Nanoparticles of Ni0.2Zn0.6Cu0.2Fe2O4
were prepared by the standard co-precipitation method. The formation of nanocrystalline
mixed spinel phase has been confirmed by x-ray diffractograms. The sizes of the
nanoparticles were estimated in the range 7–30 nm, which was confirmed by transmission
electron microscopy. Thermal variations of the real part of AC magnetic susceptibilities
measured from 450 K down to 80 K and Mössbauer effect measurements at room temperature
and down to 20 K clearly indicate the presence of superparamagnetic particles in all the
samples. Specific saturation magnetizations measured by VSM are found to increase
steadily with the increase of average particle size. The coercive field obtained from
low frequency measurements shows that in all the samples a small fraction of
particles is not relaxed within the measuring time. For samples showing a less
dominating superparamagnetic behaviour, AC magnetic susceptibility data showed the
expected increase of blocking temperature with increase in particle size. Magnetic
anisotropy energy constants of the nanoparticles were estimated from the blocking
temperature and the values cannot be directly correlated with their particle sizes.
Nanoparticles of LiZnCoFeO (LZC) were prepared by the sol-gel method and dried in a furnace at ∼200 °C. The dried sample was annealed at 500, 600, 700, and 800 °C for 5 h each. Rietveld analysis of X-ray diffraction patterns confirms the cubic Fd3̅m phase formation with lattice parameters ranged from 8.376 up to 8.390 Å and allows the crystallite sizes (d) to be estimated. To enhance microwave (MW) absorption as well as the effectiveness for hyperthermia treatment, nanoparticles are taken in the matrix of multiwalled carbon nanotubes (MWCNTs) and the morphology of the so-prepared samples (LZC@MWCNT) was studied by scanning electron microscopy and transmission electron microscopy analyses. Both static and dynamic magnetic properties were investigated on the samples of LZC nanoparticles and compared to those of the samples of LZC@MWCNT. The samples annealed at 500, 600, and 800 °C are excellent candidates in cancer treatment as ac magnetic heating analysis shows that the hyperthermia temperature (42 °C) was successfully achieved for an applied ac magnetic field of 420 Oe and 300 kHz frequency. MW absorption study also reveals that the samples of LZC@MWCNT could be used as a potential MW absorbing material for which a maximum reflection loss (R) of ∼-21 dB was achieved at a frequency of 15.27 GHz for only 1 mm layer thickness.
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