- Email: [email protected]
Magnetic properties of RE2Ni3Si5 (RE Nd, Tb and Dy)
Journal of Magnetism and Magnetic Materials 140-144 (1995) 917-918
journal of magnetism and magnelic materials
ELSEVIER
Magnetic properties of RE2Ni3Si 5 (RE = Nd, Tb and Dy) Chandan Mazumdar b R. Nagarajan a,* L.C. Gupta a B.D. Padalia b R. Vijayaraghavan a Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Bombay 400 005, India b Department of Physics, Indian Institute of Technology, Bombay 400 076, India
Abstract Magnetic properties of Dy2Ni3Si 5 and the two new materials Nd2Ni3Si 5 and TbeNi3Si 5 are presented. Both Nd2Ni3Si 5 and Dy2Ni3Si 5 order antiferromagnetically with T N = 9.5 K. Tb2Ni3Si 5 shows two distinct magnetic transitions at T m = 19.5 K and at TN2 = 12 K. In the paramagnetic state, all these materials exhibit Curie-Weiss behaviour.
Several members of the series RE2Ni3Si 5 (RE = Y, rare earth), viz., Ce2Ni3Si 5 and Eu2Ni3Si 5, exhibit valence fluctuation (VF) properties [1,2]. RE2Ni3Si 5 (RE = Pr, Sm, Gd and He), reported earlier, order antiferromagnetically at ~ 8.5, ~ 11, ~ 15 and ~ 6 K respectively [3,4]. The value of these T N's do not follow the de Gennes scaling (1, 0.051, 0.283, 0.386 for Gd, Pr, Sm, He respectively). Thus it was considered essential to study magnetic properties of other members of this series. Here, we describe the synthesis of two new compounds Nd2Ni3Si 5 and Tb2Ni3Si 5 and their magnetic properties. We also report here magnetic properties of Dy2Ni3Si 5, synthesis of which has been reported earlier [5]. Nd2Ni3Sis, Tb2Ni3Si s and Dy2Ni3Si 5 were prepared by standard arc melting technique. The samples were vacuum annealed at l l 0 0 ° C for 1 d, at 1000°C for 7 d and cooled slowly to room temperature. X-ray powder diffraction (XRD) pattern of the resulting polycrystalline samples were measured (Jeol, Japan), using Cu K a radiation. Magnetic susceptibility ( X ) measurements were carried out on a Faraday type susceptometer (George Associates, USA) in the temperature range 5 - 3 0 0 K and on a SQUID magnetometer (Quantum Design Inc., USA) in the temperature range 2 - 3 0 0 K. In the susceptibility measurements, the samples were cooled in zero applied magnetic field, then the magnetic field (4 kG) was applied and the data were taken in the warming cycle. Room temperature powder XRD patterns (Fig. 1) of Nd2Ni3Sis, TbzNi3Si 5 and Dy2Ni3Si 5 show that they are single phase materials, conforming to the orthorhombic U2Co3Sis-type structure (space group Ibam) similar to
* Corresponding author. [email protected].
Fax:
+91-22-215 2110; email:
DyzN[3Si 5
m
Tb E N[3 Si 5
0~
tO
20
30
40 20
50
60
1
I
'70
(degree)
Fig. 1. Powder X-ray diffraction pattern of Nd 2Ni3Sis, Tb2 Ni3Si5 and Dy2Ni3Si 5 at room temperature using Cu K a radiation. some other compounds already known in the series RE2Ni3Si 5 [1-4]. Lattice cell parameters, determined from the line positions of the XRD pattern, using a least squares fit procedure, are shown in Table 1. Their lattice parameters, along with the lattice parameters of other members of Table 1 Structural and magnetic properties of RE2Ni3Si ~ (RE = Nd, Tb and Dy) Nd2Ni3Si 5 Tb2Ni3Si 5 Dy2Ni3Si 5 Dy2Ni3Si5 a (A) b (A) c (A) /Xeff / R E 090 (K) TN (K)
9.627 11.356 5.731 3.74 - 14.3 9.5
9.552 11.156 5.648 9.9 8.0 19.5, 12 b
9.547 11.115 5.633 10.8 5.8 9.5
a From Ref. [5]. b There are two magnetic transitions in Tb2Ni3Si 5.
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0 3 0 4 - 8 8 5 3 ( 9 4 ) 0 0 7 3 7 - 3
9.544 a 11.116 a 5.633 a
C. Mazumdar et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 917-918
918
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qo2~
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= 05 ;
~0.1
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100
800
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=
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300
h,.
