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Magnetic characteristics of some RNiSn (R = Ce, Pr, Nd, Sm) and RRhSn (R = Ce, Pr, Nd) compounds
Journal of Magnetism and Magnetic Materials 117 (1992) 79-82 North-Holland
Magnetic characteristics of some RNiSn (R = Ce, Pr, Nd, Sm) and RRhSn (R = Ce, Pr, Nd) compounds C h . D . R o u t s i , J.K. Y a k i n t h o s Democritos University of Thrace, Electrical Engineering Department, Physics Laboratory, 67100 Xanthi, Greece
and
H. G a m a r i - S e a l e Institute of Material Science, NSRC Democritos, 153.10Aghia ParaskeviAttiki, Greece
Received 24 April 1992
Magnetic properties of seven equiatomic ternary RNiSn and RRhSn compounds(R = light rare earth) have been studied in fields of up to 20 kOe in the temperature range 4.2-200 K. It has been found that all compoundsfollow the Curie-Weiss law above 40 K, except CeNiSn and CeRhSn which do not show Curie-Weiss behavior at any temperature. The latter show a Kondo or valence fluctuation behavior. The compound SmNiSn orders antiferromagneticallywith a N6el temperature = 9 K. No ordering temperature was observed down to 4.2 K for the rest of the compounds.
1. Introduction The compounds RNiSn and R R h S n with heavy R elements have already been studied in our previous papers [1,2]. The susceptibility of YTSn (T -- Ni, Rh) is temperature independent and the moment of nickel and rhodium was found to be zero in the whole series. In the nickel series the compounds with Gd, Th and Dy are antiferromagnetic at low temperatures while no ordering temperature was observed down to 4.2 K for the compounds with Ho, Er and Tm. The GdRhSn, ThRhSn and DyRhSn compounds order antiferromagnetically with N6el temperatures 14.8, 18.4 and 8 K respectively. TbRhSn presents a second small susceptibility maximum at 6.2 K, perhaps suggesting a change in the magnetic structure
Correspondence to: Dr. Ch.D. Routsi, Democritos University of Thrace, Electrical Engineering Department, Physics Laboratory, 67100 Xanthi, Greece.
within the ordered range. The H o R h S n and ErRhSn compounds do not show any magnetic ordering down to 4.2 K. The crystal structure of the R R h S n series with R -- heavy rare earth was determined by Dwight e t al. [3]. In this paper, a continuation of our systematic study of the RTSn (T = transition metal) equiatomic compounds, we determine the crystal structure of the R R h S n series with R = light rare earth and study its macroscopic magn e t i c p r o p e r t i e s as well as those of the RNiSn series, with R = Ce, Pr, Nd, Sm.
2. Experimental The preparation as well as the magnetic susceptibility measurement techniques of RTSn (T = Ni, Rh) are described in ref. [1]. The compounds were examined by X-ray analysis and were found to be single-phased. The compounds
0304-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
Ch.D. Routsi et al. / Characteristics of RNiSn and RRhSn compounds
80
CeRhSn, PrRhSn and NdRhSn were found to crystallize in a hexagonal unit cell with a and c parameters given in table 1. Using the LazyPulverix program [4], the best fit for the observed intensity of reflections in the RRhSn (R = Ce, Pr, Nd) series was achieved for the atom sites, of the hexagonal type FeEP crystal structure (space group P62m), given by Dwight et al. [3] and not those given by Hovestreydt et al. [5]. The compounds RNiSn were found to crystallize in the orthorhombic TiNiSi type (space group Pnma) and their lattice parameters are in good agreement with those determined by Rossi et al. [6].
J 70
o
PrNiSn NdNiSn
60
H=IKOe 80
40
3O
H = 2 0 0 Oe
3. Results and discussion
---.... 2 0
i 3.1. RNiSn compounds (R = Ce, Pr, Nd, Sm) lO
The reciprocal susceptibility vs. temperature for the RNiSn compounds is presented in figs. 1 and 2. PrNiSn follows a Curie-Weiss law from 30 K to the highest available temperature. From this part of the graph a negative paramagnetic Curie temperature (Op) is derived equal to - 1 0 K indicating that antiferromagnetic interactions are predominant. The experimental /.%el= 3.67/z a is found to be slightly greater than the theoretically calculated /.Lth=gj[J(J+ 1)] 1/2 for the free tripositive rare-earth ion. Similar results have been obtained for PrNiA1 [7] and for PrPtSn [2] which do not show any ordering down to 4.2 K either, with/xeff = 3.75/x a and @p = - 10 K (see table 2). NdNiSn exhibits Curie-Weiss behavior above 30 K and a/xeff equal to 4.2t~B which is also slightly larger than that of the tripositive ion. The compound does not show any ordering down to 4.2 K. SmNiSn orders antiferromagnetically, presenting
0
40
80
120
160
T(K)
Fig. 1. Reciprocal susceptibility vs. temperature of PrNiSn and NdNiSn compounds.
