Room temperature ferromagnetism in Zn-doped NiO nanoparticles: An experimental and DFT+U approach

Abstract

Abstract We report the room temperature ferromagnetism in Zn-doped NiO nanoparticles of Ni1−x ZnxO (x = 0.00, 0.01, 0.03, 0.05 and 0.1) prepared by the sol-gel method. Zn dopant has significant influence on structural, optical, and magnetic properties of NiO crystal when there is a size reduction and lattice distortions. The crystalline nature of the samples were characterized by the room temperature X-ray Diffraction and we found that the range of crystallite size is about 7 ± 0.01 to 9 ± 0.01 nm for 3–10% of Zn doping concentration. The lattice parameter and the effective strain increases with the increase of doping concentration. Local structure and defects are probed through Raman characterization which reveals that there are no secondary or impurity peaks on the Zn-doped NiO samples. Photoluminescence spectra at room temperature shows two major emission peaks at wavelength 357 nm and 393 nm for both pure and Zn-doped NiO powder respectively. There also exists a blue shift for wavelength 357 nm emission band with the increase of Zn doping concentration. The band gap energy calculated from the PL spectra is ≈3.46 eV for pure NiO and it increases with the doping upto 3% then it decreases with further doping. To understand the effect of doping on magnetic properties, we measured the temperature dependent M-H loops and M-T curve for zero field cooled (ZFC) and field cooled (FC) condition in the temperature range 25–350 K using Vibrating Sample Magnetometer. We observed that the Ni1−x ZnxO nanoparticles are ferromagnetic in nature at room temperature with highest magnetic moment of ≈1.9 emu/g when the doping of Zn is 3% and it decreases with further increase of doping concentration. M-T data bifurcation peak was observed around 300 K and a broad peak in ZFC curve below the bifurcation. This broad peak is attributed to the thermal relaxation of uncompensated spins. We have also investigated the first-principle DFT+U calculation to study the electronic properties of the materials. The results show that the Zn-doped NiO with oxygen vacancies are ferromagnetic in nature whereas without defects the compound is non-magnetic, which agrees quite well with the experimental results. The nanoparticle with ferro-magnetic properties have potential application in the field of nanomagnetism and also its optical properties could be useful for optical device applications.