Unusual variation of blocking temperature in bi-magnetic nanoparticles

Ferrite nanoparticles with bi-magnetic layered structure were synthesized by a seed-mediated co-precipitation technique. The strategy of growing a second magnetic layer enhanced the magnetic saturation (Ms) of the nanostructures, with a very small increase in their blocking temperature (TB). In contrary to the common magnetic nanostructures of 10-15 nm size range, which manifest blocking temperatures around room temperature (≈300 K), the measured TB values of the bi-magnetic nanostructures are much lower. The experimental TB values of the bi-magnetic nanostructures are much lower than their theoretically predicted ones. Moreover, the TB of the nanoparticles varies unusually, decreasing with particle size beyond a certain value. The low blocking temperature and high Ms of the fabricated bi-magnetic nanoparticles indicate the seed-mediated coprecipitation is an effective method for designing magnetic nanostructures suitable for biomedical applications such as in magnetic hyperthermia treatment, where nanostructures of low TB and high Ms are required.