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- 저자 : Dusan Milivojevic (검색결과 1 건)
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Ultrasmall iron oxide nanoparticles: Magnetic and NMR relaxometric properties
Branka Babic-Stojic,Vukoman Jokanovic,Dusan Milivojevic,Miroslav Pozek,Zvonko Jaglicic,Darko Makovec,Natasa Jovic Orsini,Mirjana Markovic,Katarina Arsikin,Verica Paunovic 한국물리학회 2018 Current Applied Physics Vol.18 No.2
Ultrasmall iron oxide (USPIO) nanoparticles, with diameter mostly less than 3 nm dispersed in an organic carrier fluid were synthesized by polyol route. The evolution of ZFC-FC magnetization curves with temperature, as well as the shift of the ac susceptibility peaks upon changing the frequency, reveal that the nanoparticles in the fluid are non-interacting and superparamagnetic with the blocking temperature TB ~10 K. The M€ossbauer spectra analysis proposed the core/shell structure of the nanoparticles consisting of stoichiometric g-Fe2O3 core and non-stoichiometric shell. The nanoparticle surface layer has a great influence on their properties which is principally manifested in significant reduction of the magnetization and in a large increase in magnetic anisotropy. Magnetic moments do not saturate in fields up to 5 T, even at the lowest measured temperature, T ¼ 5 K. The average magnetic particle diameter is changed from 1.3 to 1.8 nm with increasing magnetic field from 0 to 5 T which is noticeably smaller than the particle sizes measured by TEM. The estimated effective magnetic anisotropy constant value, Keff ¼ 2 105 J/m3, is two orders of magnitude higher than in the bulk maghemite. Measurements of the longitudinal and transverse NMR relaxivity parameters on water diluted nanoparticle dispersions at 1.5 T gave the values r1 ¼ 0.028 mmol1 s1, r2 ¼ 0.050 mmol1 s1 and their ratio r2/r1 ¼ 1.8. Continuous increase of the T1-weighted MRI signal intensity with increasing Fe concentration in the nanoparticle dispersions was observed which makes this ferrofluid to behave as a positive T1 contrast agent.
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