Effect of PVP Assisted Growth of α-Mn 2 O 3 Nanoparticles on the Structural, Microstructural, Magnetic and Optical Properties

Single-phase manganese oxide, α-Mn 2 O 3 , nanoparticles have been prepared successfully using different amounts of 2w/v% polyvinylpyrrolidone (PVP) via co-precipitation. The samples prepared with 1 ml, 2 ml, 5 ml and 10 ml PVP are represented as S1, S2, S3 and S4, respectively. The effect of PVP amount on the structural, microstructural, magnetic and optical properties was systematically investigated. Rietveld refinement of the x-ray diffraction patterns revealed the single-phase formation of α-Mn 2 O 3 nanoparticles. The average crystallite sizes of the particles was found to be minimum for S2 with lowest lattice parameter and highest strain. High-resolution field emission scanning electron microscopy confirmed the smallest size of S2 with spherical morphology and smooth surfaces. Energy dispersive x-ray spectroscopy and maps showed uniform distribution of the elements favouring the Mn 2 O 3 composition. Raman and Fourier transform infrared spectra displayed characteristic bands corresponding to α-Mn 2 O 3 . The magnetic susceptibility revealed the antiferromagnetic nature of α-Mn 2 O 3 nanoparticles with Néel temperature, T N ~ 80.6 K for S2. The increase in PVP amount above 2 ml increased the T N as well as the magnetic frustration. The band gap was found to be maximum (1.8 eV) for S2 nanoparticles. Briefly, the smallest size nanoparticles with spherical shape and smooth surfaces were obtained for 2 ml PVP with the lowest magnetic frustration and highest band gap indicating the optimum amount of PVP to be 2 ml. Thereby, the results have revealed the limiting behaviour of polyvinylpyrrolidone chains operating during synthesis.