Magnetostrictive Properties of Cubic Cu0.6Co0.4Fe2O4 and Tetragonal Cu0.8Co0.2Fe2O4 Under Pulsed High Magnetic Fields

Abstract

To clarify the magnetostrictive properties of the Cu-substituted cobalt ferrites $\left(\mathrm{Cu}_{x} \mathrm{Co}_{1-x} \mathrm{Fe}_{2} \mathrm{O}_{4}\right)$ with spinel-type cubic and tetragonal structures, the magnetic field dependence of the strain was measured up to the saturation state using pulsed high magnetic fields. At 300 K, the strain-magnetic field curve of the $x=0.6$ sample with a cubic structure exhibited an extremum at approximately 1 T and then approached saturation. From the saturated values, the saturation magnetostriction constant $\lambda_{\mathrm{s}}$ was estimated to be -249 ppm. At the same temperature, the strain of the $x=0.8$ sample with a tetragonal structure varied gradually with increasing magnetic fields and approached saturation without showing an extremum. It was revealed that the $\lambda_{\mathrm{s}}$ value of the tetragonal $x=0.8$ sample was -309 ppm, which is larger than that of the cubic $x=0.6$ sample. Furthermore, for the cubic $x=0.6$ sample, the $\left|\lambda_{\mathrm{s}}\right|$ value increased with decreasing temperature and showed a maximum at approximately 100 K. In contrast, the $\left|\lambda_{\mathrm{s}}\right|$ value of the tetragonal $x=0.8$ sample monotonically decreased. These results suggest that the temperature dependence of the magnetostrictive properties of $\mathrm{Cu}_{x} \mathrm{Co}_{1-x} \mathrm{Fe}_{2} \mathrm{O}_{4}$ is strongly related to the crystal structure.