Fine–grained spinel ferrites: From the reactivity to magnetic properties

Laboratoire de Recherche sur la Réactivité des Solides (UMR 5613), Université de Bourgogne, 9 avenue Alain Savary, BP 400, 21011 Dijon Cedex, France

Corresponding author: bgillot@satie.u-bourgogne.fr

Received: 14 April 1998
Revised: 3 September 1998
Accepted: 3 September 1998
Published online: 15 December 1998

Abstract

The oxidation at low temperature of fine-grained ferrites containing oxidizable cations such as Cu⁺, Fe²⁺, Mn²⁺, Mo³⁺, V³⁺, has led to new mixed-valent cation deficient ferrites with a large number of vacancies. It has been demonstrated by DTG analysis that each cation oxidizes at a specific temperature in close relation with the cation-oxygen distance. The kinetics oxidation of each oxidizable cation has been explained on the basis of a diffusion-induced stress effect when these stresses are generated by the chemical gradient induced during the oxidation process. When fine-grained ferrites contain some Co-cations, it has been revealed that the stresses have a significant influence on the enhancement of the coercivity.