Magnetic and Mossbauer Effect Study of Ca-Sc Co-doped M-Type Strontium Hexaferrite

The present study investigates the influence of Ca2+-Sc3+ co-dpoing on the magnetic properties of Sr1-x/12Cax/12Fe12-xScxO19 (x = 0.0 to 2.0) hexaferrites. The samples were prepared via a facile autocombustion technique followed by sintering in ambient air. X-ray powder diffraction patterns show the formation of the pure phase of M-type hexaferrite. The lattice parameters a and c increased with the Ca2+-Sc3+ doping. The compounds' magnetic properties were assessed as a function of temperature (10-300 K) and field (up to 6T). A rapid decline in room temperature coercivity from 5458 to 373 Oe and remanence value from 37 to 13 emu/g and a moderate decline in saturation magnetization from 76.9 to 57 emu/g were observed with increasing doping content from x = 0.0 to 2.0. The phase transition temperature, corresponding to ferrimagnetic to conical, was observed below 100 K, which disappeared at low doping content. The temperature-dependent behavior of magnetization and coercivity is discussed in view of spin non-collinearity due to the change in magnetic anisotropy. The Curie temperature dropped from 769 K at x = 0 to 568 K at the maximum substitution of x=2.0. The room temperature Mossbauer spectral analysis confirmed the preferred occupancy of Sc3+ at the 4f2 site and the influence of Ca2+ on the isomer shift values of the 2b site. The increased quadrupole shift values with the substitution implied distortion in 2b bipyramidal symmetry. The observed changes in magnetic properties and hyperfine parameters are ultimately tied to the preferred occupancy of Sc3+ at the spin-down 4f2 site.