Modulated magnetic property, enhanced microwave absorption and Mössbauer spectroscopy of Ni0.40Zn0.40Cu0.20Fe2O4 nanoparticles embedded in carbon nanotubes

Nanoparticles of Ni0.40Zn0.40Cu0.20Fe2O4 were prepared by sol-gel method where ultrasonication was applied to reduce the distribution of sizes as well as the agglomeration among the nanoparticles. The as dried sample was annealed at 100 and 300 °C. To modulate the soft magnetic property and also to enhance the microwave absorption in X and Ku bands of microwave frequencies, the prepared nanoparticles of each annealed sample were incorporated in the non-magnetic matrix of multi-walled carbon nanotubes (CNTs). The formation of the crystallographic phase of the bare and encapsulated samples was confirmed by X-ray diffractograms. The Raman spectra of the samples were recorded at room temperature and the observed characteristic peaks also confirmed the presence of individual component of NZCF and CNT in the nanocomposite sample. The average nanocrystallite size of NZCF sample was calculated from the broadening of the (3 1 1) peak in the XRD pattern using the Debye-Scherrer formula. The average particle size, crystallographic phase, etc., of one selected sample obtained from the high-resolution transmission electron microscopy is in good agreement with those estimated from the XRD patterns. The observed micrographs in transmission electron microscopy confirmed that the nanoparticles of NZCF were encapsulated in the matrix of CNT. The dynamic and static magnetic properties were measured by digital hysteresis loop tracer and SQUID magnetometer. Different magnetic quantities viz., saturation magnetization, coercive field, saturation to remanence ratio, etc., of the samples were also extracted and these extracted values confirmed the presence of mixed state of superparamagnetic and ferrimagnetic nanoparticles. Reflection losses of the samples in different bands (X and Ku) of microwave region of frequency were measured by vector network analyzer. Interestingly, the microwave absorption is significantly enhanced compared to that of the individual component of the nanocomposite sample. Mössbauer spectra of the samples were also recorded at room temperature (300 K) and the observed spectra also confirmed the presence of superparamagnetic and ferrimagnetic particles in the mixed state of the nanocomposite samples.