a susceptibility maximum at 9 K. There is a second very small maximum in the susceptibility below T N (at --- 5 K) which may correspond to a magnetic transition similar to that observed in SmPdSn compound [8]. A neutron diffraction study of TbNiSn, now in progress in our laboratory, shows that this compound also presents two different magnetic structures below T N. CeNiSn does not show Curie-Weiss behaviour at any temperature. The graph X -1 vs. T concaves downwards and the susceptibility values are much smaller than those expected from the Curie law.
Table 1 Lattice constants of RRhSn (R = Ce, Pr, Nd) compounds with the FezP-type structure and atomic positions for PrRhSn Compound
a (,A)
c (,~)
Atom
Position
x
y
z
CeRhSn PrRhSn NdRhSn
7.55 7.539 7.53
3.97 3.92 3.89
Pr Sn Rh I Rh n
3(8) 3(f) l(b) 2(c)
x x 0 ½
0 0 0 ~
½ 0
Xpr = 0.605, Xs, = 0.265.
1
0
Ch.D. Routsi et al. / Characteristics of RNiSn and RRhSn compounds
•
CeNiln
•
ImNilln
81
2.30
16(
•00
120
•OO
E = 1.0o E
400
SO
FI
1.711 40
200
/ / /
0
/
o
4~
i • 4TIK)
.'o
i
i
12
16
' =
1~0
160
I
1.50 0.30
T(K)
2.00
iogT(K)
F i g . 3.
Reciprocal susceptibility vs. temperature under 1 kOe of CeNiSn and SmNiSn compounds (insert: susceptibility variation at low temperatures of SmNiSn compound). F i g . 2.
The influence of the crystal field or spin compensation by the conduction electrons (Kondo phenomenon), or both, may be responsible. Similar behavior was observed in CeNiAI [7]. The data in fig. 3 show that the measured inverse susceptibility X- 1 is linear with T °'3 suggesting that CeNiSn is a Kondo system. Leon et al. [7] found a T °'57 dependence of X - 1 for the CeNiAI compound. The isotherms of all compounds at ~ 4.5 K are straight lines passing from the origin (fig. 4).
1.50
1.00
0
Log-log plot of X - 1 fit y =
VS.
temperature for CeNiSn. Best
0 . 3 x + 1.65.
Curie-Weiss law above 40 K (fig. 5) approximately. Their paramagnetic Curie temperatures are + 10 and + 12 K respectively. In the paramagnetic region, their effective magnetic moments /Zeff are found to be in good agreement with the theoretical ~th for Pr 3+ and N d 3+. Down to 4.2 K the compounds do not show any ordering. No Curie-Weiss behavior is observed for CeRhSn (fig. 5). The dependence of the inverse
2oo I •
3.2. RRhSn compounds (R = Ce, Pr, Nd)
CeNiSn
/
o PrNiSn
o .,.,s.
The reciprocal susceptibility vs. temperature of the PrRhSn and NdNhSn compounds follows the Table
/
• SmNiSn
"
#
2
and the N~el temperature of the RNiSn and compounds
Compound
/'/'off
gJ[J(J + 1)] x/2
CeNiSn
-
2.56
-
-
PrNiSn NdNiSn
3.67 4.2
3.62 3.68
- 10 - 4
-
Op
T N (K)
SmNiSn
1.37
1.55
- 40
9
CeRhSn
-
2.56
-
-
PrRhSn
3.83
3.62
+ 10
-
NdRhSn
3.55
3.68
+ 12
-
-~
/
j
T,4.0 K 120 AX e
/zeff, /~t,, @p RRhSn
100
T,4.1B K
0
E
T,4.2K
"~'ao E e
I 40
0
4
•
12
16
20
HIKOe)
F i g . 4.
Magnetization vs. applied field at compounds.