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~o
e
I
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o
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_ / /
1O0
Field 4 K G a u s . ~
&pp]ied
_
200
Tetzlperature
(K)
Fig. 2. The dc magnetic susceptibility and its inverse of Nd2Ni3Si 5 measured in a field of 4 kG. The solid line is a fit to the Curie-Weiss law. The inset shows the expanded region near magnetic ordering temperature.
the series RE2Ni3Si 5 [1-4], follow the usual lanthanide contraction (except for Ce2Ni3Si 5 and Eu2Ni3Si 5 which are VF systems). Results of our susceptibility measurements of RE2Ni3Si5, RE = Nd, Tb and Dy, are shown in Figs. 2, 3 and 4. Inverse susceptibility, X -1, in each case, exhibits a linear temperature dependence in the high temperature range. The values of effective magnetic moment /&ff and paramagnetic Curie-Weiss (CW) temperature Op obtained from a CW fit to X-a, for all the compounds, are given in Table 1. The values of /Zeff, in each case, is close to, but slightly higher than, that of the trivalent free rare earth ion. In this structure, the 3d metal is not expected to carry a magnetic moment. However, our measurements on the non-magnetic rare earth analogue, YzNi3Si 5 [1], showed a small magnetic moment. An interesting possibility is that of Ni carrying a small moment in these materials. This aspect needs further investigations. Below ~ 30 K, x ( T ) of Nd2Ni3Si 5 (Fig. 2) is slightly higher than the CW value, x ( T ) behaviour at low temperature is similar to an antiferromagnetic transition and exhibits a maximum at 9.5 K. We point out here that, considering that TN of the Gd analogue is ~ 15 K, de Gennes scaling suggests that T N of Nd2Ni3Si 5 should have been ~ 1.7 K. The observed T N (9.5 K) is anoma-
5
.-
T ~..
300
(K)
Fig. 4. The dc magnetic susceptibility and its inverse of DysNi3Si 5 measured in a field of 4 kG. The solid line is a fit to the Curie-Wiess law. The inset show the expanded region near magnetic ordering temperature. lous as it is about five times of that expected from de Gennes scaling. x ( T ) of Tb2Ni3Si 5 is shown in Fig. 3. Deviation of the inverse susceptibility of the material from a CW behaviour below ~ 80 K may be because of the crystal field effect. Interestingly, the material exhibits two magnetic transitions at TN1 = 19.5 K and TN2 = 12 K. The lower transition temperature follows de Gennes scaling. It is quite conceivable that the two transitions may correspond to an incommensurate (19.5 K) ~ commensurate (12 K) magnetic ordering of Tb spins. Neutron diffraction and specific heat studies of this material are underway. x ( T ) of DY2Ni3Si 5 is shown in Fig. 4. In this case the deviation from CW occurs below 60 K which, in this case also, may possibly be due to crystal field effects. The peak in x ( T ) suggests that the material orders antiferromagnetically around 9.5 K. In summary, Nd2Ni3Si5, Tb2Ni3Si 5 and Dy2Ni3Si 5 order antiferromagnetically. A double magnetic transition is observed in Tb2Ni3Si 5. All the compounds show a CW behaviour at high temperatures. The magnetic moment per rare earth ion in all the three compounds is close to, but somewhat higher than, that of respective free trivalent rare earth ions. This may imply existense of a small moment on Ni in these compounds [1]. References
~" 1.0 o 0.8
12 T 10 C
~0.6
8
~--
6
~
OI4
4
=
0.2
2
~
,.~ o.o
o
=
0
100
200
Temperature
300
(X)
Fig. 3. The dc magnetic susceptibility and its inverse of Th2 Ni3 Si5 measured in a field of 4 kG. The solid line is a fit to the Curie-Weiss law. The inset shows the expanded region of susceptibility near the two ordering temperatures.
[1] Chandan Mazumdar, R. Nagarajan, S.K. Dhar, L.C. Gupta, R. Vijayaraghavan and B.D. Padalia, Phys. Rev. B 46 (1992) 9009. [2] Sujata Patil, R. Nagarajan, L.C. Gupta, C. Godart, R. Vijayaraghavan and B.D. Padalia, Phys. Rev. B 37 (1988) 7708. [3] Chandan Mazumdar, R. Nagarajan, L.C. Gupta, R. Vijayaraghavan, C. Godart and B.D. Padalia, J. Appl. Phys. 75 (1994) 7155. [4] Chandan Mazumdar, R. Nagarajan, L.C. Gupta, R. Vijayaraghavan, C. Godart and B.D. Padalia, IEEE Trans. Magn., in press. [5] B. Chabot and E. Parthe, J. Less-Common Met. 97 (1984) 285.
