Abstract - In this paper, two series of silicon-doped cobalt ferrite samples with compositions of Co_1+y Si_xFe_2−x-yO₄, were prepared by conventional ceramic method. The samples were characterized by X-ray diffraction, scanning electron microscopy and vibrating sample magnetometry. The magnetostriction coefficients were measured using tensile strain gauge technique. This study analyzed the influence of sintering temperature and of the chemical composition on magnetostriction coefficients. At low level of Si substitution for Fe cations cobalt ferrite can be good candidates for sensors application.

 

Two series of silicon-doped cobalt ferrite samples with compositions of Co_1+y Si_xFe_2−x-yO₄, were prepared by conventional ceramic method with the reason to determine the influence of the Si substitution level and of the sintering temperature on the magnetoelastic properties of cobalt ferrites. One of the series of CoSi_xFe_2−xO₄ ferrites, were y=0 and x ranges from 0.1 to 0.6 in steps of 0.1, was sintered at 1250°C for 4 hours in air followed by air cooling to the room temperature. The second series of ferrite with y=0.3 and x=0.3 Co_1,3Si_0,3Fe_1,4O₄ was obtained by varying the sintering temperature from 1250°C to 1325°C in steps of 25°C. The magnetic properties were carried out by VSM measurement and magnetostriction coefficients were measured using tensile strain gauge technique, at room temperature.

 

The specific magnetization of the Si doped cobalt ferrite samples decreased monotonically by increasing the amount of Si substitution for Fe. For ferrite with Co cations in excess the values of the specific magnetization depend on the sintering temperature and are lower than the values of the specific magnetization of Si doped cobalt ferrite samples. The values of the coercive field slowly increase by increasing the amount of Si substitution for Fe cations. For Co_1,3Si_0,3Fe_1,4O₄ samples the coercive field decreased monotonically by increasing the sintering temperature. The magnetostriction coefficient was measured along the applied magnetic field direction and has negative values. The value of the maximum magnetostriction coefficient is obtained for  x=0 and y=0 (-94 ppm). The sample with lowest Si contents CoSi_0.1Fe_1.9O₄ has maximum magnetostriction (-91 ppm) from the substituted series. Further increase in Si content reduced the maximum value of the magnetostriction coefficient. For the Co_1,3Si_0,3Fe_1,4O₄ samples the increase of the sintering temperature determined the increase of maximum magnetostriction coefficients. The sample sintered at 1325°C has the maximum magnetostriction coefficient (-100ppm). The values of the magnetostriction coefficients for Si cations substituted ferrites are smaller than the values observed fo the samples with Co cations in excess (see the Fig1).

 

 

 

 

Small amounts of Si promoted a small decrease of the magnetostriction coefficients and improved the field rate dependence of the magnetostriction. The Co cations in excess ensured a small increase of the coefficients and field rate dependence of the magnetostriction but the specific magnetization decrease.

At low level of Si substitution for Fe cations cobalt ferrite can be good candidates for sensors application while small Co excess deteriorate the magnetostrictive properties.

 

[1] J. A. Paulsen et al., Study of the Curie temperature of cobalt ferrite based composites for stress sensor applications IEEE, Trans. Magn.(2003) 39 (5) pp. 3316

 

Acknowledgements

These results were obtained in the MASTRICH project CEEX 73c/2006, financed by MATNANTECH Program of Romanian Ministry of Education and Research.