TY - JOUR
T1 - Dielectric response to the low-temperature magnetic defect structure and spin state transition in polycrystalline LaCoO3
AU - Schmidt, Rainer
AU - Wu, J.
AU - Leighton, C.
AU - Terry, I.
PY - 2009/3/3
Y1 - 2009/3/3
N2 - The dielectric and magnetic properties and their correlations were investigated in polycrystalline perovskite LaCoO3-δ. 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 Co3+ low-spin (LS) (S=0; t 2g 6 eg0) to a higher spin state occurs at Ts1 80 K, which is controversial in nature and has been suggested to be an intermediate-spin (IS) state (S=1; t 2g 5 eg1) or a high-spin (HS) state (S=2; t 2g 4 eg2) 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< Ts1, 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.
AB - The dielectric and magnetic properties and their correlations were investigated in polycrystalline perovskite LaCoO3-δ. 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 Co3+ low-spin (LS) (S=0; t 2g 6 eg0) to a higher spin state occurs at Ts1 80 K, which is controversial in nature and has been suggested to be an intermediate-spin (IS) state (S=1; t 2g 5 eg1) or a high-spin (HS) state (S=2; t 2g 4 eg2) 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< Ts1, 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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U2 - 10.1103/PhysRevB.79.125105
DO - 10.1103/PhysRevB.79.125105
M3 - Article
AN - SCOPUS:63249089136
SN - 1098-0121
VL - 79
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 12
M1 - 125105
ER -