journal of magnetism and magnelic materials
ELSEVIER
Magnetic properties of RE2Ni3Si 5 (RE = Nd, Tb and Dy) Chandan Mazumdar b R. Nagarajan a,* L.C. Gupta a B.D. Padalia b R. Vijayaraghavan a Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Bombay 400 005, India b Department of Physics, Indian Institute of Technology, Bombay 400 076, India
Abstract Magnetic properties of Dy2Ni3Si 5 and the two new materials Nd2Ni3Si 5 and TbeNi3Si 5 are presented. Both Nd2Ni3Si 5 and Dy2Ni3Si 5 order antiferromagnetically with T N = 9.5 K. Tb2Ni3Si 5 shows two distinct magnetic transitions at T m = 19.5 K and at TN2 = 12 K. In the paramagnetic state, all these materials exhibit Curie-Weiss behaviour.
Several members of the series RE2Ni3Si 5 (RE = Y, rare earth), viz., Ce2Ni3Si 5 and Eu2Ni3Si 5, exhibit valence fluctuation (VF) properties [1,2]. RE2Ni3Si 5 (RE = Pr, Sm, Gd and He), reported earlier, order antiferromagnetically at ~ 8.5, ~ 11, ~ 15 and ~ 6 K respectively [3,4]. The value of these T N's do not follow the de Gennes scaling (1, 0.051, 0.283, 0.386 for Gd, Pr, Sm, He respectively). Thus it was considered essential to study magnetic properties of other members of this series. Here, we describe the synthesis of two new compounds Nd2Ni3Si 5 and Tb2Ni3Si 5 and their magnetic properties. We also report here magnetic properties of Dy2Ni3Si 5, synthesis of which has been reported earlier [5]. Nd2Ni3Sis, Tb2Ni3Si s and Dy2Ni3Si 5 were prepared by standard arc melting technique. The samples were vacuum annealed at l l 0 0 ° C for 1 d, at 1000°C for 7 d and cooled slowly to room temperature. X-ray powder diffraction (XRD) pattern of the resulting polycrystalline samples were measured (Jeol, Japan), using Cu K a radiation. Magnetic susceptibility ( X ) measurements were carried out on a Faraday type susceptometer (George Associates, USA) in the temperature range 5 - 3 0 0 K and on a SQUID magnetometer (Quantum Design Inc., USA) in the temperature range 2 - 3 0 0 K. In the susceptibility measurements, the samples were cooled in zero applied magnetic field, then the magnetic field (4 kG) was applied and the data were taken in the warming cycle. Room temperature powder XRD patterns (Fig. 1) of Nd2Ni3Sis, TbzNi3Si 5 and Dy2Ni3Si 5 show that they are single phase materials, conforming to the orthorhombic U2Co3Sis-type structure (space group Ibam) similar to
* Corresponding author. [email protected].
Fax:
+91-22-215 2110; email:
DyzN[3Si 5
m
Tb E N[3 Si 5
0~
tO
20
30
40 20
50
60
1
I
'70
(degree)
Fig. 1. Powder X-ray diffraction pattern of Nd 2Ni3Sis, Tb2 Ni3Si5 and Dy2Ni3Si 5 at room temperature using Cu K a radiation. some other compounds already known in the series RE2Ni3Si 5 [1-4]. Lattice cell parameters, determined from the line positions of the XRD pattern, using a least squares fit procedure, are shown in Table 1. Their lattice parameters, along with the lattice parameters of other members of Table 1 Structural and magnetic properties of RE2Ni3Si ~ (RE = Nd, Tb and Dy) Nd2Ni3Si 5 Tb2Ni3Si 5 Dy2Ni3Si 5 Dy2Ni3Si5 a (A) b (A) c (A) /Xeff / R E 090 (K) TN (K)
9.627 11.356 5.731 3.74 - 14.3 9.5
9.552 11.156 5.648 9.9 8.0 19.5, 12 b
9.547 11.115 5.633 10.8 5.8 9.5
a From Ref. [5]. b There are two magnetic transitions in Tb2Ni3Si 5.
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0 3 0 4 - 8 8 5 3 ( 9 4 ) 0 0 7 3 7 - 3
9.544 a 11.116 a 5.633 a
C. Mazumdar et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 917-918
918
_
-
o
J
2 0
10
o 03 Oo E ©
°
:'~
)
qo2~
75 k
0.2
°
< 1 0 (1)
= 05 ;
~0.1
0
0.0 0
100
800
'Pernperature
=
0
300
h,.
<
~o
e
I
""
]i
...~ . .,. . . .
