Influence of Structure and Oxidation State on Magnetic Properties of Sr1−x La x Fe12−x Co x O19 Nanoparticles Prepared by Sol–Gel Combustion Method

Abstract

Nanoparticles of Sr1−xLaxFe12−xCoxO19 (x = 0 to 0.2) hexagonal ferrite have been synthesized by the sol–gel method using citric acid to complex the ions, followed by an autocombustion reaction after annealing at 900°C for 2 h in air. The crystal structure, valence state, and morphology of the samples were studied by x-ray diffraction (XRD) analysis, synchrotron x-ray diffraction (SXRD), x-ray absorption near-edge spectroscopy (XANES), and scanning electron microscopy. Rietveld refinement of XRD and SXRD patterns revealed that single-phase SrFe12O19 was obtained for all samples; the La3+ ion preferentially occupies the 2d site, whereas the Co2+ ion preferentially occupies the 2a and 4f2 sites. XANES analysis results indicated presence of Fe2+ ion in the samples with x = 0.1, 0.15, and 0.2. The particles were single domain with size in the range from 50 nm to 80 nm. The magnetic properties of the hexaferrite samples (SrFe12O19) were significantly improved as a result of the appropriate La/Co substitution. The coercivity values at room temperature increased from 6.7 kOe to 8 kOe with increasing La/Co concentration from 0 to 0.2. Maximum saturation magnetization of 73 emu/g was achieved at La/Co concentration of x = 0.1.