Magnetic and Magnetomechanical Properties of CoAl $_{\rm x}$ Fe $_{2 - {\rm x}}$ O

The potential of CoAl_xFe_2-xO₄ (x = 0.1 to 0.9) for magnetomechanical stress sensor applications has been studied. It was found that the plot of magnetostriction against applied magnetic field changed shape as Al content increased. Furthermore, substituting with Al³⁺ resulted in the increase of the sensitivity of strain to applied magnetic field (dlambda/dH)_max. The maximum magnetostriction for the Al-doped (x = 0.1) was 34% lower than un-doped Co-ferrite but the (dlambda/dH)_max was 112% higher. The magnitude of magnetostriction obtained for Al-doped samples is still sufficient for stress sensor and actuator applications. Results were compared with those obtained for Ge-, Ga-, Cr- and Mn-doped Co-ferrites. It was found that in terms of improving strain response to applied field whilst maintaining significant amplitude of magnetostriction CoAl_xFe_2-xO₄ has promising potential for magnetomechanical stress sensor applications.