Physico-Chemical nanomaterials science

Synthesis condition assisted control on structural, magnetic properties and bandgap of Ni nano ferrites
Verma, R.1, Kane S.N.1, Tatarchuk T.2,*, Deshpande, U. P.3
1 School of Physics, D.A. University, Khandwa Road, Indore 452001, India 
2 Chemistry Department, Vasyl Stefanyk Precarpathian National University, Ivano-Frankivsk, 76018, Ukraine, tatarchuk.tetyana@gmail.com
3 UGC-DAE CSR, Khandwa Road, Indore 452001, India

Spinel ferrites, display two inter-penetrating sub-lattices A (tetrahedral), B (octahedral), and exhibit tunable structural, magnetic properties, bandgap. Tuning of their properties can be successfully accomplished by synthesis conditions, composition, thermal treatment etc., are valuable for their usage of ferrites for microwave devices, hyperthermia: for cancer treatment, photo-catalysis: for water purification etc. In this work we report, sol gel auto-combustion synthesis of NiFe2O4: by microwave-assisted synthesis (S1), dry gel (S2), thermally annealed for two hours at 450 oC (S3), and at 550 oC (S4). AR grade citrate/acetate, nitrate pre-cursors, were used in synthesis. Cukα x-ray diffraction 'XRD', vibration sample magnetometery, Ultraviolet–visible (UV–Vis) diffuse reflectance data, were respectively used to compute structural, magnetic properties and bandgap. Scanning Electron Microscopy 'SEM', Energy Dispersive spectroscopy 'EDS' were used to get surface morphology, elemental analysis. Formation of spinel nano ferrite phase (grain diameter: 38.3  39.2 nm), with lattice parameter (0.8345  0.8352 nm) was confirmed by XRD, which also shows presence of Fe2O3 phase. Studies on samples S1 to S4 confirm following: i) systematic decrease of Fe3+ ion, with concurrent increase of Ni2+ ion population on B-site, and proportionate increase of Fe3+ ions, and decrease of Ni2+ ions on A site, leading to increase of degree of inversion  (0.60  0.82), variation of oxygen parameter u (0.3801 − 0.3809; ii) fine-tuning of bandgap between 1.39  1.68 eV, is of use for visible-light photo-catalysis for water purification, iii) agglomerated particles are seen in SEM images, EDS suggests proper stoichiometric ratio of all elements, iv) re-location of cations on A, B site, strengthening of AB, AA, and weakening of BB super-exchange interaction, and spin canting (32.7 o  51.0o) due to surface dead layer ( 2.09  3.18 nm) are collectively responsible for the modification of saturation magnetization Ms (32.4  73.664 Am2/kg, linearly increases with u), coercivity Hc. Bandgap linearly decreases with increasing: Ni2+ ions on A-site, u, and lattice parameter, whereas it increases linearly with . Information on the types of surface active centers is obtained by antistructure modeling.