Room temperature ferromagnetism in Mn-doped NiO nanoparticles

• Mn-doped NiO nanoparticles are prepared by a simple hydrothermal method.
• Unit cell volume decreases with increasing doping concentration.
• Mn-doping leads to room temperature ferromagnetism in NiO nanoparticles.
• Magnetization is highest for 2% Mn-doping.
• Above 2%, magnetization decreases with increasing doping.

Mn-doped NiO nanoparticles of the series Ni1−xMnxO (x=0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m. Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum.