- Email: [email protected]
Comparative study of the doping effects in NdNiO3 by transition metals (Fe, Co, Cu)
Journal of Magnetism and Magnetic Materials 140-144 (1995) 2155-2156
Journal of magnetism and magnetic materials
ELSEVIER
Comparative study of the doping effects in NdNiO 3 by transition metals (Fe, Co, Cu) J. Blasco *, J. Garcla 1CMA, CSIC - Universidad de Zaragoza, 50009 Zaragoza, Spain
Abstract Nickel has been partially replaced by other transition metals (Fe, Co, Cu) in the NdNiO 3 perovskite. Magnetic and electrical measurements have been performed between 4.2 and 300 K in heating and cooling runs. The undoped NdNiO 3 sample shows a metal-insulator transition (MI) at 205 K with a large thermal hysteresis. The substitution of Ni by Cu leads to metallic behaviour in the whole temperature range with an increase in the Pauli paramagnetism while the replacement of Ni by Fe or Co leads to semiconducting samples.
The 3d transition metal oxides with perovskite structure have been studied extensively [1]. Recently there is a renewed interest in the study of RENiO 3 compounds and related systems due to their metal-insulator (MI) phase transition and structural relationship with high-T~ superconductors [2-5]. The metallic or insulator behaviour in these compounds depends strongly on the distortion degree of the ideal cubic perovskite structure and is related to the N i - O - N i bond angle. Moreover, antiferromagnetic ordering occurs simultaneously to the MI transition in NdNiO 3 and PrNiO 3 [4]. Substitution of Ni in the lattice may clarify the origin of the MI phase transition on NdNiO 3. Therefore, the neighbour metals iron, cobalt and copper were chosen. These substitutions could enable to distinguish between the electronic localization and magnetic ordering of the Ni sublattice. Following the Torrance classification for oxides [6], the substitution of Ni by Fe or Co would induce an electronic localization resulting in a non-metallic state while the replacement by Cu would produce metallic compounds. The samples used in this work were characterized by means of X-ray powder diffraction. Iron and cobalt substitutions show single phase diffraction patterns with an orthorhombic unit cell similar to that of NdNiO 3. The unit cell volume of NdNil_~FexO 3 increases with the iron content, while for NdNil_xCoxO 3 samples, it decreases with the Co content. Substitution by Cu is only possible up to x < 0.15 (orthorhombic cell). X-ray patterns of NdNil_xCU/O 3 samples with x > 0.2 show additional phases as NiO and Nd2MO 4 (M = Cu or Ni).
* Corresponding [email protected].
author.
Fax:
+ 34-76-553773;
email:
1041o
4.4
104 .
4.0
r~io 3..............
o 104. ~ ×
NdNi..Fe. ,O~ aD~ NdNi0.gCo0.tO3 ,L,o~o o o NdNio.gCu0.103 ~ 0o × ~r~ D 0 × × × ~%o ° ×××× £t~o o o x X × x
~ 3.6 1 0 4 .
"~ 3.2 104" 2.8
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300
T (K) Fig. 1. AC magnetic susceptibility of NdNi 1_xMxO3 (M = Cu, Fe or Co) samples.
The ac magnetic susceptibility from 4.2 up to 300 K were determined using an ac susceptometer. 1 / X vs. T curves for x = 0.1 samples and NdNiO 3 are shown in Fig. 1. All samples show a Curie-Weiss-like behaviour which deviates from linearity at temperatures lower than 80 K due to the Nd 3÷ free ion crystal field splitting. The data Table 1 Magnetic parameters C, 0, X0 and calculated p,,ff of NdNil_xMxO 3 samples (M x = Cu, Fe or Co, given in the table) Sample
C (× 10-3 emu K/g)
0 (K)
X0 (X 10-6 emu/g)
~lLeff( /.LB)
NdNiO 3 Cu0.05 Cu0A Cu0.15 Fe0. I Fe0.3 Co0.1 Co0.3
6.38 5.7 5.7 5.85 6.48 8.02 5.6 5.24
- 53 - 42 -40 - 40 - 47 - 55 -41 - 23
3.87 5.3 10 6.2 4.58 5.41 5.2 6.1
3.57 3.41 3.41 3.47 3.59 4.0 3.37 3.25
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 1 1 2 5 - 7
4.8
J. Blasco, J. Garcla/Journal of Magnetism and Magnetic Materials 140-144 (1995) 2155-2156
2156
loOi ....
10-
i ....
J
.
.
.
.
