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

Journal Article · Mon Apr 06 00:00:00 EDT 2015 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4917292· OSTI ID:22398854

Kumar, Pawan

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 and the magnetothermopower is reported.

• OSTI ID: 22398854
• Journal Information: Applied Physics Letters, Vol. 106, Issue 14; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

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