4.5 K
of the
RNiSn
Ch.D. Routsi et al. / Characteristics of RNiSn and RRhSn compounds
82
60
•
CeRhSn
•
NdRhSn
susceptibility on temperature of CeRhSn is similar to that of CeNiSn suggesting a Kondo state or valence fluctuation. The slope of the variation of X-1 vs. T of CeRhSn is more pronounced than that of CeNiSn. The sharp increase of X is attributed, after Buffat et al. [9] to small amounts of stable C e 3 + ions stabilized by lattice defects or to traces of other magnetic rare earth ions. Isotherms of CeRhSn, PrRhSn and NdRhSn are shown in fig. 6. The magnetization of the Nd compound shows saturation at 4.2 K under a field of 4 kOe suggesting a ferromagnetic behavior. For all the RNiSn and RRhSn compounds, the values of the magnetic moments at 4.5 K under 20 kOe are much smaller than gjJ for the R 3+ free ion, indicating that saturation was not reached.
PrRhSn
50
40
160
30
120
20
BO
l) D 0
E v
L,
10
40
Y 0
40
80
120
0
References
T(K)
Fig. 5. Reciprocal susceptibility vs. temperature at 1 kOe of RRhSn with R = Ce, Pr, Nd. CeRhSn Pr RhSn • NdRhSn • /
~
/ /
lol-
,/ -"~ T : 4 . 6 K
'il / [1
/
,o
/
~
2
0
200
p
T:IoaK
"--'"
4
8
x10-1
1'2
40
16
20
0
H(KOe)
Fig. 6. Magnetization vs. applied field of RRhSn with R = Ce, Pr, Nd.
[1] Ch. Routsi, J.K. Yakinthos and H. Gamari-Seale, J. Magn. Magn. Mater. 98 (1991) 257. [2] Ch. Routsi, J.K. Yakinthos and H. Gamari-Seale, J. Magn. Magn. Mater. I10 (1992) 317. [3] A.E. Dwight, W.C. Harper and C.W. Kimball, J. LessCommon Met. 30 (1973) 1. [4] K. Yvon, W. Jeitschko and E. Parthe, J. Appl. Crystallogr. 10 (1977) 73. [5] E. Hovestreydt, N. Engel, K. Klepp, B. Chabot and E. Parthe, J. Less-Common Met. 85 (1982) 247. [6] D. Rossi, R. Marazza and R. Ferro, J. Less-Common Met. 107 (1985) 99. [7] B. Leon and W.E. Wallace J. Less-Common Met. 22 (1970) 1. [8] J. Sakurai, Y. Yamaguchi, K. Mibu and T. Shinjo, J. Magn. Magn. Mater. 84 (1990) 157. [9] B. Buffat, B. Chevalier, M.H. Tuilier, B. Llotet and J. Etourneau, Solid State Commun. 49 (1986) 17.
Magnetic characteristics of some RNiSn (R = Ce, Pr, Nd, Sm) and RRhSn (R = Ce, Pr, Nd) compounds C h . D . R o u t s i , J.K. Y a k i n t h o s Democritos University of Thrace, Electrical Engineering Department, Physics Laboratory, 67100 Xanthi, Greece
and
H. G a m a r i - S e a l e Institute of Material Science, NSRC Democritos, 153.10Aghia ParaskeviAttiki, Greece
Received 24 April 1992
Magnetic properties of seven equiatomic ternary RNiSn and RRhSn compounds(R = light rare earth) have been studied in fields of up to 20 kOe in the temperature range 4.2-200 K. It has been found that all compoundsfollow the Curie-Weiss law above 40 K, except CeNiSn and CeRhSn which do not show Curie-Weiss behavior at any temperature. The latter show a Kondo or valence fluctuation behavior. The compound SmNiSn orders antiferromagneticallywith a N6el temperature = 9 K. No ordering temperature was observed down to 4.2 K for the rest of the compounds.
1. Introduction The compounds RNiSn and R R h S n with heavy R elements have already been studied in our previous papers [1,2]. The susceptibility of YTSn (T -- Ni, Rh) is temperature independent and the moment of nickel and rhodium was found to be zero in the whole series. In the nickel series the compounds with Gd, Th and Dy are antiferromagnetic at low temperatures while no ordering temperature was observed down to 4.2 K for the compounds with Ho, Er and Tm. The GdRhSn, ThRhSn and DyRhSn compounds order antiferromagnetically with N6el temperatures 14.8, 18.4 and 8 K respectively. TbRhSn presents a second small susceptibility maximum at 6.2 K, perhaps suggesting a change in the magnetic structure
Correspondence to: Dr. Ch.D. Routsi, Democritos University of Thrace, Electrical Engineering Department, Physics Laboratory, 67100 Xanthi, Greece.
within the ordered range. The H o R h S n and ErRhSn compounds do not show any magnetic ordering down to 4.2 K. The crystal structure of the R R h S n series with R -- heavy rare earth was determined by Dwight e t al. [3]. In this paper, a continuation of our systematic study of the RTSn (T = transition metal) equiatomic compounds, we determine the crystal structure of the R R h S n series with R = light rare earth and study its macroscopic magn e t i c p r o p e r t i e s as well as those of the RNiSn series, with R = Ce, Pr, Nd, Sm.
