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

• Published in: Journal of alloys and compounds Vol. 638; pp. 188 - 196
• Main Authors: Jazirehpour, M., Seyyed Ebrahimi, S.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 25-07-2015
• Subjects: Anisotropy; Aspect ratio; Dielectric constant; Magnetic properties; Magnetite; Microwaves; Nanoparticles; Nanorods; Percolation; Permittivity; Spherical nanoparticles; Percolation; Magnetite; Aspect ratio; Spherical nanoparticles; Nanorods
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.03.021

•A low cost, high yield and large scale capable synthesis process was introduced.•The aspect ratios are controllable via pH value and precursors concentration.•The aspect ratio effects on EM and percolation properties was determined.•Magnetite nanorods showed high attenuation coefficients and loss potential.•RL of −40dB at 2GHz was observed for nanorods and nanospheres at 4 and 8mm.
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 −40dB at 2GHz with thicknesses of 4 and 8mm, 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.