Novel Cu-Fe codoped NiO nanocrystalline semiconductors with superior room-temperature ferromagnetism and high dielectric performance for spintronic devices

Nickel oxide (NiO) has the potential to be a p-type diluted magnetic semiconductor, but its limited room-temperature ferromagnetism (RTFM) and dielectric properties make it less useful. This study addresses these limitations by synthesizing pure NiO, Cu-doped NiO (Ni_0.95 Cu_0.05 O), and Cu-Fe codoped NiO (Ni_0.95 Cu_0.025 Fe_0.025 O) nanopowders using NaOH-assisted co-precipitation. Rietveld-refined X-ray diffraction (XRD) confirmed a cubic structure with lattice parameter changes, while scanning electron microscopy/transmission electron microscopy (SEM/TEM) revealed reduced crystallite sizes from 23 to 10 nm. X-ray photoelectron spectroscopy (XPS) confirmed Cu²⁺ and Fe³⁺ oxidation states and oxygen vacancies. The measurements showed that the codoped sample exhibited a colossal dielectric constant (ε′ >10⁵ at 50 Hz) and enhanced saturation magnetization (3.5 emu/g vs. 0.47 emu/g for pure NiO). These improvements arise from synergistic effects: Cu doping promotes oxygen vacancies for space-charge polarization, while Fe enables bound magnetic polarons (BMPs). Thus, Cu-Fe codoped NiO emerges as a prime candidate for spintronics and high-density energy storage applications.