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Mictomagnetic behaviour of CeNi0.84Sn2: A neutron diffraction and magnetic study
ELSEVIER
Physica B 234-236 (1997) 689-691
Mictomagnetic behaviour of CeNio.84Sn2" A neutron diffraction and magnetic study P. Schobinger-Papamantellos a'*, J. Rodriguez-Carvajal b, K. Prokes c, K.H.J. Buschow c aLaboratorium fiir Kristallographie, ETHZ, CH-8092 Ziirich, Switzerland bLaboratoire Lkon Brillouin (CEA-CNRS), Centre d'Etudes de Saclay, 91191, Gif-sur-Yvette, France cVan der Waals-Zeeman Institute, University of Amsterdam, 1018 XE Amsterdam, The Netherlands
Abstract
The magnetic properties of the orthorhombic (Cmcm) antiferromagnetic compound of nominal composition CeNiSn2.1 were studied by magnetisation measurements and neutron diffraction. The refinement of the nuclear structure shows a Ni deficiency, leading to the formula CeNio.84o~4)Sn2. At 1.5 K two magnetic phases coexist in equal amounts. One of these is ferromagnetic ql = 0 with Tc = 3 K. The other phase is an antiferromagnetic modulated phase (antiphase domain type with two amplitudes) with TN = 4.0 K. Its magnetic ordering can be described by two propagation vectors q2 = (010) (Cp magnetic lattice) and q3 = 1/3b*. The ordered magnetic moment value at 1.5 K in both phases is 2.0~tB/Ce atom and points to the same direction along c. Above 2 K the wave vector q3 becomes incommensurate with the crystal lattice. The observation of two magnetic phases is attributed to the occurrence of concentration fluctuations associated with the Ni deficiency. Keywords: Rare-earth metals; Magnetic order; Multi-q structures; Rietveld refinement
CeNiSn2 crystallises with the CeNiSi2 type of structure [1,2] (Cmcm space group) and forms a range of solid solutions characterised by a different degree of Ni deficiency 1"2,3]. The stoichiometric CeNiSn2 orders antiferromagnetically below 3.9 K [2, 4] (0p = 5 K and ~eff 2"431aB) and undergoes a second magnetic phase transition at 2.6K. Magnetic measurements on a powder sample of nominal composition CeNiSn2.1 were made on a S Q U I D magnetometer in the temperature range 1.7-10 K in fields up to 5 T [6] (excess in Sn was =
* Corresponding author.
used to compensate evaporation losses). These show that antiferromagnetic ordering appears at around 4 K and can be broken in fairly low magnetic fields, which is accompanied by a small hysteresis. F o r T < 3 K a ferromagnetic contribution to the magnetisation develops. Very likely both contributions are due to two different coexisting magnetic phases as shown below. Neutron diffraction data (of the same sample) were collected between 1.8 K-293 K and for various wavelengths (2 = 0.1704 and 0.2337 nm) l-7]. The data were evaluated by the program Fullprof [5]. The refinement of the nuclear structure has shown that the sample is Ni deficient CeNio.s4Sn2 (see Table 1, Fig. 1) and contains 4.3% of Ni3Sn2 as impurity. The concentration fluctuations
0921-4526/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S092 1-4526(96)0 1093-9
P. Schobinger-Papamantellos et al. /Physica B 234-236 (1997) 689-691
690
15 C e N i S n 2 10 K
12
et
,,q.
e,I
O0
~ ~4
e~
o~ ~
9
o
~
,~
I
--I
obs cxl
e4
= ~6 e~ •~ 3 = - - I ~ 1 1
I--I--II I
I I
I
II
I
I I
I I I II
I
Ill
IllU
II
I-Ill
II I I I I I I
I
I IIIII
II
IITIll
IIIIIIIII
IIIII
I IIIl IIIIII
LIB I 1 |1111111
8 '~mq
1.5 K - 1 0 K .........
I¢t
~: V
~ 6
• O
. ~
~~-a
I I
.
