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|Type:||Artigo de periódico|
|Title:||Anomalous Phonon Shifts In The Paramagnetic Phase Of Multiferroic R Mn2 O5 (r=bi, Eu, Dy): Possible Manifestations Of Unconventional Magnetic Correlations|
|Abstract:||A Raman spectroscopic study of the high-frequency optical phonons in single crystals of the multiferroic system R Mn2 O5 (R=Bi, Eu, Dy) was performed. All studied materials show anomalous phonon shifts, below a new characteristic temperature for these materials, T* ∼60-65 K. The sign and magnitude of such shifts appear to be correlated with the ionic radius of R, envolving from softenings for R=Bi to hardenings for R=Dy and showing an intermediary behavior for R=Eu. Additional phonon anomalies were identified below ∼ TN ∼40-43 K, reflecting the onset of long-range ferroelectric and/or magnetic order of the Mn sublattice. Complementary dc-magnetic susceptibility [χ (T)] measurements for Bi Mn2 O5 up to 800 K yield a Curie-Weiss temperature θCW =-253 (3) K, revealing a fairly large frustration ratio (θCW TN =6.3). Deviations of χ (T) from a Curie-Weiss paramagnetic behavior due to magnetic correlations were observed below temperatures of the order of θCW, with the inverse susceptibility showing inflection points at ∼160 K and ∼ T*. Supported by χ (T) data, the anomalous Raman phonon shifts below T* are interpreted in terms of the spin-phonon coupling, in a scenario of strong magnetic correlations. Overall, these results support significant magnetic frustration, introduce a new characteristic temperature (T*), and suggest a surprisingly rich behavior for the magnetic correlations in the paramagnetic phase of this system. © 2006 The American Physical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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