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Physics and Chemistry of Minerals

, Volume 31, Issue 9, pp 625–632 | Cite as

Changes in the structural and magnetic properties of Ni–substituted hematite prepared from metal oxinates

  • C. SaragoviEmail author
  • J. Arpe
  • E. Sileo
  • R. Zysler
  • L. C. Sanchez
  • C. A. Barrero
Article

Abstract

Samples prepared by the novel method based on the thermal decomposition at 700 °C in air of mixed Fe and Ni oxinates were characterized by thermogravimetric analysis, X-ray diffraction, magnetization measurements, and variable-temperature Mössbauer spectroscopy. It is found that the combustion treatment produces Ni-hematite and trevorite, the fraction of the latter increasing with the increment of Ni in the metal oxinates. Results indicate that the substitution of Ni2+ for Fe3+ in the hematite structure, which was found to be less than 5.3 mol%, is accompanied by the presence of oxygen and structural vacancy sites. Both the metal replacement and the presence of defects cause the a and c cell hematite parameters to decrease. The Néel temperature and the difference between the saturation fields for the antiferromagnetic AF and the weakly ferromagnetic WF phases are also found to decrease with nickel content. These effects are due to the fact that the magnetic behavior of hematite depends on the presence of Ni, vacancy sites, and lattice distortion. The large decrease in the Néel temperature with Ni doping suggests that structural vacancies are also present On the contrary, Ni incorporation does not appreciably affect the Morin temperature and the temperature range in which both AF and WF phases coexist. It is suggested that these effects are probably due to the differing effects that Ni and defects can produce on the magnetic dipolar and the single ion anisotropies.

Keywords

Mössbauer spectroscopy Ni-doped hematite Magnetic properties Morín transition Néel temperature 

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Notes

Acknowledgments.

To Geraldo Magela da Costa for kindly providing the iron and nickel oxinates. Thanks also go to COLCIENCIAS (Colombia) and CONICET (Argentina) through the CIAM program for finantial support. C.A.B. acknowledges CODI (Universidad de Antioquia).

Copyright information

© Springer-Verlag Berlin Heidelberg 2004

Authors and Affiliations

  • C. Saragovi
    • 1
    Email author
  • J. Arpe
    • 1
  • E. Sileo
    • 2
  • R. Zysler
    • 3
  • L. C. Sanchez
    • 4
  • C. A. Barrero
    • 4
  1. 1.Departamento de FísicaComisión Nacional de Energía Atómica (CNEA)San MartínArgentina
  2. 2.INQUIMAE y Departamento de Química Inorgánica, Analítica y Química Física, Facultad de Ciencias Exactas y NaturalesUniversidad de Buenos Aires, Pabellón IICiudad UniversitariaArgentina
  3. 3.Centro Atómico Bariloche (CNEA)S.C. de BarilocheArgentina
  4. 4.Grupo de Estado SólidoInstituto de Física, Universidad de AntioquiaMedellínColombia

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