Magnetic domain interactions of Fe(3)O(4) nanoparticles embedded in a SiO(2) matrix

Currently, superparamagnetic functionalized systems of magnetite (Fe(3)O(4)) nanoparticles (NPs) are promising options for applications in hyperthermia therapy, drug delivery and diagnosis. Fe(3)O(4) NPs below 20 nm have stable single domains (SSD), which can be oriented by magnetic field application. Dispersion of Fe(3)O(4) NPs in silicon dioxide (SiO(2)) matrix allows local SSD response with uniaxial anisotropy and orientation to easy axis, 90° <001> or 180° <111>. A successful, easy methodology to produce Fe(3)O(4) NPs (6–17 nm) has been used with the Stöber modification. NPs were embedded in amorphous and biocompatible SiO(2) matrix by mechanical stirring in citrate and tetraethyl orthosilicate (TEOS). Fe(3)O(4) NPs dispersion was sampled in the range of 2–12 h to observe the SiO(2) matrix formation as time function. TEM characterization identified optimal conditions at 4 h stirring for separation of SSD Fe(3)O(4) in SiO(2) matrix. Low magnetization (M(s)) of 0.001 emu and a coercivity (H(c)) of 24.75 Oe indicate that the embedded SSD Fe(3)O(4) in amorphous SiO(2) reduces the M(s) by a diamagnetic barrier. Magnetic force microscopy (MFM) showed SSD Fe(3)O(4) of 1.2 nm on average embedded in SiO(2) matrix with uniaxial anisotropy response according to Fe(3+) and Fe(2+) electron spin coupling and rotation by intrinsic Neél contribution.