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Spin-glass behaviour in the NdNi1−xCoxO3 system
Journal of Magnetism and Magnetic Materials 140-144 (1995) 1813-1814
Journal of magnetism and magnetic materials
•i• ELSEVIER
Spin-glass behaviour in the NdNil_xCOxO3 system J. Blasco *, J. Garcla, F.J. Lfizaro, M.G. Proietti L C.M,4., CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain
Abstract NdNil_xCOxO 3 (0 _
In recent years there has been a great interest in the study of perovskite oxides due to the variety of their physical properties [1]. Among these compounds, NdNiO 3 shows a metal-nonmetal (MI) phase transition with a large thermal hysteresis [2] while NdCoO 3 is a semiconducting compound with the Co 3+ ion in presumably low spin state [3]. Samples with nominal composition NdNil_xCOxO 3 (x from 0 up to 1 in steps of 0.1) were prepared by a sol-gel method as has been reported elsewhere [4]. X-ray diffraction patterns were performed in a Rigaku D / m a x - B system using Cu K,~ radiation. The X-ray patterns show single phases for the whole series which can be indexed in an orthorhombic unit cell with parameters ranging between those of NdNiO 3 and those of NdCoO 3 as shown in Fig. 1. The unit cell volume diminishes with the Co content as expected from the Co and Ni ionic sizes, but the lattice parameters do not follow this trend. At intermediate concentrations (0.3 < x < 0.8), the a and b parameters are nearly equal or even b > a. We have performed X-ray profile analysis in some samples resulting the Pbnm space group for the whole system [5]. In addition, EDS analysis on TEM images have shown a great homogeneity of the atomic composition of the different crystallites. The compositions correspond with the expected one from the starting material. No additional phases were detected. The ac magnetic susceptibility from 4.2 K up to 300 K were measured in the whole series. While at high temperatures ( > 100 K) the samples show a Curie-Weiss-like behaviour [6], at low temperatures a magnetic anomaly is found around 28 K in samples with Co content between
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Fig. 1. Lattice parameters of NdNil_xCOxO3 system versus Co content (x) in the sample.
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Fig. 2. AC magnetic susceptibility versus temperature between 4.2 K and 60 K for NdNil_xCOxO3 system.
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD1 0304-8853(94)00834-5
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* Corresponding author. Fax: 34-76-553773; email: [email protected].
'
J. Blasco et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 1813-1814
1814 1.2 10 .3
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T (K) Fig. 3. Measurements of ac magnetic susceptibility for NdNi0.3Co0.703 sample between 4.2 and 60 K at different frequencies of the external magnetic field. Frequencies are given in the figure. x = 0.3 and x = 0.8, as can be seen in Fig. 2. The largest anomaly is observed for the NdNio.3Co0.70 3 sample at 27 K. The maxima are almost at the same temperature except for the case of x = 0.8 that shows a peak at 20 K. The anomaly also appears in the out of phase component, X". In order to study this anomaly, we have performed Xac experiments at different ac frequencies. As it is shown in Fig. 3, the peak shifts to lower temperatures as the frequency is decreased. This two results can be explained in terms of magnetic relaxation processes. In order to determine if thermal story dependence occur, magnetization measurements, cooling the x = 0.7 sample with an external magnetic field of 386 Oe (FC curve) and without magnetic field (ZFC), were carded out. The large difference between FC and ZFC M(T) magnetization clearly shows the presence of magnetic story dependence effects 0.5
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.~. . . . . . . . . . . . . . . . . . . . . . . . . •
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References
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FC
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ZFC
[1] [2] [3] [4] [5] [6]
~ °°
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in this system (see Fig. 4). A different remanence was also observed and M(0) depends on the thermal, ZFC or FC, story treatment. The behaviour observed is characteristic of a spin-glass phase transition, however it could be due to the presence of small ferromagnetic particles. This last possibility has been discarded because XRD and, specially, TEM experiments have not detected any kind of impurity. Two conditions must be fulfilled for spin-glass formation: randomness and frustration. Although we have randomness between the Ni and Co positions, it is speculative to assign where the magnetic moment is located and what types of interactions would produce frustration. On the one hand, Ni has been described as Ni 3÷ (S = 1) in NdNiO3, coupled antiferromagnetically with two of the four on-plane Ni neighbors, and ferromagnetically with the other two [2]. So that, the random partial replacement of Ni by Co could be the origin of frustration. On the other hand, several works have found magnetic anomalies in ReCoO 3 samples [7] although Co 3÷ has been described mainly as low spin (S = 0) at low temperatures [3]. By comparison with the related La2NiO 4 [8] or Lal_xSrxCuO 4 systems [9], we can argue a similar mechanism for our system in which antiferromagnetic M - M interactions compete with the ferromagnetic coupling via the hole localized in the oxygen atom. This mechanism is in agreement with absorption experiments at the Ni K edge indicating that the oxidation state of the Ni atom is Ni 2÷ and the hole is localized mainly in oxygen atoms (p5 character) [10]. We conclude that this spin-glass like behaviour is characteristic of this system but its origin is still unclear. Note that a relationship between spin-glass behaviour and orthorhombic distortion seems to exist as can be deduced from Fig. 1. Acknowledgements: This work has been supported by CICYT MAT93-0240-C04-04 and PB92-1077 projects.
