Exploring the interplay of lattice distortion, magnetic ordering, and dielectric behavior in Dy₂NiFeO_6-δ synthesized...

Double perovskite oxides with the general formula A₂BB'O₆ are widely recognized for their rich multifunctionality arising from strong spin-charge-lattice coupling. In this work, we present the successful synthesis and comprehensive characterization of Dy₂NiFeO_6-δ, a cobalt-free double perovskite oxide, via a wet chemical sol-gel route. X-ray diffraction (XRD) patterns validate the formation of a monoclinic P2₁/n structure with lattice parameters (a = 5.396 Å, b = 5.635 Å, c = 7.4873 Å, β = 90.285°). Transmission electron microscopy (TEM) reveals agglomerated nanocrystalline particles, where agglomeration originates from high surface energy, and magnetic dipole-dipole interactions may further enhance clustering. X-ray photoelectron spectroscopy (XPS) confirms the presence of Dy³⁺, Ni²⁺, and Fe²⁺ oxidation states, indicating oxygen deficiency (δ ≈ 0.5). Dielectric measurements demonstrate a frequency-dependent decline in permittivity (10 Hz-5 MHz) due to interfacial polarization, while temperature-dependent studies (298-523 K) exhibit an increase in dielectric constant, associated with thermally activated dipolar alignment and relaxation behavior in dielectric loss. AC conductivity increases with increasing temperature, indicating a negative temperature coefficient of resistance and a charge transport mechanism dominated by hopping conduction with an activation energy of 0.16 eV. Magnetic studies reveal a Néel temperature of ~ 107 K, with features of weak ferromagnetism and a spin-glass-like transition emerging below ~ 50 K, driven by 4f-3d exchange interactions and spin canting. The interrelationship between structural, dielectric, and magnetic properties underscores the multifunctional nature of Dy₂NiFeO_6-δ. While direct magnetodielectric or magnetoelectric coupling measurements remain to be explored, the observed multifunctional behavior suggests that this material shows promise for future magnetoelectric and spintronic applications.