La³⁺ Modulated Cu₀.₅Co₀.₅Fe₂₋ₓLaₓO₄ Spinel Ferrites: Structural, Magnetic, and Temperature-Dependent Dielectric Spectroscopy for Microwave Absorption and Dielectric Device Applications

Abstract

La³⁺ modulated Cu₀.₅Co₀.₅Fe₂₋ₓLaₓO₄ (x = 0.16 and 0.20) spinel ferrites were synthesized and their structural, magnetic, and dielectric properties were investigated for microwave absorption and dielectric device applications. XRD analysis confirmed the formation of a single-phase cubic spinel structure (Fd-3m). The lattice constant increased slightly from 8.355 Å to 8.359 Å, and crystallite size increased from 39.46 nm to 44.28 nm with La³⁺ substitution. Bertaut’s intensity ratio method revealed strong preferential occupancy of La³⁺ ions at octahedral [B] sites.VSM measurements showed a drastic reduction in saturation magnetization (Ms) from 37.8 emu/g (x = 0.16) to 1.94 emu/g (x = 0.20), with the magnetic moment (n_B) decreasing from 1.69 μ_B to 0.088 μ_B. Temperature-dependent dielectric spectroscopy at 100 Hz revealed a dielectric constant (ε′ ≈ 1.1 × 10⁶) and high dielectric loss (ε″ ≈ 28–30 × 10⁶) for x = 0.16, which decreased significantly to ε′ ≈ 1.3 × 10⁵ and ε″ ≈ 7–8 × 10⁶ for x = 0.20. The Curie temperature shifted from 290–310°C to 320–340°C with increasing La content. The suppression in magnetic and dielectric properties is attributed to the replacement of magnetic Fe³⁺ by non-magnetic La³⁺ ions at octahedral sites, weakening superexchange interactions and electron hopping. These results indicate that La³⁺ modulation effectively tunes the multifunctional properties of Cu-Co ferrites, making them promising for microwave absorption and dielectric device applications.