Influence of annealing on magnesioferrite nanoparticles synthesized by a sol-gel/combustion method

Abstract

to 200 °C for 20 minutes so that auto-combustion would take place. Finally, the product was annealed in a furnace for 2 hours at different temperatures. MeasurementsX ray diffraction patterns were obtained using an XPert Pro Panalitical diffractometer with Cu Kα radiation (λ = 1.5418 Å). The average particle size was calculated from line broadening using the TOPAS application 3 , academic edition. Mössbauer spectra were recorded at several temperatures between 25 K and room temperature in a homemade instrument using a source of 57Co(Rh) with an activity of about 50 mCi. Table 1 shows the average particle sizes, as calculated from the X ray spectra shown in Figure 1, for samples as prepared and after annealing at three different temperatures. Experimental Results and AnalysisThe Mössbauer spectra of sample 2 in Table 1 are shown in Figure 2 for several different measurement temperatures. While at room temperature there is a doublet due to superparamagnetic relaxation, at lower temperatures one sees a sextet which is characteristic of bulk magnesioferrite 4 . By taking the ratio of the area under the doublet to the area under the sextet, it is possible to estimate the volume fraction of unblocked particles for each measurement temperature. The IntroductionNanosized ferrites display physical and chemical properties which may be quite different from those of their bulk counterparts. Magnesioferrite (MgFe 2 O 4 ) is one of the most interesting, because, due to its small magnetocrystalline anisotropy, superparamagnetic properties are still present at relatively low temperatures and/or high magnetic fields. The purpose of this work was to investigate the influence of annealing on the average particle size and particle size distribution of MgFe 2 O 4 nanoparticles prepared using the sol-gel/ combustion method 1 , a fast and relatively inexpensive technique. The average particle size was determined by X ray diffraction, while the particle size distribution was obtained by measuring at several temperatures the relative intensity of the Mössbauer spectra due to superparamagnetic particles and to ferrimagnetic particles, a method that has already been applied successfully 2 to another nanosized ferrite, CoFe 2 O 4 . O, and annealed for 2 hours at 400, 500 and 600 °C. The average particle size, determined by X ray diffraction, was found to depend on the annealing temperature and varied from 〈D〉 = 8.1 to 〈D〉 = 17.8 nm. By measuring at several temperatures the relative intensity of the Mössbauer spectra due to superparamagnetic particles and to ferrimagnetic particles, we determined the size distribution of the nanoparticles in the samples. It was found to be a log-normal distribution with a most probable diameter that varied from Dm = 6.4 to 17.2 nm and a full width at half-height ∆D in the 5-6 nm range. Experimental Procedure Sample preparation

Structural and Magnetic Studies on Iron Oxide and Iron-Magnesium Oxide Thin Films Deposited Using Ferrocene and (Dimethylaminomethyl)ferrocene Precursors

“…27 In addition, if the stoichiometry of the films were close to that of magnesioferrite MgFe 2 O 4 , then some significant peaks would also overlap with those of magnetite. For instance, locations of strong 220, 311 and 400 reflections of both MgFe 2 O 4 (PDF card 017-0464) 57 and magnetite are identical. Distinction between maghemite, magnetite and magnesioferrite phases may be possible by XRD, 27 but remains complicated.…”