Sinteza i magnetne osobine α-, γ- i ε- feri-oksidnih nanokompozita

Abstract

Cilj rada je sinteza nanokompozitnih uzoraka hematita, maghemita i ε-Fe2O3 i proučavanje njihovih magnetnih osobina. Uzorci su dobijeni sol-gel metodom koristeći tetraetilortosilikat (TEOS) kao prekursor amorfnog silicijum dioksida i gvoţĎe nitrat (Fe(NO3)3·9H2O, Aldrich 98%) kao prekursor feri-oksida. Kontrolišući uslove sinteze dobijeni su nanokompoziti sa različitim strukturama i magnetnim karakteristikama. Karakterizacija uzoraka je izvršena difrakcijom X-zraka, transmisionim elektronskim mikroskopom i SQUID magnetometrom. Ispitivanja DC magnetizacije i AC susceptibilnosti pokazala su tipično ponašanje superparamagnetnih sistema, kao što je postojanje i frekventna zavisnost temperature blokiranja, ireverzibilnost zero-field-cooled (ZFC) i field- cooled (FC) krivih, pojava magnetne histerezisne petlje ispod temperature blokiranja i superparamagnetizam iznad temperature blokiranja. Ispitivani nanokompoziti su pokazali promene u vrednosti koercitativne sile od 0 Oe (hematit i maghemit) do 17000 Oe (ε-Fe2O3), i promene u saturacionoj magnetizaciji od 3,5 emu/g (hematit) do 67 emu/g (maghemit). Nanočestice ε- Fe2O3 faze su direktno dobijene od nanočestica hematita koje su ţarene do temperature od 1050˚C. Razmatrana je uloga meĎučestičnih interakcija na magnetne osobine. Ovi rezultati su vaţni za proučavanja magnetnih osobina nanočestičnih sistema, kao za mnoge industrijske i biomedicinske primene.

The aim of this work was to synthesize hematite, maghemite and ε-Fe2O3 nanocomposites, and investigate their magnetic properties. The samples were obtained by sol-gel method using tetraethylorthosilicate (TEOS) as precursor of silica, and iron nitrate (Fe(NO3)3·9H2O, Aldrich 98%) as precursor of ferric oxides. By controlling the reaction conditions, it was possible to obtain the nanocomposites with different structural and magnetic properties. Samples were characterized by X-ray powder diffraction, transmission electron microscopy, and SQUID magnetometry. Investigation of the magnetic properties by DC magnetization and AC susceptibility measurements indicated behavior typical of a superparamagnetic systems, such as the existence and frequency dependence of a blocking temperature, irreversibility of the zero-field-cooled (ZFC) and field-cooled (FC) curves, emergence of magnetic hysteresis below the blocking temperature, and suprparamagnetism above the blocking temperature. The nanocomposites showed variation in the coercivity values from 0 Oe (hematite and maghemite) to 17000 Oe (ε-Fe2O3), and variation in the saturation magnetization from 3,5 emu/g (hematite) to 67 emu/g (maghemite). Nanoparticles of ε-Fe2O3 are directly acquired from nanoparticles of hematite by applying heat treatments at increasing temperatures up to 1050˚C. The role of magnetic interparticle interactions on the magnetic properties is discussed. These results are valuable for the study of the magnetic behavior of nanoparticle systems, as well as for use in many industrial and biomedical applications.