Effect of aspect ratio on dielectric, magnetic, percolative and microwave absorption properties of magnetite nanoparticles

Fe3O4 nanoparticles with tunable aspect ratio and fixed diameter were synthesized through a hydrothermal process and consequent reduction under hydrogen flow. Static magnetic and microwave electromagnetic properties were measured and it was found that the aspect ratio plays an important role in the microwave dielectric properties, however, static magnetic and microwave permeability were also affected. The real part of the nanorods permittivity was increased 4 times, compared to those of the spherical nanoparticles. The coercivity of the nanorods enhanced because of the higher surface anisotropy and shape anisotropy. A shift of ferromagnetic resonance was observed in their microwave permeability. A significant percolative permittivity behavior was observed in the nanorods especially in their real part of permittivity while such a significant percolative behavior for the spherical nanoparticles was not observed. The nanorods and the spherical nanoparticles produced a reflection loss peak value of about −40 dB at 2 GHz with thicknesses of 4 and 8 mm, respectively. Altogether, with increase in the aspect ratio of the magnetite nanoparticles their microwave attenuation coefficient as their total loss potential increased while their impedance match decreased. This suggests that microwave absorbers with excellent absorption properties can be produced from high aspect ratio nanorods if their impedance matching can be improved.