Magnetic exchange coupling and effect of grain and grain boundaries on conduction mechanism of (MgFe2O4)100-x /(BaFe12O19)x nanocomposites

(MgFe2O4)100-x/(BaFe12O19)x, soft/hard nanocomposites (NCs) having different hard ferrite ratio i.e. x = 0, 25, 50, 75 and 100 have been synthesized via in-situ auto-combustion sol-gel method. XRD patterns ensured the co-existence of both hexaferrite and spinel ferrite phases without any impure phase and no significant difference in average crystallite size was observed. The FTIR and Raman spectra confirmed the fabrication of desired material without any impurity. The absence of blocking peak in the ZFC measurements revealed that the blocking tem-perature of these NCs lie above room temperature. The M -H loops taken at different temperatures resulted into single smooth curve indicating strong interphase exchange-coupling among hard-soft ferrite phases. The occurrence of shoulder peak in dM/dH versus H curve for molar ratio x = 50 is an indication of weak exchange coupling between the two phases. From modified Block's law fitting, the Block's constant (B) exponentially declined with the addition of hard phase that revealed higher value of exchange-coupling constant J. The complex impedance analysis (Nyquist/Cole-Cole plots) and its simulation using an equivalent model circuit revealed the major contribution of both grains and grin-boundaries toward the total conduction mechanism of the NCs. These findings indicate that the higher value of impedance makes these NCs favorable candidates for numerous technological areas like electromagnetic shielding and high band-pass filters.