Substituted cobalt ferrites for sensors applications

The aim of this work was to study the influence of the sintering temperature and of the substitution level on the Curie temperature and on the magnetostriction coefficients for four series of cobalt ferrites sintered by conventional ceramic method. The microstructure of the samples was characterized using X-ray diffractometry and scanning surface electron microscopy. Vibrating sample magnetometry and strain gauge measurements were used to characterize the magnetic and magnetostriction properties. The study proves that a small amount of manganese substitution for iron decrease drastically the Curie temperature but in the same time decrease the specific magnetization and magnetostriction coefficient. Despite this drawback, the manganese substituted cobalt ferrites present the largest strain derivative. The maximum of the magnetostriction coefficient is also influenced by the stoichiometry of the cobalt ferrites. The magnetostriction coefficient of cobalt ferrite can be enhanced by substitution of small fraction of iron or cobalt by silicon or manganese, this implying the modification of the strain derivative as well as magnetostriction at lower magnetic fields. The maximum magnetostriction can be tuned by substitution levels and sintering parameters. (C) 2008 Elsevier B.V. All rights reserved.