Magnetic exchange and charge transfer in mixed-valence manganites and cuprates
- Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachussetts 02173 (United States)
Metallic resistivity occurs at cryogenic temperatures in insulators with small carrier trap energies, e.g., superconducting cuprates. A similar metallic regime has been reported for the lanthanide (RE) manganites (RE{sup 3+}{sub 1{minus}{ital x}}A{sup 2+}{sub {ital x}})MnO{sub 3}. To interpret the anomalous resistivity {rho} as a function of temperature and magnetic field in these compounds, a model constructed from the relation for mobility activated semiconduction and the Brillouin{endash}Weiss theory of ferromagnetism has been developed. The resistivity maximum occurs at the susceptibility peak slightly above the Curie temperature {ital T}{sub {ital C}} and its magnitude is related to the hopping electron trap energy {ital E}{sub hop} by exp({ital E}{sub hop}/{ital kT}{sub {ital C}}). Where {ital T}{lt}{ital T}{sub {ital C}}, {rho} is metallic because {ital E}{sub hop} is small due to the collinear polarization of spins. For {ital T}{ge}{ital T}{sub {ital C}}, {ital E}{sub hop} increases to a value {approximately}0.1 eV equal to the decrease in stabilization energy of the transfer electrons caused by the transition from spin alignment to disorder. The magnetoresistance sensitivity {ital d}{rho}/{ital dH} at {ital T}={ital T}{sub {ital C}} is controlled by {ital T}{sub {ital C}} through (1/{ital T}{sub {ital C}})exp({ital E}{sub hop}/{ital kT}{sub {ital C}}). The relative sensitivity (1/{rho}){ital d}{rho}/{ital dH}, however, is proportional to 1/{ital T}{sup 2}{sub {ital C}}. These results also reinforce the concept that metallic resistivity in the superconducting cuprates occurs because of the frustration of antiferromagnetism. {copyright} {ital 1996 American Institute of Physics.}
- OSTI ID:
- 280037
- Report Number(s):
- CONF-951101--
- Journal Information:
- Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 8 Vol. 79; ISSN JAPIAU; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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