r 2003 Elsevier Science B.V. All rights reserved.
Keywords: DySi2; Crystal structure; Magnetic structure; Neutron diffraction; Rare earth; Silicon
1. Introduction
b-TbSi (hexagonal P6 =mcm). The Tb atoms
3
occupy the 1a position (0,0,0) and Si atoms reside
1 2 1
in the 2d position ð ; ; Þ:
3 3 2
The crystallographic as well as the magnetic
properties of binary disilicide compounds with
transition metals or rare earthhave been studied
with reference to their potential technological
applications [1–4].
The LaSi2 and CeSi2 belong to the orthorhom-
bic space group Imma. They crystallize to the a-
GdSi2-type structure in which all the atoms occupy
the same crystallography position 4e(0,14;z). Other
disilicides of the same structure are always
reported as silicon deficient: DySi1.75 [6],
TbSixX1:80 [7], NdSi1.67, and Nd Si1.75 [8].
Mayer et al. [5] reported that the orthorhombic
structure, space group Imma with a-GdSi2-type
structure, is the high-temperature form of TbSi2,
stable when heated to above 1600ꢀC, while at the
low temperatures one finds the AlB2 C32-type of
Magnetic measurements of heavy rare earth
disilicide compounds (R=Gd, Tb, Dy, Ho)
were initially reported by Sekizawa and Yazukochi
[9] and the RSi2 series was reinvestigated by
Pierre et al. [10]. Both works agree that the
RSi2 compounds present antiferromagnetic beha-
vior. The compounds HoSi1.7 [6], TbSix [7],
and NdSi2 [8] order withcomplex magnetic
arrangements.
The ordering temperatures, given in the two
above articles, are slightly different except for the
DySi2, where the difference is significant
(TN ¼ 17 K [9], TN ¼ 10 K [10]). The investigation
of the neutron diffraction’s pattern of DySi1.75 at
1.25 K shows magnetic reflections, which are
related to 3 different propagation vectors [6].
In the present work we investigate, by neutron
diffraction, the magnetic properties of the
E-mail address: jsemi@ee.duth.gr (I.P. Semitelou).
0304-8853/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0304-8853(03)00302-0

ARTICLE IN PRESS
I.P. Semitelou / Journal of Magnetism and Magnetic Materials 267 (2003) 42–45
43
powdered DySi2 compound in order to determine
the magnetic structure and transition temperature.
2. Experimental
The compound DySi2 was prepared by arc
melting of the constituent elements in an atmo-
sphere of the starting materials of purified argon
gas. The preparation and experimental facilities,
procedures, and measuring techniques are those
reported in Ref. [11]. After arc melting, the
samples were vacuum annealed in the temperature
range 900–1000ꢀC for several weeks and subse-
quently quenched in water.
The sample was powdered and examined by
X-ray diffraction. This confirmed that the synthe-
sized compound of DySi2 consisted of a single
phase.
Neutron diffraction experiments were per-
!
formed with the multicounter system of the Siloe
reactor of the Nuclear Research Center of
Grenoble with a graphite monochromator. The
(
wavelengthwas 2.495 A. The DySi2 powdered
specimen was contained in a vanadium can of
10 mm diameter and 30 mm height. Data analysis
over the temperature range (293–4 K) was per-
formed by using program IC-POWLS [12].
Fig. 1. Crystal structure of DySi2.
Due to the orthorhombic distortion ðða À bÞ=aÞ;
it is possible to separate the (h k l) and (k h l)
reflections. The ratios of the observed reflections
(103/013)=0.68, deviate from the ideal value of
the unity for the a-GdSi2-type structure, where all
atoms occupy the same 4e(0,14;z) position. If we
consider, for the DySi2 compound, the a-GdSi2
defect-type structure, the reliability factor becomes
6.8%.
3. Crystal structure
The neutron diffraction patterns collected at 293
and 17 K show neither variation in intensity of the
Bragg peaks nor any extra reflections of magnetic
origin. It was, therefore, concluded that the
ordering temperature should be lower than 17 K.
The crystal structure (Fig. 1) of the compound
has been refined from the 293 K diffraction
pattern. All nuclear peaks in the diagram could
be indexed within the orthorhombic Imma
space group. The lattice parameters were found
4. Magnetic structure determination
(
(
to be a ¼ 4:035ð2Þ A, b ¼ 3:910ð7Þ A and c ¼
(
13:281ð2Þ A. The Dy and Si atoms occupy the
The 2 K neutron diffraction pattern is charac-
terized by the appearance of additional peaks
(Fig. 3), magnetic in origin, when compared to
the 17 K diffraction pattern (Fig. 2). Satellite
symmetry positions 4e(0,14;z) z ¼ 0:6053 and 8h
(0,y;z) y ¼ 0:0752; z ¼ 0:0624; respectively. The
reliability factor RBragg was found equal to 2.7%.

ARTICLE IN PRESS
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I.P. Semitelou / Journal of Magnetism and Magnetic Materials 267 (2003) 42–45
Fig. 2. Neutron diffraction diagram of DySi2 at 17 K. The dotted line corresponds to the observed intensities; fitted profiles are
represented by solid line.
Fig. 3. Neutron diffraction diagram of DySi2 at 2 K. The dotted line corresponds to the observed intensities; fitted profiles are
represented by solid line.
reflections are not detected in the above diagram.
The analysis of the pattern showed that a number
of magnetic peaks could be indexed withtwo
propagation vectors k1 ¼[0,0,0] and k2 ¼ ½12; 22; 0Š:
The observed intensities are in a good agreement
withthe calculated assuming:
withthe corresponding Dy atoms is as follows:
1
Dy1 : 0; ; z;
4
3
4
Dy : 0; ; z;
%
2
3
Dy3 : 12; ; 12 þ z;
4
1
Dy4 : 12; ; 12 À z:
4
*
An antiferromagnetic arrangement of the mo-
ments M1x À M2x þ M3x À M4x (Fig. 4a)
and M1z À M2z þ M3z À M4z (Fig. 4a) and,
the magnitude of magnetic moment being
mx=1.8(5) mB and mz ¼ 3:1ð3Þ mB for eachatom.

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I.P. Semitelou / Journal of Magnetism and Magnetic Materials 267 (2003) 42–45
45
in the interaction distances as the positional
parameters of the Dy and Si atoms change
(zDy ¼ 0:605320:5997; ySi ¼ 0:075220:0769 and
zSi ¼ 0:062420:0439).
A qualitative treatment of Dy crystal field bases
in the charge point model shows that the
anisotropy along the a-axis is greater than that
along c-axis. Instead, experimentally determined
directions of the Dy moment show the different
magnetic anisotropy along a- and c-axis of the
crystal.
(a1)
Further investigation by neutron diffraction and
susceptibility measurements in DySi2 monocrystal
must be realized in order to determine the Dy
anisotropy direction.
Acknowledgements
(b)
(a2)
The author whishes to express sincere thanks to
Dr. E. Roudaut for his assistance in the experi-
ments.
Fig. 4. Projections of the different magnetic structures along
the a; b or a; c planes: (a) magnetic structure for DySi2,
corresponding to k1 ¼[0,0,0], and (b) magnetic structure for
DySi2, corresponding to k2 ¼ ½12; 22; 0Š:
*
A Collinear arrangement withmagnetic mo-
References
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tion on the (a, b) plane and the a-axis (Fig. 4b).
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