•
; ,~
I
1 oh6
6 w-{
=4 ,
+
,
ta=,l I
0
-2
0
10
I
I
20
+
I IIII
'
II
+
I I Ill
30
Jl~
~
I IIIOO II Ill II I I I II I l l
40
~
I
',b,
II I Ill I II I III I|11111 I l l l l l l l l l n l l l l l l i l l l l l l l l l l l l
50
60
IIII
IIIIIIll i iillllldl
I°~'I ,
70
80
20 ( d e g . ) Fig. 1. Observed and calculated neutron intensities of CeNiSn2.1. Top part: paramagnetic state at 10 K. The arrows indicate the strongest peaks of the impurity phase NiaSn2. Bottom part: magneticallyordered state at 1.5-10 K (differencediagram)comprisingthree sets of magnetic reflections (wave vectors: ql = 0, q2 = (010) and q3 = 1/3b*).
associated with the vacancy distribution give rise to a nonuniform magnetic ordering throughout the whole sample. At 1.5 K the sample showed a micromagnetic behaviour: roughly half of the sample displays long range antiferromagnetic ordering (Figs. 1 and 2). The other half is the ferromagnetic
phase. Probably the ferromagnetic phase is present as a spin glass or cluster glass for T > 3 K and can be broken easily at higher temperatures in fairly low fields as found for the magnetic measurements. MSR preliminary results indicate the presence of spin-glass at 10 K I-8].
P. Schobinger-Papamantellos et al. /Physica B 234-236 (1997) 689-691
b
691
b
8
,-y C
v C
(a)
(b)
$
b
C
(c)
• Ce',
o cel~
o ce~,l
(d) Fig. 2. Magnetic structures of CeNi0.s4Sn2 at 1.5 K:(a) ferromagnetic parallel component ((100) plane),(b) ferrimagnetic ((0 10) plane), (c) transversal amplitude-modulated structure with wave vector q3 = 1/3b* and the square wave with q2 = (0 1 0) and q3 = 1/3b*. Table 1 Refined parameters of CeNio.s4Sn2 at 10 K and 1.5-10 K. #z is the ferromagnetic moment value (ql = 0). #(2) =/tx/z is the antiferromagnetic moment value (q2 = (010)). #(3) (is the antiferromagnetic moment value giving rise to the transverse amplitude modulated structure along c (q3 = 1/3b*) Parameter
10 K
1.5-10 K
Yc¢ YNi, OCNi Ysnm YSn(2) #z [/~B] /~(2~ [#B], ~(3) [#B] a (nm) b (nm) c (nm) Rn% , Rml% , Rm2°/o
0.1063(5) 0.3169(3), 0.84(1) 0.4505(4) 0.7462(4)
0.1062 --
Rwp% , Rexp% , Z 2
--
-0.44675(8) 1.7869(3) 0.44876(8) 4.5 11.3, 1.6, 53
--1.38(3) 0.29(1) 1.69(3) 0.44672 1.78666 0.44877 - - , 19.6, 18.0 33, 19.3, 2.9
References [1] O.P. Bodak and E.I. Gladyshevskii, Sov. Phys. Crystallogr. 14 (1970) 859. I-2] R.V. Skolozdra and L. Komarovskaya, Izv. Akad Nauk SSSR Met. 2 (1988) 214 (Russ. Metall. Met. 2, (1988) 207); Phys. Mett. Metall. 65 (1988) 99. [3] M. Francois, G. Venturini, B. Malaman and B. Roqucs, J. Less-Common Met. 160 (1990) 197. [4] V.K. Pecharsky, K.A. Gschneidner, Jr. and L.L. Miller, Phys. Rev. B 43 (1991) 10906. 15] J. Rodriguez-Carvajal, Physica B 192 (1993) 55. E6] LW.F.J. Lemmens, G.H. Nieuwenhuys, P. Schobinger Papamantellos and K.H.J. Buschow, to be published. [7] P. Schobinger PapamanteUos, J. Rodriguez-Carvajal, K. Prokes and K.H.J. Buschow, Condensed Matter 8 (1996) 8635. [8] A. Schenk and F. Gygax, private communication (July 1996).
