| Abstrakt: |
Maghemite (γ-Fe2O3) nanoparticles were synthesized via a sol–gel process with (Fe(NO3)3 9H2O) as a starting material and annealed in an Ar/H2 (5%) balanced gas atmosphere. According to x-ray analysis, the average particle size was found to be 7.0 nm with a narrow size distribution for samples annealed at 150°C. Transmission electron microscopy (TEM) analysis also confirmed a particle size of 7.2 nm. The structural and magnetic properties were analyzed using x-ray diffraction (XRD), vibrating-sample magnetometry (VSM), and Mössbauer spectroscopy, and were found to have a spinel structure and exhibit superparamagnetic behavior. TEM was carried out to monitor the size and morphology of the particles. The hyperfine fields at 4.2 K for the A and B sites were determined to be 509 kOe and 476 kOe, respectively. The isomer shift values were δB = 0.36 mm/s and δA = 0.32 mm/s, which both correspond to Fe3+. Since magnetite (Fe3O4) has Fe2+ and maghemite has only Fe3+, it can be seen from the Mössbauer result that the powder heat-treated at 150°C is maghemite. The blocking temperature (TB) of the superparamagnetic maghemite nanoparticles was approximately 167 ± 5 K. The magnetic anisotropy constant was calculated to be 1.4 × 106 ergs/cm3. The coercivity value at 0 K was calculated as HCO = 174.5 Oe. [ABSTRACT FROM AUTHOR] |
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