Magnetic Properties of TiFe2O4-Fe3O4 System and Their Change with Oxidation

Abstract

A series of solid solution xTiFe2O4.•E(1-x)Fe3O4 was synthesized by ceramic method over a whole range of the composition, 1• †_x• †_0. Changes of the Curie point, saturation moment and the lattice parameter with the composition were examined. Generalized titanomagnetite having some vacant site in the structure normally occupied in a spinel was also prepared by oxidizing the TiFe2O4-Fe3O4 solid solution series. The region within which the spinel structure can be in existence as a single phase was settled in a FeO-Fe2O3-TiO2 system. An equal lattice parameter line, equal Curie point line and equal saturation moment line for the generalized titanomagnetite were drawn on the FeO-Fe2O3-TiO2 system.

Estimation of the Curie Temperatures of Maghemite and Oxidized Titanomagnetites

“…If the BB interaction is relatively weak or positive due to direct exchange (Wickham and Goodenough, 1959) the B sublattice moment will remain relatively large as the Curie temperature approaches and the Neel P-type thermomagnetic curves will result (Neel, 1948). Titanium rich members of the titanomagnetite solid solution series show P-type behaviour as was first described by Akimoto et al (1957). Oxidized materials can show an even stronger P-type behaviour than the unoxidized materials (Sakamoto et al, 1968).…”

“…The Curie temperatures of oxidized titanomagnetites were first reported to be higher than the stoichiometric materials by Akimoto, Katsura and Yoshida (1957). Although the results of these workers are to some extent disputed (0'Reilly and this part of their work is confirmed by the increase in magnetization of wet ground titanomagnetites when held in air at 200-300C (Sakamoto, Ince and O'Reilly, 1968).…”

Unstable Components and Paleomagnetic Evidence for a Geomagnetic Polarity Transition

“…Curie points, such as those occurring in the upper parts of the magnetically unstable zone, are indicative of lower oxidation states (Akimoto et al, (1957).…”

Un calcul du paramètre cristallin des titanomagnétites oxydées

“…3), ont deja ete realisees. Les courbes obtenues par Akimoto et al (1957), qui ne couvrent qu'une partie de ce domaine, sont deduites d'experiences d'oxydation de titanomagnetites synthetiques. Elles ne sont probablement pas utilisables (Sanver et O'Reilly, 1970), car le procede experimental employe conduisait, en fait, non a une phase spinelle lacunaire unique, mais a plusieurs phases distinctes (O'Reilly et Ozima et Larson, 1970).…”

“…Si l'on compare les valeurs experimentales des parametres cristallins de titanomagnetites synthetisees par divers auteurs (Akimoto et al, 1957;Lindsley, 1962;Ghorbanian et Poix, 1965;Banerjee et al, 1967) aux courbes theoriques, calculees selon notre methode, correspondant aux trois modeles decrits, it apparait clairement que c'est le modele d'-Akimoto qui permet le mieux de rendre compte des resultats experimentaux (Fig. 2): pour x>0,5, parametres theoriques et experimentaux coincident et si, pour les valeurs plus faibles de x, la concordance est moms satisfaisante, l'ecart est neanmoins tres faible (0,005A au plus).…”