The crystallographic structure and the magnetic order of the distorted perovskite La1-xSrxCoO3 (0.10≤x ≤0.30) has been studied by neutron diffraction, high-resolution electron microscopy, and magnetic-susceptibility measurements. The results give direct evidence for an inhomogeneous distribution of the Sr2+ ions and the segregation of the material into hole-rich ferromagnetic regions and a hole-poor semiconducting matrix at lower values of x. The holes introduced by Sr doping are attracted to the Sr2+ ions where they stabilize to lowest temperatures an intermediate-spin state at neighboring trivalent cobalt. The antibonding e electrons so stabilized increase the mean unit-cell volume and are delocalized over the cobalt atoms of the cluster where they couple the localized t5 configurations ferromagnetically. Long-range ferromagnetic order between clusters is realized even for Sr doping as low as x=0.10. The transition to a spin glass state is observed only for Sr concentrations smaller than 0.10. The volume of a hole-rich cluster grows in a magnetic field, and the origin of the large negative magnetoresistance observed near Tc for 0.15 ≤ x ≤ 0.25 appears to be due to a growth of the clusters to a percolation threshold. For x=0.30, the σ* band of the intermediate-spin state below Tc is at the threshold of a transition from itinerant to polaronic conduction and, above Tc, the system transforms smoothly to a cluster state.
Structural details and magnetic order of La1-xSrxCoO3 (x ≤ 0.3) / R., Caciuffo; Rinaldi, Daniele; Barucca, Gianni; J., Mira; J., Rivas; M. A., SEÑARÌS RODRÌGUEZ; P. G., Radaelli; D., Fiorani; J. B., Goodenough. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - 59(2):(1999), pp. 1068-1078. [10.1103/PhysRevB.59.1068]
Structural details and magnetic order of La1-xSrxCoO3 (x ≤ 0.3).
RINALDI, DANIELE;BARUCCA, Gianni;
1999-01-01
Abstract
The crystallographic structure and the magnetic order of the distorted perovskite La1-xSrxCoO3 (0.10≤x ≤0.30) has been studied by neutron diffraction, high-resolution electron microscopy, and magnetic-susceptibility measurements. The results give direct evidence for an inhomogeneous distribution of the Sr2+ ions and the segregation of the material into hole-rich ferromagnetic regions and a hole-poor semiconducting matrix at lower values of x. The holes introduced by Sr doping are attracted to the Sr2+ ions where they stabilize to lowest temperatures an intermediate-spin state at neighboring trivalent cobalt. The antibonding e electrons so stabilized increase the mean unit-cell volume and are delocalized over the cobalt atoms of the cluster where they couple the localized t5 configurations ferromagnetically. Long-range ferromagnetic order between clusters is realized even for Sr doping as low as x=0.10. The transition to a spin glass state is observed only for Sr concentrations smaller than 0.10. The volume of a hole-rich cluster grows in a magnetic field, and the origin of the large negative magnetoresistance observed near Tc for 0.15 ≤ x ≤ 0.25 appears to be due to a growth of the clusters to a percolation threshold. For x=0.30, the σ* band of the intermediate-spin state below Tc is at the threshold of a transition from itinerant to polaronic conduction and, above Tc, the system transforms smoothly to a cluster state.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.