~OOoSo~Oeo ~ ..................... 10 20
,..t 30
40
.... 50
60
T (K)
Fig. 4, Magnetization versus temperature for NdNio.3Coo.703 sample with a external magnetic field of 386 Oe cooling with (FC curve) or without (ZFC curve) magnetic field.
[7] [8] [9] [10]
Goodenough J.B., Prog. Sol. State Chem. 5 (1972) 145. Torrance J.B. et al., Phys. Rev. B 45 (14) (1992) 8209. Rajoria D.S. et al., J.C.S. Faraday II 70 (1974) 512. Blasco J. et al., J. Phys: Cond. Matt. 6 (1994) 5875. Blasco J. et al., J. Phys. Chem. Sol. 55 (1994) 843. Blasco J. et al., L Magn. Magn. Mater. 140-144 (1994) 2155 (these Proceedings). Menyuk N. et al., J. Phys. Chem. Sol. 28 (1967) 549. Strangfeld Th. et al., Physica C 183 (1991) 1. Aharony A. et al., Phys. Rev. Lett. 60 (1988) 1330. J. Garcla et al., Proceedings of XAFS8, Berlin (1994).
Journal of magnetism and magnetic materials
•i• ELSEVIER
Spin-glass behaviour in the NdNil_xCOxO3 system J. Blasco *, J. Garcla, F.J. Lfizaro, M.G. Proietti L C.M,4., CSIC-Universidad de Zaragoza, 50009 Zaragoza, Spain
Abstract NdNil_xCOxO 3 (0 _
In recent years there has been a great interest in the study of perovskite oxides due to the variety of their physical properties [1]. Among these compounds, NdNiO 3 shows a metal-nonmetal (MI) phase transition with a large thermal hysteresis [2] while NdCoO 3 is a semiconducting compound with the Co 3+ ion in presumably low spin state [3]. Samples with nominal composition NdNil_xCOxO 3 (x from 0 up to 1 in steps of 0.1) were prepared by a sol-gel method as has been reported elsewhere [4]. X-ray diffraction patterns were performed in a Rigaku D / m a x - B system using Cu K,~ radiation. The X-ray patterns show single phases for the whole series which can be indexed in an orthorhombic unit cell with parameters ranging between those of NdNiO 3 and those of NdCoO 3 as shown in Fig. 1. The unit cell volume diminishes with the Co content as expected from the Co and Ni ionic sizes, but the lattice parameters do not follow this trend. At intermediate concentrations (0.3 < x < 0.8), the a and b parameters are nearly equal or even b > a. We have performed X-ray profile analysis in some samples resulting the Pbnm space group for the whole system [5]. In addition, EDS analysis on TEM images have shown a great homogeneity of the atomic composition of the different crystallites. The compositions correspond with the expected one from the starting material. No additional phases were detected. The ac magnetic susceptibility from 4.2 K up to 300 K were measured in the whole series. While at high temperatures ( > 100 K) the samples show a Curie-Weiss-like behaviour [6], at low temperatures a magnetic anomaly is found around 28 K in samples with Co content between
5.42
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Fig. 1. Lattice parameters of NdNil_xCOxO3 system versus Co content (x) in the sample.
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x=0.9
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20
30 40 T (K)
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Fig. 2. AC magnetic susceptibility versus temperature between 4.2 K and 60 K for NdNil_xCOxO3 system.
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD1 0304-8853(94)00834-5
'
a
0100
* Corresponding author. Fax: 34-76-553773; email: [email protected].
