Metal-insulator transition, giant negative magnetoresistance, and ferromagnetism in LaCo1-yNiyO3

D. Hammer, J. Wu, C. Leighton

Research output: Contribution to journalArticle

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Abstract

We have investigated the transport and magnetic properties of the perovskite LaCo1-yNiyO3, an alloy of LaCoO 3 (a semiconductor that exhibits spin-state transitions) and LaNiO3 (a paramagnetic metal). The metal-insulator transition (MIT) was found to occur at y = 0.40. On the insulating side of the transition the conductivity obeys Mott variable range hopping with a characteristic temperature (T0) that varies with y in a manner consistent with the predictions of the scaling theory of electron localization. On the metallic side the low temperature conductivity (down to 0.35 K) varies as T 1/2 due to the effects of electron-electron interaction in the presence of disorder. The composition dependence of the low-temperature conductivity in the critical region fits the scaling theory of electron localization with a conductivity critical exponent close to unity, consistent with the scaling of T0 in the insulating phase. A large negative magnetoresistance is observed (up to 70% in 17 T) which increases monotonically with decreasing temperature and is smoothly decreased through the MIT. The magnetic properties show that doping LaCoO3 with Ni leads to a rapid destruction of the low spin-state for Co3+ ions, followed by the onset of distinct ferromagnetic interactions at higher Ni content. Similar to La1-xSrxCoO3, the system shows a smooth evolution from spin-glass to ferromagnetic ground states, which is interpreted in terms of the formation of ferromagnetic clusters. In contrast to La 1-xSrxCoO3 further doping does not lead to a bulk ferromagnetlike state with a large TC, despite the clear existence of ferromagnetic interactions. We suggest that this is due to a limitation of the strength of the ferromagnetic interactions, which could be related to the fact that Ni rich clusters are not thermodynamically stable. The ferromagnetic clusters in LaCo1-yNiyO3 do not percolate with increasing y explaining the lack of a high-TC ferromagnetic state and the fact that the MIT is a simple Mott-Anderson transition rather than a percolation transition. Finally, in contrast to previous works (which focused on a single composition) we find no clear correlation between freezing temperature and the onset of magnetoresistance.

Original languageEnglish (US)
Article number134407
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume69
Issue number13
DOIs
StatePublished - Apr 1 2004

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Metal insulator transition
Ferromagnetism
Magnetoresistance
ferromagnetism
insulators
metals
conductivity
Magnetic properties
Temperature
Doping (additives)
scaling
Electron-electron interactions
Spin glass
Electrons
Chemical analysis
magnetic properties
Freezing
Perovskite
Transport properties
Ground state

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Metal-insulator transition, giant negative magnetoresistance, and ferromagnetism in LaCo1-yNiyO3. / Hammer, D.; Wu, J.; Leighton, C.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 69, No. 13, 134407, 01.04.2004.

Research output: Contribution to journalArticle

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abstract = "We have investigated the transport and magnetic properties of the perovskite LaCo1-yNiyO3, an alloy of LaCoO 3 (a semiconductor that exhibits spin-state transitions) and LaNiO3 (a paramagnetic metal). The metal-insulator transition (MIT) was found to occur at y = 0.40. On the insulating side of the transition the conductivity obeys Mott variable range hopping with a characteristic temperature (T0) that varies with y in a manner consistent with the predictions of the scaling theory of electron localization. On the metallic side the low temperature conductivity (down to 0.35 K) varies as T 1/2 due to the effects of electron-electron interaction in the presence of disorder. The composition dependence of the low-temperature conductivity in the critical region fits the scaling theory of electron localization with a conductivity critical exponent close to unity, consistent with the scaling of T0 in the insulating phase. A large negative magnetoresistance is observed (up to 70{\%} in 17 T) which increases monotonically with decreasing temperature and is smoothly decreased through the MIT. The magnetic properties show that doping LaCoO3 with Ni leads to a rapid destruction of the low spin-state for Co3+ ions, followed by the onset of distinct ferromagnetic interactions at higher Ni content. Similar to La1-xSrxCoO3, the system shows a smooth evolution from spin-glass to ferromagnetic ground states, which is interpreted in terms of the formation of ferromagnetic clusters. In contrast to La 1-xSrxCoO3 further doping does not lead to a bulk ferromagnetlike state with a large TC, despite the clear existence of ferromagnetic interactions. We suggest that this is due to a limitation of the strength of the ferromagnetic interactions, which could be related to the fact that Ni rich clusters are not thermodynamically stable. The ferromagnetic clusters in LaCo1-yNiyO3 do not percolate with increasing y explaining the lack of a high-TC ferromagnetic state and the fact that the MIT is a simple Mott-Anderson transition rather than a percolation transition. Finally, in contrast to previous works (which focused on a single composition) we find no clear correlation between freezing temperature and the onset of magnetoresistance.",
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