Exploration of structural, Mössbauer, and hysteresis performance metrics of SrCoxZnxFe12−2xO19 hexaferrite for recording applications

Abstract

The present study aims to improve the magnetic properties with tunable coercivity of SrM hexaferrite by substituted Co and Zn ions instead of Fe and to elucidate in detail the changes in their structural, morphological, and site occupancy characteristics. Sr\({\text{Co}}_x {\text{Zn}}_x {\text{Fe}}_{12 - 2x} {\text{O}}_{19}\) (Co, Zn; x = 0.4, 0.8, 1.2, 1.6 and 2.0) powders were synthesized by the autocombustion sol–gel method. Substitution of Co–Zn ions caused the formation of magnetoplumbite and a secondary phase (CoFe₂O₄) in the structure. Increasing the Co–Zn content ratio led to a nonlinear increment in crystallite size ranging from 41.9 to 49.8 nm. SEM micrographs depicted platelet-shaped hexagonal particles that were nano-scale in thickness and micro-scale in diameter. Mössbauer spectra revealed that the substituent tends to occupy both spin-up sites 12k-2a-2b and spin-down sites 4f₁ and 4f₂ of crystal lattice from x = 0.4 to x = 2.0, which elucidate meagre change observed in magnetization, as per literature. The saturation magnetization (M_s) and remanent magnetization (M_r) were higher than the initial values of M_s = 75.26 emu/g and M_r = 26.95 emu/g. The highest coercivity and saturation magnetization was observed as, 4159 Oe and 80 emu/g, respectively, for x = 2.0. The squareness ratio (M_r/M_s) of x = 1.6 and x = 2.0 samples, was observed to be greater than 0.5, elucidating the existence of single-domain particles. The magnetic parameters M_s with tunable H_c, M_r/M_s, and magnetic susceptibility (dM/dH) results make the synthesized sample considerable for recording applications.