Magnetic and dielectric spectroscopic studies in Zn substituted Y-type barium hexaferrite

Highlights: • Zn substituted Co₂Y hexaferrites were prepared in single phase form. • Saturation magnetization increases with Zn substitution at Co site. • Spin reorientation transition and Neel temperatures decrease with Zn substitution. • Frequency independent permeability with low loss is observed. • The ac conductivity data follows the overlapping of large polaron tunneling model. Zinc substituted samples of Y-type barium hexaferrite with chemical formula Ba₂(Co_1-xZn_x)₂Fe₁₂O₂₂ (0 $\le$ x $\le$ 1) were synthesized by solid state reaction method to tune their magnetic properties and to understand their dielectric relaxation. The samples are found to be in single phase form with rhombohedral structure as per the analysis of X-ray diffraction patterns using Rietveld refinement technique. Magnetization measurements show that these samples exhibit ferrimagnetic and spin-reorientation transitions. The ferrimagnetic transition temperature (T_c) is found to decrease from 600 K for x = 0 to 380 K for x = 1.0 and the spin reorientation transition temperature (T_s) decreases from 225 K for x = 0 to around 60 K for x = 0.75. They are explained in terms of weakening of super-exchange interaction and the reduction of the planar magnetic anisotropy with increase in Zn concentration. The saturation magnetization value (M_s) measured at room temperature is found to increase from 5.85 μ_B/f.u. for x = 0 to 8.43 μ_B/f.u. for x = 0.5 and is explained in terms of preferential occupation of Zn²⁺ ions at spin down tetrahedral sites, 6C_iv and 6C_iv*. The complex permeability measurements in the frequency range of 100 MHz to 1 GHz suggest that Y-type barium hexaferrite is suitable for applications in radio frequency (RF) and antenna devices in the high frequency band. The relaxation dynamics of charge carriers is studied by measuring the frequency (100 Hz–1 MHz) dependence of dielectric constant and electrical conductivity at different temperatures.