Dielectric properties of superparamagnetic titanium doped nanophased Mn–Zn ferrites for high frequency applications

Effect of Ti⁴⁺ ions on Structural, Dielectric and Magnetic properties of nanophasedMn_0.5Zn_0.5Ti_xFe_2–4x/3(x = 0.0, 0.01, 0.02,0.03, 0.04 and 0.05) ferrites synthesized by hydrothermal method is studied. XRD peaks reveal pure spinel phase without extra peaks. Lattice parameter (a) is found to vary non-linearly with dopant concentration (x). An overall decrease in Crystallite Size (D) (varying from 78 nm–41 nm) with x is witnessed. Values of dielectric constant (${\epsilon }^{\prime }$) and loss factor (tan δ) of Ti⁴⁺ doped Mn–Zn ferrites are lower than that of the undoped sample. Increase of AC resistivity (ρ) by an order of 10 in Ti⁴⁺ doped Mn–Zn ferrites is ensued due to locking of Ti⁴⁺–Fe²⁺ pairs. Lowered values of M_s is attributed to spin canting due to growth of nanosized grains, weakening of exchange interactions by non-magnetic Ti⁴⁺ doping and lower values of x-ray density. Transition from single to multi- domain region of Mn–Zn–Ti ferrites is clearly evinced from the plot of Coercivity (H_c) with D. Reduced value of coercivity to zero upto a critical size of ∼49 nm indicates the existence of superparamagnetism in these ferrites. Superparamagnetismis first ever reported in the present caseof Ti⁴⁺ doped Mn–Zn ferritessynthesized by hydrothermal method. Relatively lowered values of ${\epsilon }^{\prime }$ (29–18), tan δ (of the order of 10^–2–10^–3), higher values of ρ (10⁶ Ω—cm) and lowered values of H_c obtained with Ti⁴⁺ doping improve the eddy current losses and direct these materials for high frequency applications. (paper)