Defect-induced modulation of magnetic and dielectric properties in Co-doped NiO nanoparticles

In the hunt for room-temperature ferromagnetic oxide semiconductors, nanocrystalline Cobalt (Co) doped nickel oxide (NiO) samples were synthesized using chemical co-precipitation and analysed for their structural, optical, morphological, magnetic, and dielectric properties at varying cobalt concentrations (1%, 2%, and 3%). X-ray diffraction (XRD) analysis established a stable single-phase face-centered cubic (FCC) structure up to 2% Co doping, with the appearance of a secondary NiCo 2 O 4 spinel phase at 3%, signifying a threshold for phase stability. Optical absorption spectra exhibited transitions characteristic of Ni 2+ and Co 2+ , with minor shifts ascribed to cobalt ion influence on electronic structure. Surface morphology and chemical composition studies through SEM-EDAX exposed nanostructured samples with slight agglomeration that intensified as Co content increased. Magnetic measurements (VSM and SQUID) reveal predominantly paramagnetic behaviour with weak ferromagnetic contributions arising from defect-mediated interactions and Co-induced exchange modifications. Magnetization increases with Co doping; however, the absence of significant hysteresis and saturation indicates a dominant antiferromagnetic NiO matrix with weak ferromagnetic behaviour. The absence of significant long-range ferromagnetism can be attributed to the low charge carrier density and the dominant antiferromagnetic ordering. Dielectric studies revealed a decrease in the dielectric constant with increasing cobalt concentration, with values also showing temperature and frequency dependence, suggesting cobalt ion role in modifying the dielectric response. These findings illustrate that Co doping impacts both the structural integrity and functional properties of NiO, offering valuable insights for potential applications in electronic devices.