Enhanced electromagnetic wave attenuation in Ca-substituted DyFeO3 orthoferrites: role of defect engineering and magnetic resonance

Abstract

The development of lightweight and high-performance microwave absorbing materials has become increasingly important owing to the rapid expansion of wireless communication systems and the growing demand for effective electromagnetic interference (EMI) shielding. Rare-earth orthoferrites have emerged as promising candidates because of their remarkable magnetic ordering, structural stability, and tunable dielectric properties. In this study, Dy_1-xCa_xFeO₃ (x = 0 to 0.3) ceramics were synthesized by improved sol–gel method to investigate the influence of Ca²⁺ substitution on their structural, vibrational, magnetic, and microwave absorption characteristics. X-ray diffraction confirmed the formation of a single-phase orthorhombic perovskite structure (Pbnm) without detectable secondary phases, demonstrating that Ca substitution preserves the structural integrity of DyFeO₃. The crystallite size remained within the nanometer range, while slight variations in lattice strain reflected local structural distortion induced by aliovalent substitution. Raman spectroscopy revealed systematic modifications in the A_g and B_2g phonon modes, indicating changes in FeO₆ octahedral distortion and lattice dynamics. FESEM analysis showed densely packed polycrystalline particles with average particle sizes increasing from approximately 271 to 392 nm as the Ca content increased. Magnetic measurements demonstrated enhanced ferromagnetic behavior resulting from modified Fe–O–Fe exchange interactions and spin canting. The complex permittivity and permeability measured in the 2–18 GHz frequency range revealed improved dielectric polarization, magnetic relaxation, and impedance matching after Ca substitution. Among all compositions, Dy_1-xCa_xFeO₃ (x = 0.1) exhibited the strongest microwave absorption; achieving a minimum reflection loss of approximately −34 dB near 12 GHz. Cole–Cole analysis confirmed multiple non-Debye relaxation processes associated with interfacial polarization, oxygen vacancies, and Fe³⁺/Fe⁴⁺ electron hopping. The synergistic interaction between dielectric loss, magnetic loss, and optimized impedance matching significantly enhances microwave attenuation, highlighting Dy_1-xCa_xFeO₃ (x = 0.1) as a promising material for electromagnetic interference shielding and microwave absorption applications.