Variable-temperature Mössbauer spectroscopic study of nano-sized maghemite and Al-substituted maghemites.

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MetadadosDescriçãoIdioma
Autor(es): dc.creatorCosta, Geraldo Magela da-
Autor(es): dc.creatorGrave, Eddy De-
Autor(es): dc.creatorBowen, L. H.-
Autor(es): dc.creatorBakker, P. M. A. de-
Autor(es): dc.creatorVandenberghe, Robert Emile-
Data de aceite: dc.date.accessioned2025-08-21T15:08:51Z-
Data de disponibilização: dc.date.available2025-08-21T15:08:51Z-
Data de envio: dc.date.issued2017-05-30-
Data de envio: dc.date.issued2017-05-30-
Data de envio: dc.date.issued1995-
Fonte completa do material: dc.identifierhttp://www.repositorio.ufop.br/handle/123456789/7825-
Fonte completa do material: dc.identifierhttps://link.springer.com/article/10.1346/CCMN.1995.0430506-
Fonte completa do material: dc.identifierhttps://doi.org/10.1346/CCMN.1995.0430506-
Fonte: dc.identifier.urihttp://educapes.capes.gov.br/handle/capes/1003484-
Descrição: dc.descriptionSynthetic aluminum-substituted maghemite samples, "g-(Fe~ _xAlx)203, have been prepared by thermal decomposition of Al-lepidocrocite (3,-Fe~_xAlxOOH), with x = 0, 0.04, 0.06, 0.14 and 0.18. The particles are needle-shaped and the mean crystallite diameter along the [311] crystallographic direction was found to be between 2.0 and 5.0 nm. MSssbauer spectra were collected at 6 K and from 80 K up to 475 K at steps of 25 K. In a wide range of temperatures the spectra of the non-substituted sample consist of a superposition of a broad sextet and a superparamagnetic doublet, whereas for the Al-maghemites this range is much smaller. From the temperature variation of the fractional doublet area two different parameters were defined: the temperature corresponding to a 50/50 doublet-sextet spectrum (T1/2), and the temperature below which the doublet ceases to exist (To). These two parameters (T1/2 and To) decrease from 390 K and 92 K (Al-free sample), to 118 K and 64 K (4 mole % AI) and to 100 K and 48 K (18 mole % A1), respectively. The average hyperfine fields at 6 K undergo a steep drop in going from the AIfree sample (I:I~f = 506 kOe) to the sample with 4 mole % A1 (I:Ihr = 498 kOe), but for higher substitutions the effect is much smaller. The A- and B-site quadrupole splittings, obtained from the data between 220 K and 475 K, were found as: AEQ.A = 0.86 --+ 0.04 mm/s and AEo.B = 0.65 _+ 0.04 mm/s for the 4 mole % A1 sample. The characteristic MiJssbauer temperature, determined from the temperature dependence of the average isomer shift, was found to be in the range of 500-600 K.-
Formato: dc.formatapplication/pdf-
Idioma: dc.languageen-
Direitos: dc.rightsrestrito-
Palavras-chave: dc.subjectAl substitution-
Palavras-chave: dc.subjectMaghemite-
Palavras-chave: dc.subjectMossbauer effect-
Título: dc.titleVariable-temperature Mössbauer spectroscopic study of nano-sized maghemite and Al-substituted maghemites.-
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