Influence of Milling Time on Structural and Electromagnetic Properties of Manganese Doped Cobalt Ferrite Nanoparticles

This paper reports on the electromagnetic properties of manganese doped cobalt ferrite nanoparticles, synthesized via solid state reaction route using the planetary ball milling technique at different milling time (8h and 12h)in order to tune the material for applications in high frequency as well as microwave devices. The XRD patterns show the cubic spinel structure of the material. The lattice constant along with other associated structural parameters are found to increase but the particle size to decrease with the milling time. The positive value of real part of permeability is found to increase with the increase of frequency for the sample of milling time 8h. But for the sample of milling time 12h, its negative value is observed below 2 kHz and after onwards it becomes positive. This negative value of real part is the signature of diamagnetic behavior at the low frequency regime, which is assumed to originate due to the dominance of antiferromagnetic effect of Mn2+ ions on the B site. The diamagnetic behavior may make this material suitable to be used in electromagnetic suppression or shielding devices. The real part e' of permittivity demonstrates the normal behavior for both the sample of milling time 8h and 12h below 2 kHz and 0.1 MHz respectively. The peaks at 8MHz for the sample of milling time 8h and at 1MHz for the sample of milling time 12h in the dispersion of its imaginary part e'' indicate the resonance condition for the respective sample at the higher frequency regime, which is assumed to be originated from the faster hoping of electrons between Fe2+ and Fe3+ in the B site. At the low frequency regime, the a.c resistivity decreases almost exponentially with the increase of frequency to a certain minimum value at 10 kHz and 1 kHz for the samples of milling time 8h and 12h respectively and after onwards it becomes almost independent of frequency. The structural correlation is analyzed with the Col-Cole plot where the single incomplete semicircle corresponds to the grain boundary resistance for 12h milled sample and double incomplete semicircles to both the grain boundary and grain resistances for 8h milled sample. Almost constant characteristic impedance implies that both the permeability and permittivity are of equal value for the sample of milling time 12h and its nearer-to-zero value of eddy current loss may make this material suitable to be used in the design of microstrip/patch antenna. However the linear variation of characteristic impedance with the frequency for the sample of milling time 8h implies the tuning effect of multilayer capacitance, which may make this sample to be integrated as tuner with the microstrip/patch antenna.