skip to main content

Title: Magnetothermopower, magnetic entropy change, and magnetoresistance in ferromagnetic cobaltites: R{sub 0.7}Sr{sub 0.3}CoO{sub 3} (R = La and Gd)

We compare the impact effect of external magnetic fields on the magnetic entropy (S{sub m}), electrical resistivity, and thermopower in two metallic oxides R{sub 0.7}Sr{sub 0.3}CoO{sub 3} that become ferromagnetic below T{sub C} = 240 K and 117 K for R = La{sup 3+}(4f{sup 0}) and Gd{sup 3+}(4f{sup 7}), respectively. While Gd{sub 0.7}Sr{sub 0.3}CoO{sub 3} shows unusually high values of negative magnetothermopower (≈−35.5%), magnetic entropy change (ΔS{sub m} ≈ −12 J/kg K), and negative magnetoresistance (≈−3.7%) at 10 K for a field change of 5 T, these effects are absent in the La sample at 10 K. We suggest that the large ΔS{sub m} arises from the field-induced suppression of spin fluctuations associated with localized 4f{sup 7} moments of Gd{sup 3+} ions, but magnetic interaction among Co ions dictates magnetoresistance and magnetothermopower. Magnetization data indicate that while Co{sup 3+} ions adopt intermediate spin state (S = 1) in the La compound, major fraction of them transforms into low spin state (S = 0) in the Gd sample. Hence, the Gd sample is microscopically heterogeneous with a mixture of ferromagnetic metallic and paramagnetic metallic clusters. Spin dependent scattering at the surface of ferromagnetic clusters may be the cause for the coexistence of magnetothermopower and magnetoresistance in this compound. A close correlation between the magnetoresistance andmore » the magnetothermopower is reported.« less
Authors:
;  [1]
  1. Department of Physics, Faculty of Science, National University of Singapore, 2 Science Drive 3, Singapore 117551 (Singapore)
Publication Date:
OSTI Identifier:
22398854
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 106; Journal Issue: 14; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COBALT IONS; COBALT OXIDES; COMPARATIVE EVALUATIONS; CORRELATIONS; ENTROPY; FLUCTUATIONS; GADOLINIUM COMPOUNDS; GADOLINIUM IONS; LANTHANUM COMPOUNDS; LANTHANUM IONS; MAGNETIC FIELDS; MAGNETIZATION; MAGNETORESISTANCE; PARAMAGNETISM; SPIN; STRONTIUM COMPOUNDS; SURFACES