The spinel CoFe₂O₄ shows saturation magnetostriction of about 200 ppm and is usually classified as a semi-hard magnetic material.
J. C. Slonczewski's 1958 Physical Review paper addressed the origin of magnetic anisotropy in cobalt-substituted magnetite, the solid-solution system behind CoFe₂O₄ tuning.
As a rare-earth-free magnetostrictive material it substitutes for Terfenol-D in sensors and actuators, and its nanoparticles serve as electrocatalysts and supercapacitor electrodes (reviewed in 2022 by Ortiz-Quiñonez, Das and Pal).