Dielectric and Magnetic Properties of Co-doped Ni_0.65Zn_0.35Fe₂O₄Thin Films Prepared by Using a Sol-gel Method

$Ni_0.65Zn_0.35Fe_2O_4$thin films were prepared by using a sol-gel method. Their crystallographic, dielectric and magnetic properties were investigated as a function of Cu contents by means of an X-ray diffractometer (XRD), X-ray reflectivity, LCZ meter (NF2232), a vibrating sample magnetometer (VSM), and an atomic force microscope (AFM). From typical C-V measurements for $Ni_0.65Zn_0.35Fe_2O_4$ thin films on p-type silicon substrate, the surface charge density was calculated as 1.4 ${\mu}$C/$m^2$. The dielectric constant evaluated from the capacitance at the accumulation state was 28. The high $H_c$ and low $M_sat$ at x=0.0 and 0.1 were due to the growth of the ${\alpha}$-$Fe_2O_3$ phase having antiferromagnetic properties. The rapidly decreased $H_c$ and increased $M_sat$ at x=0.2 and 0.3 can be explained that the ${\alpha}$-$Fe_2O_3$ phases have completely disappeared at x=0.3 and so, non-magnetic defects are minimized. The $M_sat$ was slightly decreased and the $H_c$ was increased above at x=0.3 because the increase of grain boundary due to smaller grain size acts as defects during magnetization process.