Physica B 234-236 (1997) 689-691
Mictomagnetic behaviour of CeNio.84Sn2" A neutron diffraction and magnetic study P. Schobinger-Papamantellos a'*, J. Rodriguez-Carvajal b, K. Prokes c, K.H.J. Buschow c aLaboratorium fiir Kristallographie, ETHZ, CH-8092 Ziirich, Switzerland bLaboratoire Lkon Brillouin (CEA-CNRS), Centre d'Etudes de Saclay, 91191, Gif-sur-Yvette, France cVan der Waals-Zeeman Institute, University of Amsterdam, 1018 XE Amsterdam, The Netherlands
Abstract
The magnetic properties of the orthorhombic (Cmcm) antiferromagnetic compound of nominal composition CeNiSn2.1 were studied by magnetisation measurements and neutron diffraction. The refinement of the nuclear structure shows a Ni deficiency, leading to the formula CeNio.84o~4)Sn2. At 1.5 K two magnetic phases coexist in equal amounts. One of these is ferromagnetic ql = 0 with Tc = 3 K. The other phase is an antiferromagnetic modulated phase (antiphase domain type with two amplitudes) with TN = 4.0 K. Its magnetic ordering can be described by two propagation vectors q2 = (010) (Cp magnetic lattice) and q3 = 1/3b*. The ordered magnetic moment value at 1.5 K in both phases is 2.0~tB/Ce atom and points to the same direction along c. Above 2 K the wave vector q3 becomes incommensurate with the crystal lattice. The observation of two magnetic phases is attributed to the occurrence of concentration fluctuations associated with the Ni deficiency. Keywords: Rare-earth metals; Magnetic order; Multi-q structures; Rietveld refinement
CeNiSn2 crystallises with the CeNiSi2 type of structure [1,2] (Cmcm space group) and forms a range of solid solutions characterised by a different degree of Ni deficiency 1"2,3]. The stoichiometric CeNiSn2 orders antiferromagnetically below 3.9 K [2, 4] (0p = 5 K and ~eff 2"431aB) and undergoes a second magnetic phase transition at 2.6K. Magnetic measurements on a powder sample of nominal composition CeNiSn2.1 were made on a S Q U I D magnetometer in the temperature range 1.7-10 K in fields up to 5 T [6] (excess in Sn was =
* Corresponding author.
used to compensate evaporation losses). These show that antiferromagnetic ordering appears at around 4 K and can be broken in fairly low magnetic fields, which is accompanied by a small hysteresis. F o r T < 3 K a ferromagnetic contribution to the magnetisation develops. Very likely both contributions are due to two different coexisting magnetic phases as shown below. Neutron diffraction data (of the same sample) were collected between 1.8 K-293 K and for various wavelengths (2 = 0.1704 and 0.2337 nm) l-7]. The data were evaluated by the program Fullprof [5]. The refinement of the nuclear structure has shown that the sample is Ni deficient CeNio.s4Sn2 (see Table 1, Fig. 1) and contains 4.3% of Ni3Sn2 as impurity. The concentration fluctuations
0921-4526/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved PII S092 1-4526(96)0 1093-9
P. Schobinger-Papamantellos et al. /Physica B 234-236 (1997) 689-691
690
15 C e N i S n 2 10 K
12
et
,,q.
e,I
O0
~ ~4
e~
o~ ~
9
o
~
,~
I
--I
obs cxl
e4
= ~6 e~ •~ 3 = - - I ~ 1 1
I--I--II I
I I
I
II
I
I I
I I I II
I
Ill
IllU
II
I-Ill
II I I I I I I
I
I IIIII
II
IITIll
IIIIIIIII
IIIII
I IIIl IIIIII
LIB I 1 |1111111
8 '~mq
1.5 K - 1 0 K .........
I¢t
~: V
~ 6
• O
. ~
~~-a
I I
.
