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The nano-crystalline particles of erbium-substituted Ni-Zn ferrites with compositional formula Ni 0.7 Zn 0.3 Er x Fe 2-x O 4 (x = 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) were synthesized by sol-gel autocombustion method using citric acid as a combustion agent. Samples were sintered at 500 k in a static air atmosphere. The structure and crystallite size were analysed from X-ray diffractogram and obtained data-revealing spinel phase formation in the range of nanometric crystallite size which is also confirmed through scanning electron microscopy. The crystallite size was found to decrease along with Er 3? dopant ranging from 26 to 15 nm. The lattice parameters were found to decrease with greater Erbium ion concentration. The spinel formation and the absence of the organic phase were monitored by using spectral analysis of Fourier transform infrared spectroscopy. Electrical and magnetic properties were analysed at room temperature. The dielectric and dielectric loss tangent studies at room temperature showed the high polarization effect at low frequencies and low at high frequencies. The AC conductivity studies were also confirmed and support the dielectric results and AC conductivity increased with frequency suggesting that the conduction mechanism is owing to small polaron hopping between cations. Various magnetic properties were investigated by using a vibrating sample magnetometer, the coercivity and magnetic remanence were decreasing with increasing Er 3? concentration, but the saturation magnetization results have fluctuated between 44 to 47 emu/g. The squareness ratio of all samples are ranging from 0.13 to 0.17 at room temperature which is less than 0.50 that indicates the multi-magnetic domain structure with uniaxial anisotropy.

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