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Type: Artigo de periódico
Title: Magnetic Properties And Triple Valence Fluctuations Of Iron In Prsr2fe3o9-δ
Author: Nowik I.
Felner I.
Awana V.P.S.
Abstract: The compound PrSr2Fe3O9-δ (δ~<0.1) has been studied by magnetization and 57Fe Mössbauer spectroscopy measurements. The magnetization studies show magnetic hysteresis phenomena at low temperatures and three distinct phase transitions; an antiferromagnetic transition at TN=190 K, a transition at Tv=170 K associated with change in iron valence and Tirr=270 K, the merging temperature of the zero field and field cooled magnetization curves. Mössbauer studies confirm the TN and Tv values. Well below and above TN, the spectra are composed of two well-defined sub-spectra (ratio 2 : 1), though all Fe ions reside in one crystallographic site. At 4.2 K the subspectra differ in their isomer shift (IS) by 0.4 mm/s and in the magnetic hyperfine field (469 and 269 kOe) whereas above TN the difference in the IS is only 0.24 mm/s. For 90 K<T<TN the spectra are complex and cannot be interpreted in terms of well defined (2 or even 3) sub-spectra. All spectra, in the entire temperature range can be well explained and reproduced by a triple valence fluctuation model, assuming that Fe appear in three valence states. (a) 2Fe3++Fe5+ at low temperatures, (b) Fe3+ and 2Fe4+ above TN and (c) at 90 K<T<TN triple valence fluctuations occur: Fe3+↔Fe4+↔Fe5+. An electron is transferred from Fe3+ to Fe5+ to form two nonmagnetic Fe4+ ions. This process dilutes the magnetic ions concentration to a point of collapse of the magnetic order. © 1999 Elsevier Science B.V.
Rights: fechado
Identifier DOI: 
Date Issue: 1999
Appears in Collections:Unicamp - Artigos e Outros Documentos

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