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Dielectric response to the low-temperature magnetic defect structure and spin state transition in polycrystalline LaCoO_(3)

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Schmidt, Rainer and Wu, J. and Leighton, C. and Terry, I. (2009) Dielectric response to the low-temperature magnetic defect structure and spin state transition in polycrystalline LaCoO_(3). Physical review B, 79 (12). ISSN 1098-0121

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Official URL: http://dx.doi.org/10.1103/PhysRevB.79.125105


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http://journals.aps.org/Publisher


Abstract

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.


Item Type:Article
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© 2009 The American Physical Society. The authors wish to thank Neil Hyatt, Derek Sinclair, and Sean Giblin for useful discussions.

Uncontrolled Keywords:Metal transition.
Subjects:Sciences > Physics > Electricity
Sciences > Physics > Electronics
ID Code:32655
Deposited On:30 Jul 2015 09:42
Last Modified:10 Dec 2018 14:58

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