'
J. Blasco et al. /Journal of Magnetism and Magnetic Materials 140-144 (1995) 1813-1814
1814 1.2 10 .3
....
, ....
, ....
1.0 10 .3
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s.o lo-'
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4.0 10 .4
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~:J~°°
2.0 10 .4
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........................... 10
20
30
40
50
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T (K) Fig. 3. Measurements of ac magnetic susceptibility for NdNi0.3Co0.703 sample between 4.2 and 60 K at different frequencies of the external magnetic field. Frequencies are given in the figure. x = 0.3 and x = 0.8, as can be seen in Fig. 2. The largest anomaly is observed for the NdNio.3Co0.70 3 sample at 27 K. The maxima are almost at the same temperature except for the case of x = 0.8 that shows a peak at 20 K. The anomaly also appears in the out of phase component, X". In order to study this anomaly, we have performed Xac experiments at different ac frequencies. As it is shown in Fig. 3, the peak shifts to lower temperatures as the frequency is decreased. This two results can be explained in terms of magnetic relaxation processes. In order to determine if thermal story dependence occur, magnetization measurements, cooling the x = 0.7 sample with an external magnetic field of 386 Oe (FC curve) and without magnetic field (ZFC), were carded out. The large difference between FC and ZFC M(T) magnetization clearly shows the presence of magnetic story dependence effects 0.5
0.4
.~. . . . . . . . . . . . . . . . . . . . . . . . . •
0.3
:~
References
•
FC
c
ZFC
[1] [2] [3] [4] [5] [6]
~ °°
0.2 % o o e 8 0.1 0
in this system (see Fig. 4). A different remanence was also observed and M(0) depends on the thermal, ZFC or FC, story treatment. The behaviour observed is characteristic of a spin-glass phase transition, however it could be due to the presence of small ferromagnetic particles. This last possibility has been discarded because XRD and, specially, TEM experiments have not detected any kind of impurity. Two conditions must be fulfilled for spin-glass formation: randomness and frustration. Although we have randomness between the Ni and Co positions, it is speculative to assign where the magnetic moment is located and what types of interactions would produce frustration. On the one hand, Ni has been described as Ni 3÷ (S = 1) in NdNiO3, coupled antiferromagnetically with two of the four on-plane Ni neighbors, and ferromagnetically with the other two [2]. So that, the random partial replacement of Ni by Co could be the origin of frustration. On the other hand, several works have found magnetic anomalies in ReCoO 3 samples [7] although Co 3÷ has been described mainly as low spin (S = 0) at low temperatures [3]. By comparison with the related La2NiO 4 [8] or Lal_xSrxCuO 4 systems [9], we can argue a similar mechanism for our system in which antiferromagnetic M - M interactions compete with the ferromagnetic coupling via the hole localized in the oxygen atom. This mechanism is in agreement with absorption experiments at the Ni K edge indicating that the oxidation state of the Ni atom is Ni 2÷ and the hole is localized mainly in oxygen atoms (p5 character) [10]. We conclude that this spin-glass like behaviour is characteristic of this system but its origin is still unclear. Note that a relationship between spin-glass behaviour and orthorhombic distortion seems to exist as can be deduced from Fig. 1. Acknowledgements: This work has been supported by CICYT MAT93-0240-C04-04 and PB92-1077 projects.
~OOoSo~Oeo ~ ..................... 10 20
,..t 30
40
.... 50
60
T (K)
Fig. 4, Magnetization versus temperature for NdNio.3Coo.703 sample with a external magnetic field of 386 Oe cooling with (FC curve) or without (ZFC curve) magnetic field.
[7] [8] [9] [10]
Goodenough J.B., Prog. Sol. State Chem. 5 (1972) 145. Torrance J.B. et al., Phys. Rev. B 45 (14) (1992) 8209. Rajoria D.S. et al., J.C.S. Faraday II 70 (1974) 512. Blasco J. et al., J. Phys: Cond. Matt. 6 (1994) 5875. Blasco J. et al., J. Phys. Chem. Sol. 55 (1994) 843. Blasco J. et al., L Magn. Magn. Mater. 140-144 (1994) 2155 (these Proceedings). Menyuk N. et al., J. Phys. Chem. Sol. 28 (1967) 549. Strangfeld Th. et al., Physica C 183 (1991) 1. Aharony A. et al., Phys. Rev. Lett. 60 (1988) 1330. J. Garcla et al., Proceedings of XAFS8, Berlin (1994).