57Fe Mössbauer spectroscopic study of the spin-glass transitions in the mixed spinel series Mg0.9+xFe2(1-x)Ni0.1Ti0.1O4

Magnetically diluted materials with spinel structure can fulfil the conditions for spin-glass behaviour. On the other hand, such spinels were also reported to exhibit a superparamagnetic behaviour due to the existence of small magnetic clusters in the spinel lattice. In order to gain some insight in this controversial problem, a 57Fe Mössbauer spectroscopic study has been performed on some new spinel compounds with general formula Mg+x-yFe2(1-x)NiyTixO4 with x=0.5, 0.6 and 0.7 and y being 0.1. The Ni2+ was introduced with the aim to resolve better the contributions of both spinel sublattices in the external-field Mössbauer spectra. In the first place, special attention has been paid to the preparation procedures. It has been found that as-prepared samples show a predominant superparamagnetic behaviour due to magnetic clusters within the sample. After repeating the heating process for at least three times the samples behave more as a spin glass. From the Mössbauer experiments it has been shown that for the composition with x=0.7 a direct transition from paramagnetism to spin glass occurs on cooling, whereas for the compositions with x=0.5 and 0.6 an intermediate ferrimagnetic phase is observed with a transversal spin relaxation on the octahedral sites. At lower temperatures these compositions freeze to a spin glass on the octahedral sites while the spins on the tetrahedral sites remain mutually parallel and opposite to the net B-site moment. Finally, from the experimental data combined with the percollation thresholds reported in literature, boundary values with respect to composition and temperature could be derived enabling to draw up a complete magnetic phase diagram.

Grantor dc:publisher

Ghent University. Faculty of Sciences

Year dc:date

2009

Author dc:creator

• Alakrmi, Abdurazak

Contributors dc:contributor

• De Grave, Eddy
• Vandenberghe, Robert

• Physics and Astronomy

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://biblio.ugent.be/publication/811761
https://biblio.ugent.be/publication/811761/file/1886381

OAI identifier oai:identifier

oai:archive.ugent.be:811761