, ....
i...,I,,,,
~
~ 10-3
.... 0
e o ~
~ .... ~ .... ~ .... ~ .... ~ .... 50 100 150 200 250 300
T (K) Fig. 2. AC resistivity vs. temperature of NdNiO 3 ( ), NdNi0.95Coo.0503 (×), NdNi0.9Co0AO3 (~), NdNi0.7Coo.303 (D), NdNi0.95Feo.0503 (O), NdNi 0 .9Fe0.103 ( + ) , NdNio.7Fe0.303 ( A ), NdNi0.95Cu0.osO3 ( • ) , NdNi0.85Cu0.1503
(o). above 100 K have been fitted to the equation X = Xo + C / ( T - 0). This expression includes a Curie-Weiss term and a temperature-independent parameter (Xo) to take into account further magnetic contributions as Pauli paramagnetism and core diamagnetism. All samples show similar magnetic constants (see Table 1) with a Curie-Weiss contribution mainly coming from the Nd sublattice (theoretical Nd 3+ magnetic moment is 3.67/z B) and Pauli paramagnetism of a similar value as for LaNiO 3 [5]. NdNil_xCUxO 3 samples show an increase of the Xo parameter, the Curie-Weiss contribution remaining constant. On the other hand, in NdNia_xFexO 3 samples, the increase of effective moments can be related to the paramagnetic contribution of the high-spin Fe 3+ ion. In NdNil_xCOxO 3 samples, the effective magnetic moments calculated are similar to NdNiO3, in agreement with previous works that reported on Co 3+ in low spin state at low temperatures [7]. It is important to note that no S = i Ni3+ contribution has been specifically detected in all samples and no magnetic anomalies have been found in the whole temperature range. The temperature dependence of the resistivity between 4.2 and 300 K is shown in Fig. 2. NdNiO 3 is characterized by an MI phase transition at 205 K with a large thermal hysteresis [5]. The main effect of Ni substitution is the temperature decrease or disappearance of the MI phase transition. NdNil_xMxO 3 (M = Fe, Co or Cu) samples with x = 0.05 show a decrease of the MI phase transition
from 205 down to 120 and 130 K for Fe and Co substitutions respectively, and the disappearance for Cu substitution. For x = 0.1 samples, the MI phase transition with thermal hysteresis has disappeared in all samples. Substitution by Cu gives metallic samples, and by Co or Fe yields samples with, practically, temperature-independent behaviour. In the case of Co sample, it shows a positive slope from 300 down to 50 K (metallic) and negative at lower temperatures. For Fe compound the slope is practically negative (semiconductor) in the whole temperature range. For higher Fe or Co content, the samples are semiconducting. In a general way, the effects of Ni substitution are in agreement with the Torrance classification [6], hence increasing the substitution by Fe or Co increases the insulator character of the samples, while Cu substitution increases the metallic behaviour. On the other hand, low percentages of substitution by the three different atoms induce the same effect on the MI phase transition. These results indicate that a simple mechanism of a band gap, i.e. increase of the electronic density due to the replacement of Ni by Cu or decrease in the number of states at the Fermi level due to the more localized Fe 3+ or Co 3+ states, may explain the general electrical behaviour but cannot explain the stabilization of metallic phase in all cases for low percentages of substitution and the suppression of the MI phase transition. This suppression is not well understood in the frame of the current theories and some other mechanisms will be responsible for this phase transition. Furthermore, the absence of magnetic anomaly at the MI transition suggests large magnetic correlations in the high temperature phase. An explanation to the behaviour at low percentages of substitution could be the change of the electronic states responsible for the conductivity properties due to the occupational disorder induced by substitution. It has been proposed that there is a characteristic spin density wave ordering at the NdNiO 3 phase transition [4]. The disorder induced by low percentages of substitution may break the phase coherence for the localization of the spin density wave resulting in an increase of the metallic range. Acknowledgement: This work has been supported by CICYT MAT93-0240-C04-04 and PB92-1077 projects. References
[1] [2] [3] [4] [5] [6] [7]
J.B. Goodenough, Prog. Solid State Chem. 5 (1972) 145. J.K. Vassiliou et al., J. Solid State Chem. 81 (1989) 208. J.B. Torrance et al., Phys. Rev. B 45 (14) (1992) 8209. J.L. Garcia-Mufioz et al., Europhys. Lett. 20 (3) (1992) 241. J. Blasco et al., J. Phys: Condens. Matter 6 (1994) 5875. J.B. Torrance et al., Physica C 182 (1991) 351. D.S. Rajoria et al., J.C.S. Faraday II 70 (1974) 512.