2. Experimental The preparation as well as the magnetic susceptibility measurement techniques of RTSn (T = Ni, Rh) are described in ref. [1]. The compounds were examined by X-ray analysis and were found to be single-phased. The compounds
0304-8853/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved
Ch.D. Routsi et al. / Characteristics of RNiSn and RRhSn compounds
80
CeRhSn, PrRhSn and NdRhSn were found to crystallize in a hexagonal unit cell with a and c parameters given in table 1. Using the LazyPulverix program [4], the best fit for the observed intensity of reflections in the RRhSn (R = Ce, Pr, Nd) series was achieved for the atom sites, of the hexagonal type FeEP crystal structure (space group P62m), given by Dwight et al. [3] and not those given by Hovestreydt et al. [5]. The compounds RNiSn were found to crystallize in the orthorhombic TiNiSi type (space group Pnma) and their lattice parameters are in good agreement with those determined by Rossi et al. [6].
J 70
o
PrNiSn NdNiSn
60
H=IKOe 80
40
3O
H = 2 0 0 Oe
3. Results and discussion
---.... 2 0
i 3.1. RNiSn compounds (R = Ce, Pr, Nd, Sm) lO
The reciprocal susceptibility vs. temperature for the RNiSn compounds is presented in figs. 1 and 2. PrNiSn follows a Curie-Weiss law from 30 K to the highest available temperature. From this part of the graph a negative paramagnetic Curie temperature (Op) is derived equal to - 1 0 K indicating that antiferromagnetic interactions are predominant. The experimental /.%el= 3.67/z a is found to be slightly greater than the theoretically calculated /.Lth=gj[J(J+ 1)] 1/2 for the free tripositive rare-earth ion. Similar results have been obtained for PrNiA1 [7] and for PrPtSn [2] which do not show any ordering down to 4.2 K either, with/xeff = 3.75/x a and @p = - 10 K (see table 2). NdNiSn exhibits Curie-Weiss behavior above 30 K and a/xeff equal to 4.2t~B which is also slightly larger than that of the tripositive ion. The compound does not show any ordering down to 4.2 K. SmNiSn orders antiferromagnetically, presenting
0
40
80
120
160
T(K)
Fig. 1. Reciprocal susceptibility vs. temperature of PrNiSn and NdNiSn compounds.
a susceptibility maximum at 9 K. There is a second very small maximum in the susceptibility below T N (at --- 5 K) which may correspond to a magnetic transition similar to that observed in SmPdSn compound [8]. A neutron diffraction study of TbNiSn, now in progress in our laboratory, shows that this compound also presents two different magnetic structures below T N. CeNiSn does not show Curie-Weiss behaviour at any temperature. The graph X -1 vs. T concaves downwards and the susceptibility values are much smaller than those expected from the Curie law.
Table 1 Lattice constants of RRhSn (R = Ce, Pr, Nd) compounds with the FezP-type structure and atomic positions for PrRhSn Compound
a (,A)
c (,~)
Atom
Position
x
y
z
CeRhSn PrRhSn NdRhSn
7.55 7.539 7.53
3.97 3.92 3.89
Pr Sn Rh I Rh n
3(8) 3(f) l(b) 2(c)
x x 0 ½
0 0 0 ~
½ 0
Xpr = 0.605, Xs, = 0.265.
1
0
Ch.D. Routsi et al. / Characteristics of RNiSn and RRhSn compounds
•
CeNiln
•
ImNilln
81
2.30
16(
•00
120
•OO
E = 1.0o E
400
SO
FI
1.711 40
200
/ / /
0
/
o
4~
i • 4TIK)
.'o
i
i
12
16
' =
1~0
160
I
1.50 0.30
T(K)
2.00
iogT(K)
F i g . 3.
Reciprocal susceptibility vs. temperature under 1 kOe of CeNiSn and SmNiSn compounds (insert: susceptibility variation at low temperatures of SmNiSn compound). F i g . 2.
The influence of the crystal field or spin compensation by the conduction electrons (Kondo phenomenon), or both, may be responsible. Similar behavior was observed in CeNiAI [7]. The data in fig. 3 show that the measured inverse susceptibility X- 1 is linear with T °'3 suggesting that CeNiSn is a Kondo system. Leon et al. [7] found a T °'57 dependence of X - 1 for the CeNiAI compound. The isotherms of all compounds at ~ 4.5 K are straight lines passing from the origin (fig. 4).
