Magnetic and electric properties of composites

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					The influence of dopants on the Curie temperature of Co ferrite Georgiana Dascalu, Luminita Boutiuc Hrib, Vasilica Gafton, O.F. Caltun Faculty of Physics and CARPATH Center, “Al. I. Cuza” University, 700506 Iasi, Romania
In the last years, the magnetostrictive materials for smart sensors have attracted a great interest because of their wide range of applications in the industry. Cobalt ferrites are promising materials for stress and torque sensor applications for which large value of strain derivative and high magnnetostrictive coefficient are desired properties, as well as low values of Curie temperature although it leads to negligible magnetomechanical hysteresis at room temperature. There are many studies concerning cobalt ferrites obtained by conventional ceramic technique. Recently, Mn and Si substitutions in Co ferrites have been reported to control the magnetomechanical hysteresis by decreasing the Curie temperature. 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 a series of cobalt ferrites with chemical compositions: CoFe2-xMnxO4 and CoSixFe2-xO4. These samples were synthesized by using standard powder ceramic technique. The microstructure of the samples was investigated using XRD and SEM analysis. Vibrating sample magnetometry and strain gauge measurements were used to characterize the magnetic and magnetostriction properties . The study results showed that a small amount of Mn substitution for iron decreases drastically the Curie temperature but also decreased the magnetostrictive coefficients. The same properties can be observed for Si substituted cobalt ferrites. The Curie temperature decreased from 530oC to 390oC with an increase of the Si concentration up to 0.6. An increase of the strain derivative was determined by an augmentation of the silicon concentration in the cobalt ferrite composites. The results demonstrate the possibility of controlling the magnetic and magnetomechanical properties through Mn and Si substitutions in this type of composites.