Journal of magnetism and magnetic materials
ELSEVIER
Comparative study of the doping effects in NdNiO 3 by transition metals (Fe, Co, Cu) J. Blasco *, J. Garcla 1CMA, CSIC - Universidad de Zaragoza, 50009 Zaragoza, Spain
Abstract Nickel has been partially replaced by other transition metals (Fe, Co, Cu) in the NdNiO 3 perovskite. Magnetic and electrical measurements have been performed between 4.2 and 300 K in heating and cooling runs. The undoped NdNiO 3 sample shows a metal-insulator transition (MI) at 205 K with a large thermal hysteresis. The substitution of Ni by Cu leads to metallic behaviour in the whole temperature range with an increase in the Pauli paramagnetism while the replacement of Ni by Fe or Co leads to semiconducting samples.
The 3d transition metal oxides with perovskite structure have been studied extensively [1]. Recently there is a renewed interest in the study of RENiO 3 compounds and related systems due to their metal-insulator (MI) phase transition and structural relationship with high-T~ superconductors [2-5]. The metallic or insulator behaviour in these compounds depends strongly on the distortion degree of the ideal cubic perovskite structure and is related to the N i - O - N i bond angle. Moreover, antiferromagnetic ordering occurs simultaneously to the MI transition in NdNiO 3 and PrNiO 3 [4]. Substitution of Ni in the lattice may clarify the origin of the MI phase transition on NdNiO 3. Therefore, the neighbour metals iron, cobalt and copper were chosen. These substitutions could enable to distinguish between the electronic localization and magnetic ordering of the Ni sublattice. Following the Torrance classification for oxides [6], the substitution of Ni by Fe or Co would induce an electronic localization resulting in a non-metallic state while the replacement by Cu would produce metallic compounds. The samples used in this work were characterized by means of X-ray powder diffraction. Iron and cobalt substitutions show single phase diffraction patterns with an orthorhombic unit cell similar to that of NdNiO 3. The unit cell volume of NdNil_~FexO 3 increases with the iron content, while for NdNil_xCoxO 3 samples, it decreases with the Co content. Substitution by Cu is only possible up to x < 0.15 (orthorhombic cell). X-ray patterns of NdNil_xCU/O 3 samples with x > 0.2 show additional phases as NiO and Nd2MO 4 (M = Cu or Ni).
* Corresponding [email protected].
author.
Fax:
+ 34-76-553773;
email:
1041o
4.4
104 .
4.0
r~io 3..............
o 104. ~ ×
NdNi..Fe. ,O~ aD~ NdNi0.gCo0.tO3 ,L,o~o o o NdNio.gCu0.103 ~ 0o × ~r~ D 0 × × × ~%o ° ×××× £t~o o o x X × x
~ 3.6 1 0 4 .
"~ 3.2 104" 2.8
104"
DODOQOO x × × x x
2.4 2.0
104-
1.6
104
•
•
100
.
i
.
.
,
140
i 180
,
.
.
i
•
•
.
220
,
.
.
,
260
300
T (K) Fig. 1. AC magnetic susceptibility of NdNi 1_xMxO3 (M = Cu, Fe or Co) samples.
The ac magnetic susceptibility from 4.2 up to 300 K were determined using an ac susceptometer. 1 / X vs. T curves for x = 0.1 samples and NdNiO 3 are shown in Fig. 1. All samples show a Curie-Weiss-like behaviour which deviates from linearity at temperatures lower than 80 K due to the Nd 3÷ free ion crystal field splitting. The data Table 1 Magnetic parameters C, 0, X0 and calculated p,,ff of NdNil_xMxO 3 samples (M x = Cu, Fe or Co, given in the table) Sample
C (× 10-3 emu K/g)
0 (K)
X0 (X 10-6 emu/g)
~lLeff( /.LB)
NdNiO 3 Cu0.05 Cu0A Cu0.15 Fe0. I Fe0.3 Co0.1 Co0.3
6.38 5.7 5.7 5.85 6.48 8.02 5.6 5.24
- 53 - 42 -40 - 40 - 47 - 55 -41 - 23
3.87 5.3 10 6.2 4.58 5.41 5.2 6.1
3.57 3.41 3.41 3.47 3.59 4.0 3.37 3.25
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 1 1 2 5 - 7
4.8
J. Blasco, J. Garcla/Journal of Magnetism and Magnetic Materials 140-144 (1995) 2155-2156
2156
loOi ....
10-
i ....
J
.
.
.
.
