Improvement of magnetomechanical properties of cobalt ferrite by magnetic anneal

Improvements of both magnetostriction level and strain derivative of pure cobalt ferrite by magnetic annealing are reported. CoFe₂O₄ samples are annealed at 300°C in air for 36 hours in a vibrating sample magnetometer with a furnace. VSM measurements indicate a uniaxial anisotropy induced by magnetic anneal, with the easy axis being along the magnetic annealing field direction. Coercivities are measured to be 2.6 kA/m and 6.9 kA/m along the easy and hard axes, respectively. After magnetic annealing, the magnitude of the maximum magnetostriction is increased. This is attributed to the induced uniaxial anisotropy, by which domain magnetization tends to align along the easy axis in the absence of any applied field. When a magnetic field is applied along the hard axis, re-orientation of domain magnetization from the induced easy directions towards the field direction involves more rotation and non-180° domain wall processes.