Magnetic anisotropy of polycrystalline magnetoferritin investigated by SQUID and electron magnetic resonance

et al.Magnetoferritin molecules with an average inorganic core diameter of 5.7±1.6 nm and polycrystalline internal structure 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 seconds to nanoseconds. In addition, angle-dependent EMR experiments were carried out for the determination of the nanoparticle symmetry and internal magnetic field. Due to the large surface to volume ratio, the nanoparticles show larger and uniaxial rather than cubic magnetic anisotropies compared to bulk maghemite and magnetite. © 2014 Elsevier B.V.We acknowledge funding from the Marie Curie Intra European Fellowship PIEF-GA-2009-253980 (F.M.), EPSRC National UK EPR Facility and Photon Science Institute of the University of Manchester, Spanish MICINN under Grants MAT2012-38318-C03-01 and MAT2012-38318-C03-03 and from DGA, under Grants Biología Estructural and MOLCHIP. AL thanks ARAID for financial support. RdM and MJ are indebted to MICINN and CSIC for receiving pre-doctoral FPU and JAE fellowships, respectively.Peer Reviewe