Electron paramagnetic resonance ͑EPR͒ in iron-oxide nanoparticles ͑ϳ2.5 nm͒ embedded in a polyethylene matrix reveals the sharp line broadening and the resonance field shift on sample cooling below T F Ϸ40 K. At the same temperature a distinct anomaly in the field-cooled magnetization is detected. The temperature dependences of EPR parameters below T F are definitely different than those found for various nanoparticles in the superparamagnetic regime. In contrast to canonical bulk spin glasses, a linear fall-off of the EPR linewidth is observed. Such behavior can be explained in terms of the random-field model of exchange anisotropy.
Articles you may be interested inSize dependent ferromagnetic resonance and magnetic anisotropy of hexagonal barium and strontium ferrite powders Low temperature electron paramagnetic resonance anomalies in Fe-based nanoparticles Three types of iron-based oxide nanoparticles ͑weight compositions Fe 2 O 3 , BaFe 2 O 4 , and BaFe 12 O 19 ) embedded in a polyethylene matrix are studied using the electron paramagnetic resonance technique. All nanoparticles are found to be multiphase. Thermal variations of electron paramagnetic resonance spectra reveal the presence of two phases in the Fe 2 O 3 nanoparticles. One such phase undergoes an antiferromagnetic-like transition near 6 K. Nanoparticles of BaFe 2 O 4 demonstrate a resonance anomaly near 125 K that could indicate the presence of a magnetic phase. Reduced magnetic anisotropy in BaFe 12 O 19 nanoparticles may be related to either structural imperfection or particle smallness ͑effective diameter of less than 10 nm͒. Our data clearly show that low temperature experiments are desirable for the correct identification of nanoparticles by means of the electron paramagnetic resonance technique.
Articles you may be interested inTemperature dependence of electron magnetic resonance spectra of iron oxide nanoparticles mineralized in Listeria innocua protein cages A study of the electron paramagnetic resonance of Fe-based nanoparticles embedded in polyethylene matrix was performed as a function of temperature ranging from 3.5 to 500 K. Nanoparticles with a narrow size distribution were prepared by the high-velocity thermodestruction of iron-containing compounds. A temperature-driven transition from superparamagnetic to ferromagnetic resonance was observed for samples with different Fe content. The unusual behavior of the spectra at about 25 K is considered evidence of a spin-glass state in iron oxide nanoparticles.
Nanocomposites of high-pressure polyethylene and zinc oxide nanoparticles are synthesized through thermal decomposition of zinc acetate. The phase composition of the nanocomposites is determined by x-ray diffraction (XRD), and the average size of ZnO nanoparticles is evaluated by transmission electron microscopy. The average size of the nanoparticles varies from 1 to 10 nm, depending on the ZnO content of the material. Both XRD and EXAFS results indicate that the zinc oxide nanoparticles have the wurtzite structure.
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