Magnetic properties of MnFe2O4 nano-aggregates dispersed in paraffin wax

●MnFe2O4/paraffin nano-sized samples with different paraffin/ferrite ratios were prepared.●The samples were superparamagnetic at room temperature.●Bonding between paraffin molecules and surface atoms of ferrite particles reduced the surface spin disorder of nanoparticles.●The blocking temperature increased with increasing the paraffin concentration is the samples.

Manganese ferrite, MnFe2O4 nanoparticles with average size of ∼6.5 nm were synthesized by using a thermal decomposition method. The nanoparticles were aggregated which was confirmed by FESEM and TEM images. The aggregates with a diameter of ∼50 nm showed interacting superspin glass (SSG) behavior. The powders were dispersed in the molten paraffin wax by using ultrasonic bath. Samples with different paraffin/ferrite weight ratios of P/F= 0, 1, 5, 10 and 20 were prepared. M–H curves of the samples revealed presence of superparamagnetic state at 300 K. Saturation magnetization (Ms) decreased from 26.6 to 1.3 emu/g by increasing the P/F value from 0 to 20, respectively. Furthermore, the VSM measurements showed a decrease in surface spin disorder of paraffin-embedded nanoparticles in comparison with bare particles. The AC magnetic susceptibility peak temperature, TP increased from 230 to >300 K with increasing the paraffin content in the samples. The present study showed that by dispersing the particles in a non-magnetic matrix, the blocking temperature could be increased.