Dielectric response to the low-temperature magnetic defect structure and spin state transition in polycrystalline LaCoO_(3)
The dielectric and magnetic properties and their correlations were investigated in polycrystalline perovskite LaCoO_(3). The intrinsic bulk and grain-boundary (GB) dielectric relaxation processes were deconvoluted using impedance spectroscopy between 20 and 120 K, and resistivity and capacitance wer...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2009 |
| País: | España |
| Institución: | Universidad Complutense de Madrid (UCM) |
| Repositorio: | Docta Complutense |
| Idioma: | español |
| OAI Identifier: | oai:docta.ucm.es:20.500.14352/44712 |
| Acceso en línea: | https://hdl.handle.net/20.500.14352/44712 |
| Access Level: | acceso abierto |
| Palabra clave: | 537 Metal transition. Electricidad Electrónica (Física) 2202.03 Electricidad |
| Sumario: | The dielectric and magnetic properties and their correlations were investigated in polycrystalline perovskite LaCoO_(3). The intrinsic bulk and grain-boundary (GB) dielectric relaxation processes were deconvoluted using impedance spectroscopy between 20 and 120 K, and resistivity and capacitance were analyzed separately. A thermally induced magnetic transition from a Co^(3+) low-spin (LS) (S=0;t^(6)_(2g)e^(0)_(g)) to a higher spin state occurs at T_(s1) ≈ 80 K, which is controversial in nature and has been suggested to be an intermediate-spin (IS) state (S=1;t^(5)_(2g)e^(1)_(g)) or a high-spin(HS) state (S=2;t^(4)_(2g)e^(2)_(g)) transition. This spin state transition was confirmed by magnetic-susceptibility measurements and was reflected in the impedance by a split of the single GB relaxation process into two coexisting contributions. This apparent electronic phase coexistence at T > 80 K was interpreted as a reflection of the coexistence of magnetic LS and IS/HS states. At lower temperatures (T ≤ 40 K) perceptible variation in bulk dielectric permittivity with temperature appeared to be correlated with the magnetic susceptibility associated with a magnetic defect structure. At 40 K < T < T_(s1), separated GB and bulk resistivity vs T curves were consistent with localized polaron Mott variable-range hopping (VRH) based on impurity conduction. Below 40 K, a crossover from impurity Mott’s VRH to another type of thermally activated charge transport was detected, which was correlated with the appearance of the defect-related magnetism. |
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