Exploring the structural, magnetic, and dielectric features of Ba_0.4Sr_0.4Ca_0.2Al_0.5Dy_xFe_11.50-xO₁₉ ferrite nanoparticles

M−type Ba-Sr/Ca hexaferrite nanoparticles (Ba_0.4Sr_0.4Ca_0.2Al_0.5Dy_xFe_11.5-xO₁₉, 0.00 ≤ x ≤ 0.80) were synthesized via sol–gel auto-combustion. Incorporation of Dy³⁺ ions into the M−type hexaferrite lattice resulted in an apparent expansion of the unit cell, accompanied by a modest increase in crystallite size, primarily attributed to the substitution of Fe³⁺ (ionic radius = 0.645 Å) with the larger Dy³⁺ ions (ionic radius = 0.912 Å). The preferential occupancy of Dy³⁺ at the octahedral B-sites played a crucial role in modulating magnetic exchange pathways, particularly enhancing Dy³⁺–O²⁻–Fe³⁺ superexchange interactions. This modification in local magnetic environments led to a significant enhancement in coercivity, with values spanning from 2000 Oe to 4500 Oe, thereby underscoring the material's viability for advanced permanent magnet and high-density magnetic recording applications. Moreover, Dy³⁺ substitution imparted favorable dielectric behavior, as evidenced by the suppression of both dielectric constant and loss tangent at elevated frequencies, highlighting their potential in microwave-frequency devices such as resonators, absorbers, and electromagnetic interference shielding components. These observations confirm that rare-earth doping, specifically with Dy³⁺, serves as an effective strategy for tailoring the structural, magnetic, and dielectric characteristics of hexaferrites, positioning them as multifunctional candidates for next-generation electromagnetic technologies.