Synthesis and characterization of tunable double-negative Cu/YIG nanocomposites for microwave and high-frequency applications

This study investigates the structural and electromagnetic behavior of copper-doped yttrium iron garnet (Cu/Y₃Fe₅O₁₂, Cu/YIG) nanocomposites synthesized via an in-situ solid-state route with Cu contents of 5–25 wt%. Structural characterization by XRD, FESEM, EDS, FTIR, and BET confirms that Cu incorporation progressively modifies the crystallite size, induces lattice distortion, and reshapes the surface morphology and porosity. Higher Cu loading increases the specific surface area and improves interfacial uniformity. The electromagnetic performance was evaluated in the low-frequency range (up to 100 MHz) using parallel-plate capacitance and inductance measurements, and in the 1–12 GHz microwave band using a rectangular waveguide transmission/reflection method (WR-90); the complex permittivity and permeability were extracted via the Nicholson–Ross–Weir (NRW) algorithm using samples with a thickness of 4.0 mm. The CY25 composite exhibits near-zero permittivity (ε′ ≈ 0) and pronounced negative permeability (μ′ < 0) in the 5–8 GHz region, driven by interfacial polarization, conductive network formation, and Cu-induced magnetic resonance. To the best of our knowledge, this work provides the first systematic correlation between the microstructural evolution of in-situ synthesized Cu/YIG nanocomposites and their tunable dual-negative and near-zero electromagnetic response in the 1–12 GHz microwave band. The results demonstrate that Cu acts as both a structural and functional modifier, enabling composition-dependent control over electromagnetic parameters. These insights establish a framework for designing scalable Cu-based metamaterials for applications in electromagnetic shielding, microwave electromagnetic response, and antenna technologies.