Correlation between the magnetic-microstructure and microwave mitigation ability of MxCo(1−x)Fe2O4 based ferrite–carbon black/PVA composites

Abstract

A study of controlling the microwave mitigation properties of ferrite–carbon black/PVA composites by tuning the magnetic microstructure and spin arrangement of the ferrite particles is presented. M_xCo_(1−x)Fe₂O₄ (M: Ni²⁺, Mn²⁺ & Zn²⁺) nano-ferrites (NFs) were synthesized by a solvothermal method and these NFs were used to fabricate NF–CB hybrids and flexible NF–CB/PVA composite films. The magnetic force microscopy studies of the NFs reveal a unique single axis oriented domain structure for Zn-NFs and multi-domain magnetic microstructures for Mn-NFs and Ni-NFs. Mössbauer analysis of the NFs reveals highly distorted co-ordination of Fe³⁺ cations in Zn-NFs, whereas sub-lattice spins are canted in Mn-NFs and Ni-NFs. Despite the distorted magnetic lattice and broken coordination, the largest microwave shielding effectiveness (SE) of 32 dB is observed, over a bandwidth of 8 to 18 GHz, for Zn-NF–CB/PVA with a major contribution from absorption (SE_A ∼ 25 dB). The dielectric properties and Cole–Cole plots indicate enhanced interfacial polarization in Zn-NF–CB/PVA, which is attributed to the motion of polarons across multiple heterogeneous interfaces. These polarons are thought to be generated by distorted co-ordination of Fe³⁺, and d–d electron transition between Co²⁺ Fe³⁺ cations at the B-site of Zn-NF. Distorted co-ordination of Fe³⁺ in Zn-NF along with unique single axis oriented magnetic domains play a crucial role in magnetic losses, as μ′′ is almost double in Zn-NF based composites as compared to other composites. Due to their excellent and tunable microwave absorption properties, NF–CB/PVA composites could be employed for next generation stealth applications.