Electrical Behavior of Tb-Mn Substituted Y-Type Hexa-ferrites for High-Frequency Applications

Single phase nanostructured Tb-Mn substituted Y-type hexaferrites with composition Sr2Co2-x Mn (x) Tb (y) Fe12-y O-22 (x = 0.0-1, y = 0.0-0.1) have been synthesized by the normal microemulsion technique. X-ray diffraction patterns reveal the formation of Y-type hexagonal single phase. The crystallite size, calculated by Scherer's formula, is found in the range of 30-48 nm, which is well suitable for obtaining good signal-to-noise ratio in high density recording media. The enhancement in direct current resistivity has been attributed to the reduction in Fe3+ ions at octahedral sites. The Arrhenius plots show that there are two conduction mechanisms operating in the synthesized materials: in the ferri-region, the conduction is due to electrons, whereas in the para-region, it is due to polaron hopping phenomena. The calculated values of activation energy in the para-region are greater than 0.40 eV, which clearly suggests that the conduction phenomenon is due to hopping of polarons. Variation of dielectric constant with frequency depicts that the dielectric constant initially decreases with increase in frequency, while at higher frequency it decreases slowly. The dielectric results are in agreement with the Maxwell-Wagner model. Both the resonance and relaxation peaks at high frequency have been observed in dielectric loss and tan delta data. It has been noted that such types of peaks appear when hopping frequency becomes equal to that of the external applied field. The high values of resistivity and low dielectric loss make these materials best candidates for high frequency applications.