Static and Dynamic Magnetic Characterization of DNA-Templated Chain-Like Magnetite Nanoparticles

Here, we report the synthesis of chain like magnetite (Fe3O4) nanoparticles of different sizes. Chainlike formation of the nanoparticles is obtained using DNA as the template material. Being a chainlike molecule, DNA directs the growth of the particles in its own direction. Particle size is varied from 7 to 17 nm simply by varying the duration of the addition of coprecipitating agent. FTIR study confirms the bonding between metal ions and the phosphate backbone of the DNA chain. DC magnetic measurements reveal the decrease in anisotropy energy with increasing particle diameter. Smaller values of saturation magnetization of the nanoparticles than those of the bulk value are due to the presence of the magnetic dead layer in the nanoparticles (magnetic core and nonmagnetic shell), but in our case, the shell thickness decreases with an increase in particle size, which is opposite in trend as reported by other authors. Dynamic ac susceptibility measurements for the smallest particles (d approximate to 7 nm) show Neel-Arrhenius dependence of the blocking temperature with varying excitation frequency.