Superior magnetic, dielectric, and magnetodielectric effects in graphene/ZnCo₂O₄ nanocomposites

Although intensive research on spinel nanostructures has already been carried out, ZnCo₂O₄ is comparatively a less studied material because of its poor magnetic and dielectric properties. To focus ZnCo₂O₄ as a promising material with superior magnetic and dielectric properties in the present work, 2-dimentional nanosheets of ZnCo₂O₄ were synthesized using the large graphene surface as a template. Strong ferromagnetic behavior with asymmetries in coercivities is observed at room temperature. This was ascribed to the presence of Co ²⁺ and Co³⁺ ions in ZnCo₂O₄ which gave rise to uncompensated spins due to a superexchange interaction. The nanocomposites containing large interfaces between graphene and ZnCo ₂O₄ nanosheets exhibited unusual dielectric response due to trap states and superior magnetodielectric effect with an 18% change in dielectric permittivity for an applied magnetic field of 2.0 T as a result of combined effect between the Maxwell-Wagner polarization at the interface and a negative magnetoresistance of the ZnCo₂O₄ phase.