, ....
i...,I,,,,
~
~ 10-3
.... 0
e o ~
~ .... ~ .... ~ .... ~ .... ~ .... 50 100 150 200 250 300
T (K) Fig. 2. AC resistivity vs. temperature of NdNiO 3 ( ), NdNi0.95Coo.0503 (×), NdNi0.9Co0AO3 (~), NdNi0.7Coo.303 (D), NdNi0.95Feo.0503 (O), NdNi 0 .9Fe0.103 ( + ) , NdNio.7Fe0.303 ( A ), NdNi0.95Cu0.osO3 ( • ) , NdNi0.85Cu0.1503
(o). above 100 K have been fitted to the equation X = Xo + C / ( T - 0). This expression includes a Curie-Weiss term and a temperature-independent parameter (Xo) to take into account further magnetic contributions as Pauli paramagnetism and core diamagnetism. All samples show similar magnetic constants (see Table 1) with a Curie-Weiss contribution mainly coming from the Nd sublattice (theoretical Nd 3+ magnetic moment is 3.67/z B) and Pauli paramagnetism of a similar value as for LaNiO 3 [5]. NdNil_xCUxO 3 samples show an increase of the Xo parameter, the Curie-Weiss contribution remaining constant. On the other hand, in NdNia_xFexO 3 samples, the increase of effective moments can be related to the paramagnetic contribution of the high-spin Fe 3+ ion. In NdNil_xCOxO 3 samples, the effective magnetic moments calculated are similar to NdNiO3, in agreement with previous works that reported on Co 3+ in low spin state at low temperatures [7]. It is important to note that no S = i Ni3+ contribution has been specifically detected in all samples and no magnetic anomalies have been found in the whole temperature range. The temperature dependence of the resistivity between 4.2 and 300 K is shown in Fig. 2. NdNiO 3 is characterized by an MI phase transition at 205 K with a large thermal hysteresis [5]. The main effect of Ni substitution is the temperature decrease or disappearance of the MI phase transition. NdNil_xMxO 3 (M = Fe, Co or Cu) samples with x = 0.05 show a decrease of the MI phase transition
from 205 down to 120 and 130 K for Fe and Co substitutions respectively, and the disappearance for Cu substitution. For x = 0.1 samples, the MI phase transition with thermal hysteresis has disappeared in all samples. Substitution by Cu gives metallic samples, and by Co or Fe yields samples with, practically, temperature-independent behaviour. In the case of Co sample, it shows a positive slope from 300 down to 50 K (metallic) and negative at lower temperatures. For Fe compound the slope is practically negative (semiconductor) in the whole temperature range. For higher Fe or Co content, the samples are semiconducting. In a general way, the effects of Ni substitution are in agreement with the Torrance classification [6], hence increasing the substitution by Fe or Co increases the insulator character of the samples, while Cu substitution increases the metallic behaviour. On the other hand, low percentages of substitution by the three different atoms induce the same effect on the MI phase transition. These results indicate that a simple mechanism of a band gap, i.e. increase of the electronic density due to the replacement of Ni by Cu or decrease in the number of states at the Fermi level due to the more localized Fe 3+ or Co 3+ states, may explain the general electrical behaviour but cannot explain the stabilization of metallic phase in all cases for low percentages of substitution and the suppression of the MI phase transition. This suppression is not well understood in the frame of the current theories and some other mechanisms will be responsible for this phase transition. Furthermore, the absence of magnetic anomaly at the MI transition suggests large magnetic correlations in the high temperature phase. An explanation to the behaviour at low percentages of substitution could be the change of the electronic states responsible for the conductivity properties due to the occupational disorder induced by substitution. It has been proposed that there is a characteristic spin density wave ordering at the NdNiO 3 phase transition [4]. The disorder induced by low percentages of substitution may break the phase coherence for the localization of the spin density wave resulting in an increase of the metallic range. Acknowledgement: This work has been supported by CICYT MAT93-0240-C04-04 and PB92-1077 projects. References
[1] [2] [3] [4] [5] [6] [7]
J.B. Goodenough, Prog. Solid State Chem. 5 (1972) 145. J.K. Vassiliou et al., J. Solid State Chem. 81 (1989) 208. J.B. Torrance et al., Phys. Rev. B 45 (14) (1992) 8209. J.L. Garcia-Mufioz et al., Europhys. Lett. 20 (3) (1992) 241. J. Blasco et al., J. Phys: Condens. Matter 6 (1994) 5875. J.B. Torrance et al., Physica C 182 (1991) 351. D.S. Rajoria et al., J.C.S. Faraday II 70 (1974) 512.