Signature of multiferroicity and impedance analysis of Co_1−xZn_xFe_2−xLa_xO₄ nanoparticles

Effects of Zn²⁺/La³⁺ co-doping on multiferroic and impedance properties of co-precipitation derived Co_1−xZn_xFe_2−xLa_xO₄ (x = 0.0, 0.1 and 0.3) nanoparticles have been investigated. The powder X-ray diffraction study confirms the pure phase, cubic spinal structure and particle size varies between 20 and 22 nm. The particle size decreases with increase in co-substitution indicating the short range ordering in CoFe₂O₄. The relaxations in dielectric constant follow Maxwell–Wagner polarization and arise out of charge transfer of Co and Fe ions in multi-oxidation states. The co-substitution of Zn²⁺/La³⁺ in CoFe₂O₄ at A and B sites respectively results in improvement of Nquist plot and impedance of the nanoparticle which confirms space charge polarization caused by piling of charges at the interface of grain and grain boundries. An unusual relaxation behavior is also observed in co-substituted CoFe₂O₄ which may be useful in enhancing the multiferroic properties at room temperature. It could be noted the GBs are more resistive as compared to the grains, resulting in high impedance value and non-Debye type behavior in the Co_1−xZn_xFe_2−xLa_xO₄ nano particles. Low and stable coercivity (H_c) of 393.13 Oe have been observed and a stable saturation magnetization has been achieved at room temperature. P–E loops have rounded corners which may be the due to the aggregation of CoFe₂O₄ nanoparticles with each other resulting out of their strong magnetization. Simultaneous occurrence of saturation magnetization and weak ferroelectricity (P–E loop) with high values of impedance and dielectric constant confirm the signature of multiferroicity in Co_1−xZn_xFe_2−xLa_xO₄ nanoparticles.