Compositional Dependence of the Magnetomechanical Effect in Substituted Cobalt Ferrite for Magnetoelastic Stress Sensors

This paper reports on a systematic system of the effects of Mn and Cr substitution on the magnetomechanical properties of cobalt ferrites, which hold promise for non-contact stress sensing applications due to their strong magnetomechanical coupling. Magnetomechanical tests were performed on sintered bulk CoMn_x Fe_2-x O₄ and CoCry Fe_2-y O₄ by measuring the change in surface field versus the sample strain under tension. The stress sensitivity first increases as a result of Mn or Cr substitution, peaks at x=0.2 and y=0.4, and decreases below that of pure cobalt ferrite at high Mn or Cr content. The strain derivative exhibits similar dependence on the Mn and Cr content. The results can be interpreted by considering stress-induced changes in magnetization against anisotropy, in which case the strain derivative and stress sensitivity are proportional to the ratio of saturation magnetostriction lambda _S to anisotropy K. Mn or Cr substitution reduces both lambda_S and K. However, for substitute contents in the vicinity of x=0.2 and y=0.4, K decreases more rapidly than lambda_S, causing lambda_S/K and hence the strain derivative and stress sensitivity to increase