Synthesis and characterization of oleylamine capped MnxFe1-xFe2O4 nanocomposite: Magneto-optical properties, cation distribution and hyperfine interactions

Abstract

Abstract Pure Fe 3 O 4 NPs and Oleylamin (OAm) capped Mn x Fe 1-x Fe 2 O 4 (Mn x Fe 1-x Fe 2 O 4 @OAm) (0.2 ≤ x ≤ 1.0) nanocomposites (NCs) were synthesized by the polyol route. Lattice parameter increases with increasing Mn 2+ concentration, due to the respective larger ionic radius of Mn 2+ ion compared with the Fe 2+ ion. The VSM analyses revealed superparamagnetic characteristics of all samples. The extrapolated specific saturation magnetization (σ s ) values decreased from maximum 50.74 emu/g to minimum 15.34 emu/g by increasing Mn content. The particle size dependent Langevin function was applied to determine the magnetic particle dimensions (D mag ) between 9.10 nm and 21.50 nm. The observed magnetic moments of NPs and NCs are in range of (0.64–2.10) μ B and significantly less than 4 μ B of bulk Fe 3 O 4 . Magnetic anisotropy was determined as uniaxial and calculated effective anisotropy constants ( K eff ) are between 32.14 × 10 4 Erg/g and 8.71 × 10 4 Erg/g. The size dependent saturation magnetization suggests the existence of a magnetically dead layers around the magnetic cores for NCs between 0.72 nm and 1.29 nm. From 57 Fe Mossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Mn 2+ substitution have been determined. Although, the Mossbauer spectra for the sample x = 0.2 is composed of ferromagnetic sextets, paramagnetic doublet is also formed for other samples. The percent diffuse reflectance spectroscopy (DR %) and Kubelka-Munk theory were used to specify the optical properties. The estimated optical band gap ( E g ) values from Tauc plots are between 1.50 eV and 2.05 eV. Increasing Mn content in NCs increased the band gap at different magnitudes.