ISSN:
1434-6036
Keywords:
PACS. 61.12.-q Neutron diffraction and scattering – 71.30.+h Metal-insulator transitions and other electronic transitions – 75.50.Ee Antiferromagnetics
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract: The oxygen deficient cobaltites LnBaCo2O5 (Ln = Tb, Dy, Ho) exhibit two successive crystallographic transitions at T N ∼340 K and at T CO ∼210 K. Whereas the first transition (P4/mmm to Pmmm) is related to the long-range antiferromagnetic ordering of the Co ions (spin ordering), the second transition (Pmmm to Pmmb) corresponds to the long-range ordering of the Co2+ and Co3+ species (charge ordering) occurring in 1:1 ratio in the structure. The charge ordered (CO) state was directly evidenced by the observation of additional superstructure peaks using neutron and electron diffraction techniques. The CO state was also confirmed indirectly from refinement of high resolution neutron diffraction data as well as from resistivity and DSC measurements. From the refined saturated magnetic moment values only, ∼3.7 and ∼2.7 , the electronic configuration of the Co ions in LnBaCo2O5 remains conjectural. Two pictures, with Co3+ ions either in intermediate spin state ( t 5 2g e 1 g ) or in high spin state ( t 4 2g e 2 g ), describe equally well our experimental data. In both cases, the observed magnetic structure can be explained using the qualitative Goodenough-Kanamori rules for superexchange. Finally, in contrast to the parent Ln = Y compound [Vogt et al. , Phys. Rev. Lett. 84, 2969 (2000)], we do not report any spin transition in LnBaCo2O5 (Ln = Tb, Dy, Ho).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/PL00011119
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