20 -
o
(K)
o.. - ~ /
a{)~/'~ DY2NiLsS'i5
_ / /
1O0
Field 4 K G a u s . ~
&pp]ied
_
200
Tetzlperature
(K)
Fig. 2. The dc magnetic susceptibility and its inverse of Nd2Ni3Si 5 measured in a field of 4 kG. The solid line is a fit to the Curie-Weiss law. The inset shows the expanded region near magnetic ordering temperature.
the series RE2Ni3Si 5 [1-4], follow the usual lanthanide contraction (except for Ce2Ni3Si 5 and Eu2Ni3Si 5 which are VF systems). Results of our susceptibility measurements of RE2Ni3Si5, RE = Nd, Tb and Dy, are shown in Figs. 2, 3 and 4. Inverse susceptibility, X -1, in each case, exhibits a linear temperature dependence in the high temperature range. The values of effective magnetic moment /&ff and paramagnetic Curie-Weiss (CW) temperature Op obtained from a CW fit to X-a, for all the compounds, are given in Table 1. The values of /Zeff, in each case, is close to, but slightly higher than, that of the trivalent free rare earth ion. In this structure, the 3d metal is not expected to carry a magnetic moment. However, our measurements on the non-magnetic rare earth analogue, YzNi3Si 5 [1], showed a small magnetic moment. An interesting possibility is that of Ni carrying a small moment in these materials. This aspect needs further investigations. Below ~ 30 K, x ( T ) of Nd2Ni3Si 5 (Fig. 2) is slightly higher than the CW value, x ( T ) behaviour at low temperature is similar to an antiferromagnetic transition and exhibits a maximum at 9.5 K. We point out here that, considering that TN of the Gd analogue is ~ 15 K, de Gennes scaling suggests that T N of Nd2Ni3Si 5 should have been ~ 1.7 K. The observed T N (9.5 K) is anoma-
5
.-
T ~..
300
(K)
Fig. 4. The dc magnetic susceptibility and its inverse of DysNi3Si 5 measured in a field of 4 kG. The solid line is a fit to the Curie-Wiess law. The inset show the expanded region near magnetic ordering temperature. lous as it is about five times of that expected from de Gennes scaling. x ( T ) of Tb2Ni3Si 5 is shown in Fig. 3. Deviation of the inverse susceptibility of the material from a CW behaviour below ~ 80 K may be because of the crystal field effect. Interestingly, the material exhibits two magnetic transitions at TN1 = 19.5 K and TN2 = 12 K. The lower transition temperature follows de Gennes scaling. It is quite conceivable that the two transitions may correspond to an incommensurate (19.5 K) ~ commensurate (12 K) magnetic ordering of Tb spins. Neutron diffraction and specific heat studies of this material are underway. x ( T ) of DY2Ni3Si 5 is shown in Fig. 4. In this case the deviation from CW occurs below 60 K which, in this case also, may possibly be due to crystal field effects. The peak in x ( T ) suggests that the material orders antiferromagnetically around 9.5 K. In summary, Nd2Ni3Si5, Tb2Ni3Si 5 and Dy2Ni3Si 5 order antiferromagnetically. A double magnetic transition is observed in Tb2Ni3Si 5. All the compounds show a CW behaviour at high temperatures. The magnetic moment per rare earth ion in all the three compounds is close to, but somewhat higher than, that of respective free trivalent rare earth ions. This may imply existense of a small moment on Ni in these compounds [1]. References
~" 1.0 o 0.8
12 T 10 C
~0.6
8
~--
6
~
OI4
4
=
0.2
2
~
,.~ o.o
o
=
0
100
200
Temperature
300
(X)
Fig. 3. The dc magnetic susceptibility and its inverse of Th2 Ni3 Si5 measured in a field of 4 kG. The solid line is a fit to the Curie-Weiss law. The inset shows the expanded region of susceptibility near the two ordering temperatures.
[1] Chandan Mazumdar, R. Nagarajan, S.K. Dhar, L.C. Gupta, R. Vijayaraghavan and B.D. Padalia, Phys. Rev. B 46 (1992) 9009. [2] Sujata Patil, R. Nagarajan, L.C. Gupta, C. Godart, R. Vijayaraghavan and B.D. Padalia, Phys. Rev. B 37 (1988) 7708. [3] Chandan Mazumdar, R. Nagarajan, L.C. Gupta, R. Vijayaraghavan, C. Godart and B.D. Padalia, J. Appl. Phys. 75 (1994) 7155. [4] Chandan Mazumdar, R. Nagarajan, L.C. Gupta, R. Vijayaraghavan, C. Godart and B.D. Padalia, IEEE Trans. Magn., in press. [5] B. Chabot and E. Parthe, J. Less-Common Met. 97 (1984) 285.