Spin glass freezing, magnetocapacitance and dielectric anomalies in 0.3NiFe₂O₄-0.7BiFeO₃ nanocomposite

We report on magnetocapacitance, spin dynamics through AC succeptability measurements and dielectric anomalies in 0.3NiFe₂O₄ – 0.7BiFeO₃ nanocomposite. Structural studies (purity and phase) and surface morphology of the 0.3NiFe₂O₄ – 0.7BiFeO₃ nanocomposite were examined by X-ray diffraction (XRD), Raman Spectra, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). TEM and SEM images indicate the uniform distribution of nanoparticles in parent pahase as well as in the composite. Energy dispersive X-ray (EDX) analysis indicates the presence of Ni, Fe, O and Bi elements in 0.3NiFe₂O₄ – 0.7BiFeO₃ nanocomposite. Magnetization measurements were performed at 300 K, 50 K and at 2 K and the Field Cooled (FC) and Zero Field Cooled (ZFC) measurements were carried out from 350 K to 2 K. ZFC and FC magnetization curves exhibit a hump around 30 K indicating the existence of competing magnetic interactions and possible spin galss behaviour. AC succeptibility measurements at various frequencies confirm the spin glass freezing behaviour of 0.3NiFe₂O₄ – 0.7BiFeO₃ nanocomposite around 25 K with the relaxation time and activation energy in the order of 10⁻⁷ s and 0.938 meV respectively. The dielectric constant and dielectric loss at various frequencies and temperatures indicate the dielectric relaxation behaviour of 0.3NiFe₂O₄ – 0.7BiFeO₃ nanocomposite. A rapid increase in the dielectric constant near the antiferromagnetic transition temperature (T_N ∼ 643 K) of BiFeO₃ indicates the existence of magneto-electric coupling in this composite. Magnetocapacitance (MC) of 0.3NiFe₂O₄ – 0.7BiFeO₃ composite was measured at room temperature and the MC values of 13.5% and 7.8% (at 5000 Oe) are observed when the pellet is perpendicular and parallel to the magneticfield direction respectively. The presented magnetic and dielectric studies reveal the existence of magnetoelectric coupling and spin glass frezing of 0.3NiFe₂O₄ – 0.7BiFeO₃ nanocomposite.