Study of Rare Earth and Transition Metals co-substituted Y-type Hexaferrites for high Frequency Applications

Abstract

The effects of rare-earth (Nd, Gd, Dy, Pr) and transition metal (Ni, Co) ions on Sr-Ba-Cu and Sr-Ba-Zn based Y-type hexaferrites have been investigated. Four series having nominal composition (1) SrBaCu2-xNixNdyFe12-yO22 (2) SrBaCu2-xCoxGdyFe12-yO22 (3) SrBaZn2-xCoxDyyFe12-yO22 and (4) SrBaZn2-xNixPryFe12-yO22, with x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0 and y=0.0, 0.02, 0.04, 0.06, 0.08, 0.1. Sol gel auto-combustion route was employed to prepare these four series. Thermal analysis was employed to study the thermal decomposition process and showed that the pure hexagonal phase was developed after annealing at 950 °C. The crystallite size obtained for all the samples was in the range of 11-22 nm. There was overall increase in lattice parameters by doping with rare-earth and transition metal ions. However, the increase was non-linear. The non-linear trend in lattice parameters was due to the large ionic radii of dopant cations. The bulk density (ρm) obtained for all the samples were much lower than the X-ray density (ρx). The absorption bands displayed by the spectra of FTIR correspond to the tetrahedral and octahedral sites which display signature of hexagonal structure for all the samples. Dielectric behavior was explained on the basis of conduction mechanism through hopping of electrons between Fe3+ and Fe2+ ions and Maxwell-Wagner model. Nyquist plots confirmed the grain boundary contribution in all the prepared Y-type nano hexaferrites samples exhibiting single semicircle. Q values obtained were high and observed above 2.5 GHz. The values of quality factor highlight the possibility of tailoring the operational frequency through compositional control. This suggested the utilization of these materials in Multi-layer chip inductors (MLCIs) at high frequency. The variation in magnetic parameters was discussed in terms of strength of exchange interactions and cations occupancy on different sites. Saturation magnetization and coercivity were found quite high for Dy-Co doped Sr-Ba-Zn hexaferrites and Gd-Co doped Sr-Ba-Cu hexaferrites which suggested the possible utilization of these materials in making permanent magnets. Sr-Ba-Cu based hexaferrites doped with Nd-Ni and Sr-Ba-Zn based hexaferrites doped with Pr-Ni indicated soft characteristics and proved to be suitable for utilizing the prepared hexaferrite materials in fabricating electromagnetic materials and sensors working at higher frequencies. The findings summarized here in current research are useful for exploring the significance of rare-earth transition metal co-doping on the transport properties of prepared Y-type nano-hexaferrites and provide a way for utilizing these hexaferrite materials in making permanent magnets and electromagnetic devices operating at higher frequencies.