%0 Journal Article
%A Schmidt, Rainer
%A Wu, J.
%A Leighton, C.
%A Terry, I.
%T Dielectric response to the low-temperature magnetic defect structure and spin state transition in polycrystalline LaCoO_(3)
%D 2009
%@ 1098-0121
%U https://hdl.handle.net/20.500.14352/44712
%X 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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