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Structural and electrical properties of manganese doped cobalt ferrite nanoparticles.

M Z Ahsan, F A Khan*

The structural, electrical and magnetoresistive properties of manganese doped cobalt ferrite nanoparticles have been investigated through measurements of dc and ac magnetic properties. The samples were synthesized via standard solid state reaction route. The X-ray diffraction patterns confirm the formation of spinel structure of the synthesized samples. Field Emission Electron Microscopy (FESEM) is done to estimate the average particle size. The energy dispersion spectrum marks the presence of Co, Mn, Fe and O in the studied sample. The dielectric constant and impedance were measured in the frequency range 100 Hz to 120 MHz and temperature range 400oC to 1200oC. Frequency dependent dispersion exhibits an anomalous behavior in the range between 1 MHz and 10 MHz. A pronounced leftward shift of relaxation peaks in the dispersion observed in the loss factor tanδ curve. The fabricated nanoparticles have shown semiconducting behaviour at low frequency regime (100 Hz, 1 kHz and 10 kHz) but a purely insulating behaviour at higher frequency regime (100 kHz and 1 MHz) indicating a second order phase transition. The magnetoresistive properties of Co1.125Mn0.125Fe1.875O4 in particular is assumed to be originated from the localized electrons and the magnetoresistance decreases monotonically with increasing magnetic field and hence bears the signature of a semiconducting material. However comparing the transvers and longitudinal magnetoresistance of the material we found that both the magnetoresistive parameters are magnetic field dependent and thus presumed to be a signature of mixed metallic and semiconducting nature of the material.