Tuning magnetism in 0.25BaTiO3-0.75CoFe2O4 hetero-nanostructure to control ferroelectric polarization

In multiferroic composites, the strain-mediated magnetoelectric coupling is strongly dependent on the characteristics of interface between two (ferroelectric/ferromagnetic) mechanically coupled phases. In this paper, we have studied the magnetic ordering in 0.25BaTiO₃-0.75CoFe₂O₄ (BTO-CFO) nanoparticles and the results are compared with pure CoFe₂O₄ (CFO) nanoparticles. The cubic spinel structure of CFO and tetragonal BTO is analyzed with X-ray diffraction pattern. The magnetic hysteresis measured at room temperature for both multiferroic BTO-CFO and pure CFO are quite different, that indicate magnetic ordering, which in BTO-CFO composite is changeable. Comparatively higher coercivity in pure CFO than BTO-CFO nanoparticles is observed at room temperature which suggested freezing out of thermal excitations and the onset of stable ferromagnetic ordering. The value of blocking temperature (corresponding to superparamagnetic state), T_B is 385 K is observed in pure CFO and 355 K of BTO-CFO. However, the magnetic curve of zero field cooling magnetization is reasonably different than that observed in pure CFO, which is further studied with frequency dependent ac magnetic susceptibility measurement. It results into spin-canting and spin-glass states formation. The spin-glass transition temperature is calculated with both dynamical scaling and Vogel-Fulcher methods. The ferroelectric hysteresis is observed at room temperature is reasonably varied with applied magnetic field of 2, 4, 5, 6 kOe and the variation in the values of polarization and coercive field might be consistent with the observed magnetic hysteresis.