LAUSR

Abstract This study explore the influence of 10% Li doping on the crystallography, cation distribution, morphology, optical and magnetic properties of middle range Cobalt–Zinc nanoferrites. Single-phase intrinsic quaternary Co0.4+xZn0.6-xFe2O4 (x = 0.0, 0.1 and 0.2) and 10% Li doped quinary Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites with average crystallite size in the 13–34 nm range were synthesized through sol-gel auto-combustion method. Rietveld profile refinement of the PXRD patterns, presence of fcc rings in the SAED patterns and observation of active Raman modes illustrated single phase formation of mixed spinel nanoferrites in the fcc structure without impurity. In these nanoferrites Zn2+ ions preferentially occupy the tetrahedral site and Co2+ & Li1+ ions occupy the octahedral site with total preference. Both intrinsic quaternary and Li doped quinary nanoferrites significantly absorbs optical light in the UV band. The band gap energy decreases with decreasing Zn concentration and Li doping in these nanoferrite leads to blue shift of more than 1eV in the band gap energy. Co0.4+xZn0.6-xFe2O4 (x = 0.1 and 0.2) and Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites exhibited S-shape ferrimagnetic hysteresis loops at 300 K, 200 K, 100 K & 20 K. The Co0.4Zn0.6Fe2O4 nanoferrite display superparamagnetism at 300 K with a blocking temperature at 183 K. Systematic enhancement in the saturation magnetization (Ms), coercivity (Hc), remanence (Mr) and squareness ratio with lowering the temperature in these nanoferrites revealed conversion of soft-ferrimagnetic to hard-ferrimagnetic character. 10% Li doping in these nanoferrites resulted in significant enhancements of the Hc, Mr and TB. Monotonic increase in the Ms, Hc, Mr and TB has also been observed with the decreasing Zn concentration in these nanoferrites. Rich magneto-optical properties of quinary Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites can find applications in the design and fabrication of magneto-optic and permanent magnet based devices.