Phase transition and magnetodielectric response in Ni0.5Co0.5Fe2O4 – BaTiO3 composites at cryogenic temperature

To fabricate magnetoelectric devices, magnetically switchable dielectric properties in functional multiferroic composites are a significant challenge. In this study, an attempt is made to synthesize multiferroic composite (1- x) Ni _0.5Co _0.5Fe ₂O ₄(NCFO) – x BaTiO ₃(BTO) ( x = 0, 0.6, 0.8, 1) using a solid-state route with tunable magnetodielectric (MD) properties. The microstructure of the composite revealed a highly dense and closed-packed structure with a maximum relative density of 97 % for the x = 0.8. The X-ray photoelectron spectroscopy (XPS) analysis showed that oxygen vacancy is suppressed from 25.1 % to 19.6 %, with increased BTO concentration. The maximum saturation magnetization of 26 emu/g and 29 emu/g is observed for x = 0.6 at 303 K and 10 K, respectively. The magnetic irreversibility between zero field cooled-field cooled (ZFC-FC) curves exhibited the larger magneto anisotropy of the composite sample. The dielectric properties are significantly changed with the magnetic field, indicating the signature of a strong magnetoelectric effect. Interestingly, a broad transition at ∼ 150 K and ∼ 286 K is observed corresponding to the BTO, which is attributed to rhombohedral to orthorhombic and orthorhombic to tetragonal phase transitions, respectively. For the x = 0.8, the maximum dielectric constant of ∼ 811 with a minimum dielectric loss of 0.04 is observed at 1 MHz. For the same composition, the maximum MD of ∼ 0.7 % and ∼ 1.2 % is observed at 300 K and 200 K, respectively. In addition, the different contributions and prone causes (intrinsic and extrinsic origin) of MD are revealed using the Cole-Cole plot. The strong MD effect and low dielectric loss of these composites make them suitable for multifunctional device applications such as magnetic sensors, magnetoelectric random access memory (MERAM), etc.