1.50
1.00
0
Log-log plot of X - 1 fit y =
VS.
temperature for CeNiSn. Best
0 . 3 x + 1.65.
Curie-Weiss law above 40 K (fig. 5) approximately. Their paramagnetic Curie temperatures are + 10 and + 12 K respectively. In the paramagnetic region, their effective magnetic moments /Zeff are found to be in good agreement with the theoretical ~th for Pr 3+ and N d 3+. Down to 4.2 K the compounds do not show any ordering. No Curie-Weiss behavior is observed for CeRhSn (fig. 5). The dependence of the inverse
2oo I •
3.2. RRhSn compounds (R = Ce, Pr, Nd)
CeNiSn
/
o PrNiSn
o .,.,s.
The reciprocal susceptibility vs. temperature of the PrRhSn and NdNhSn compounds follows the Table
/
• SmNiSn
"
#
2
and the N~el temperature of the RNiSn and compounds
Compound
/'/'off
gJ[J(J + 1)] x/2
CeNiSn
-
2.56
-
-
PrNiSn NdNiSn
3.67 4.2
3.62 3.68
- 10 - 4
-
Op
T N (K)
SmNiSn
1.37
1.55
- 40
9
CeRhSn
-
2.56
-
-
PrRhSn
3.83
3.62
+ 10
-
NdRhSn
3.55
3.68
+ 12
-
-~
/
j
T,4.0 K 120 AX e
/zeff, /~t,, @p RRhSn
100
T,4.1B K
0
E
T,4.2K
"~'ao E e
I 40
0
4
•
12
16
20
HIKOe)
F i g . 4.
Magnetization vs. applied field at compounds.
4.5 K
of the
RNiSn
Ch.D. Routsi et al. / Characteristics of RNiSn and RRhSn compounds
82
60
•
CeRhSn
•
NdRhSn
susceptibility on temperature of CeRhSn is similar to that of CeNiSn suggesting a Kondo state or valence fluctuation. The slope of the variation of X-1 vs. T of CeRhSn is more pronounced than that of CeNiSn. The sharp increase of X is attributed, after Buffat et al. [9] to small amounts of stable C e 3 + ions stabilized by lattice defects or to traces of other magnetic rare earth ions. Isotherms of CeRhSn, PrRhSn and NdRhSn are shown in fig. 6. The magnetization of the Nd compound shows saturation at 4.2 K under a field of 4 kOe suggesting a ferromagnetic behavior. For all the RNiSn and RRhSn compounds, the values of the magnetic moments at 4.5 K under 20 kOe are much smaller than gjJ for the R 3+ free ion, indicating that saturation was not reached.
PrRhSn
50
40
160
30
120
20
BO
l) D 0
E v
L,
10
40
Y 0
40
80
120
0
References
T(K)
Fig. 5. Reciprocal susceptibility vs. temperature at 1 kOe of RRhSn with R = Ce, Pr, Nd. CeRhSn Pr RhSn • NdRhSn • /
~
/ /
lol-
,/ -"~ T : 4 . 6 K
'il / [1
/
,o
/
~
2
0
200
p
T:IoaK
"--'"
4
8
x10-1
1'2
40
16
20
0
H(KOe)
Fig. 6. Magnetization vs. applied field of RRhSn with R = Ce, Pr, Nd.
[1] Ch. Routsi, J.K. Yakinthos and H. Gamari-Seale, J. Magn. Magn. Mater. 98 (1991) 257. [2] Ch. Routsi, J.K. Yakinthos and H. Gamari-Seale, J. Magn. Magn. Mater. I10 (1992) 317. [3] A.E. Dwight, W.C. Harper and C.W. Kimball, J. LessCommon Met. 30 (1973) 1. [4] K. Yvon, W. Jeitschko and E. Parthe, J. Appl. Crystallogr. 10 (1977) 73. [5] E. Hovestreydt, N. Engel, K. Klepp, B. Chabot and E. Parthe, J. Less-Common Met. 85 (1982) 247. [6] D. Rossi, R. Marazza and R. Ferro, J. Less-Common Met. 107 (1985) 99. [7] B. Leon and W.E. Wallace J. Less-Common Met. 22 (1970) 1. [8] J. Sakurai, Y. Yamaguchi, K. Mibu and T. Shinjo, J. Magn. Magn. Mater. 84 (1990) 157. [9] B. Buffat, B. Chevalier, M.H. Tuilier, B. Llotet and J. Etourneau, Solid State Commun. 49 (1986) 17.