Magnetic anisotropy of polycrystalline magnetoferritin investigated by SQUID and electron magnetic resonance
Magnetoferritin molecules with an average inorganic core diameter of 5.7 ± 1.6 nm were investigated by a combination of transmission electron microscopy, magnetic susceptibility, magnetization, and electron magnetic resonance (EMR) experiments.
The temperature and frequency dependence of the magnetic susceptibility allowed for the determination of the magnetic anisotropy on an experimental time scale which spans from second to nanosecond. In addition, angular dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal field.
Due to the internal disorder of nano-crystals grown into the protein cages and large surface to volume ratio, the nanoparticles show larger anisotropy with respect to the bulk maghemite and magnetite material and uniaxial symmetry