Nanoporous Ni_0.5Zn_0.5Fe₂O₄ particles of diameter, ∼ 9.5 nm, were synthesized by citric acid assisted thermal decomposition in an autoclave. The BET surface area measured was 80 m² g^-1 and the average pore diameter was 2.5 nm. By soaking the particles in a suitable precursor solution and then subjecting them to a heat treatment at 923 K for 3 h, Pb(Zr_0.52Ti_0.48)O₃ was grown within the nanopores. X-ray and electron diffraction studies confirmed the presence of both these phases. The nanocomposites showed ferromagnetic behaviour over the temperature range 2–300 K. No ferroelectric hysteresis loop could be found which was consistent with the earlier theoretical prediction of loss of ferroelectricity below a critical thickness of 2.4 nm. Good magneto-dielectric response of the order of 7% at a magnetic field of 9 kOe was recorded for the present system. This is believed to arise due to a negative magnetostriction coefficient of Ni_0.5Zn_0.5Fe₂O₄ which exerted a compressive strain on Pb(Zr_0.52Ti_0.48)O₃ thereby lowering the tetragonality in its crystal structure.

Composites comprising of nanoparticles of Ni_0.5Zn_0.5Fe₂O₄ (NZF) and BaTiO₃ (BT), respectively were synthesized by a chemical method. The particles had diameters in the range of 15–31 nm. NZF was prepared by a coprecipitation technique. This was soaked in a sol containing BT. Compositions synthesized were 𝑥NZF-(1 - 𝑥) BT, where 𝑥 = 0.7, 0.5 and 0.3, respectively. The composites showed ferromagnetic hysteresis loops due to NZF phase. The analysis of coercivity variation as a function of temperature gave blocking temperatures in the range of 306–384 K depending on the diameter of the ferrite nanoparticles. This implied that superparamagnetic interactions are above these temperatures. The nanocomposites also exhibited ferroelectric behaviour arising due to the presence of BT. The remanent polarization of the samples was small. This was adduced to the nanosize of BT. The specimens showed magneto-dielectric (MD) effect in the magnetic field range 0–0.7 Tesla. The MD parameter measured at the maximum magnetic field was around 2\%. This was one order of magnitude higher than that reported so far in similar composite systems. This was explained on the basis of a two-phase inhomogeneous medium model with an interface between them, the phases possessing drastically different electrical conductivities.