Polarized neutron scattering study of hollow Fe3O4 submicron spherical particles

We report results of polarized small-angle and wide-angle neutron scattering experiments at T = 10 and 300 K for 420 nm-sized hollow Fe3O4 spherical particles. Each hollow particle is a mesocrystal, which is composed of small nanoparticles with nearly the same crystallographic orientation. Polarized neutron experiments allow us to evaluate magnetic correlations of parallel and perpendicular magnetization components with respect to magnetic field during magnetization process. Small-angle neutron scattering reveals that as the magnetic field decreases from a saturation field of 10 kOe, the perpendicular magnetization component maximizes around zero applied field, whereas the parallel component minimizes. This behavior was observed below and above Verwey transition temperature of -120 K. Calculations of neutron intensities for vortex structures suggest the reorientation of the vortex core towards the magnetocrystalline anisotropy axis from the magnetic field direction at low applied fields. Moreover, a magnetic domain length obtained from the wide-angle scattering is of the order of 30-40 nm and comparable to the size of the small nanoparticles forming a hollow sphere, suggesting that magnetic correlations within the small nanoparticles always retain during magnetization process.

Automated summary

We conducted polarized small-angle and wide-angle neutron scattering experiments on 420 nm-sized hollow Fe3O4 spherical particles. Each particle is a mesocrystal composed of small nanoparticles with the same crystallographic orientation. We used polarized neutron experiments to evaluate the magnetic correlations during magnetization process. Our results show that the perpendicular magnetization component maximizes around zero applied field, while the parallel component minimizes, both below and above the Verwey transition temperature. Our calculations suggest the reorientation of the vortex core towards the magnetocrystalline anisotropy axis at low applied fields. We also found that the magnetic domain length obtained from wide-angle scattering is comparable to the size of the small nanoparticles forming the hollow sphere, indicating that magnetic correlations within the nanoparticles retain during magnetization process.