Temperature Dependence of Magnetostriction of ${\rm Co}_{1+x}{\rm Ge}_{x}{\rm Fe}_{2-2x}{\rm O}_{4}$ for Magnetostrictive Sensor and Actuator Applications

The temperature dependence of the magnetoelastic properties of a series of germanium/cobalt co-substituted cobalt ferrite samples has been measured. Magnetostriction loops of the compositions Co_1+xGe_xFe_2-2xO₄ (x = 0.1 , 0.3, and 0.6) were measured over a temperature range of 250-400 K. Germanium/cobalt co-substitution was found to change the Curie temperature, anisotropy, and the magnetostriction coefficients in the crystal directions of [100] and [111]. Both magnetostriction and strain sensitivity were seen to decrease in magnitude with increasing temperature. Co_1.1Ge_0.1Fe_1.8O₄ was found to have a maximum sensitivity (dlambda/dH)_sigma of 2.6 times 10^-9 A^-1.m, which is twice the value obtained for pure cobalt ferrite, without any decrease in maximum magnetostriction in the linear region.