•
; ,~
I
1 oh6
6 w-{
=4 ,
+
,
ta=,l I
0
-2
0
10
I
I
20
+
I IIII
'
II
+
I I Ill
30
Jl~
~
I IIIOO II Ill II I I I II I l l
40
~
I
',b,
II I Ill I II I III I|11111 I l l l l l l l l l n l l l l l l i l l l l l l l l l l l l
50
60
IIII
IIIIIIll i iillllldl
I°~'I ,
70
80
20 ( d e g . ) Fig. 1. Observed and calculated neutron intensities of CeNiSn2.1. Top part: paramagnetic state at 10 K. The arrows indicate the strongest peaks of the impurity phase NiaSn2. Bottom part: magneticallyordered state at 1.5-10 K (differencediagram)comprisingthree sets of magnetic reflections (wave vectors: ql = 0, q2 = (010) and q3 = 1/3b*).
associated with the vacancy distribution give rise to a nonuniform magnetic ordering throughout the whole sample. At 1.5 K the sample showed a micromagnetic behaviour: roughly half of the sample displays long range antiferromagnetic ordering (Figs. 1 and 2). The other half is the ferromagnetic
phase. Probably the ferromagnetic phase is present as a spin glass or cluster glass for T > 3 K and can be broken easily at higher temperatures in fairly low fields as found for the magnetic measurements. MSR preliminary results indicate the presence of spin-glass at 10 K I-8].
P. Schobinger-Papamantellos et al. /Physica B 234-236 (1997) 689-691
b
691
b
8
,-y C
v C
(a)
(b)
$
b
C
(c)
• Ce',
o cel~
o ce~,l
(d) Fig. 2. Magnetic structures of CeNi0.s4Sn2 at 1.5 K:(a) ferromagnetic parallel component ((100) plane),(b) ferrimagnetic ((0 10) plane), (c) transversal amplitude-modulated structure with wave vector q3 = 1/3b* and the square wave with q2 = (0 1 0) and q3 = 1/3b*. Table 1 Refined parameters of CeNio.s4Sn2 at 10 K and 1.5-10 K. #z is the ferromagnetic moment value (ql = 0). #(2) =/tx/z is the antiferromagnetic moment value (q2 = (010)). #(3) (is the antiferromagnetic moment value giving rise to the transverse amplitude modulated structure along c (q3 = 1/3b*) Parameter
10 K
1.5-10 K
Yc¢ YNi, OCNi Ysnm YSn(2) #z [/~B] /~(2~ [#B], ~(3) [#B] a (nm) b (nm) c (nm) Rn% , Rml% , Rm2°/o
0.1063(5) 0.3169(3), 0.84(1) 0.4505(4) 0.7462(4)
0.1062 --
Rwp% , Rexp% , Z 2
--
-0.44675(8) 1.7869(3) 0.44876(8) 4.5 11.3, 1.6, 53
--1.38(3) 0.29(1) 1.69(3) 0.44672 1.78666 0.44877 - - , 19.6, 18.0 33, 19.3, 2.9
References [1] O.P. Bodak and E.I. Gladyshevskii, Sov. Phys. Crystallogr. 14 (1970) 859. I-2] R.V. Skolozdra and L. Komarovskaya, Izv. Akad Nauk SSSR Met. 2 (1988) 214 (Russ. Metall. Met. 2, (1988) 207); Phys. Mett. Metall. 65 (1988) 99. [3] M. Francois, G. Venturini, B. Malaman and B. Roqucs, J. Less-Common Met. 160 (1990) 197. [4] V.K. Pecharsky, K.A. Gschneidner, Jr. and L.L. Miller, Phys. Rev. B 43 (1991) 10906. 15] J. Rodriguez-Carvajal, Physica B 192 (1993) 55. E6] LW.F.J. Lemmens, G.H. Nieuwenhuys, P. Schobinger Papamantellos and K.H.J. Buschow, to be published. [7] P. Schobinger PapamanteUos, J. Rodriguez-Carvajal, K. Prokes and K.H.J. Buschow, Condensed Matter 8 (1996) 8635. [8] A. Schenk and F. Gygax, private communication (July 1996).