Crystal and magnetic structure of hexagonal anisotropic polycrystalline ferrites SrFe₁₂O₁₉ obtained by radiation-thermal sintering

Hexagonal anisotropic strontium ferrite has found wide application in the fabrication of permanent magnets, active media of UHF electronic devices, and photonics. The performance of hexagonal strontium ferrites depends largely on the synthesis technology. Anisotropic SrFe₁₂O₁₉ samples have been for the first time synthesized using radiation-thermal sintering (RTS) in a fast electron beam from an electron accelerator. The RTS temperature was varied between 1200 and 1400 °C, and the process time, from 10 to 90 min. The phase composition and lattice parameters of the samples have been monitored using X-ray diffraction and Mössbauer spectroscopy. The X-ray spectra have been recorded with a DRON-8 diffractometer in CoK_α1 radiation, and the Mössbauer spectra, using an MS1104E spectrometer with a constant acceleration at room temperature, the radiation source being Со⁵⁷ in a chromium matrix. The density of the specimens has been studied in accordance with Archimedes’ law on a UW620H electronic balance with a density measurement attachment. The X-ray diffraction and Mössbauer spectroscopy data show that the samples are single-phase and have the P6₃/mmc (No. 194) space group, corresponding to the hexagonal ferrite structure. The unit cell parameters a and c and the volume V of the samples have been studied as a function of RTS temperature for the sintering time t = 30 and 60 min. Also, the unit cell parameters a and c and the volume V of the samples have been studied as a function of sintering time for the RTS temperature T = 1300 °C. The lattice parameters a and c of the samples exhibit opposite dependences, suggesting anisotropic lattice distortion. The maximum magnetic texture degree achieved using RTS in anisotropic SrFe₁₂O₁₉ proves to be about 92%. It has been concluded on the basis of the Mössbauer spectroscopy data that the optimum magnetization degree of the SrFe₁₂O₁₉ samples is achieved for the following RTS modes (RTS temperature, °C / RTS time, min): 1300/60 and 1350/40. We show that the sintering temperature plays a considerably greater role in the RTS technology than the sintering time. Conclusion has been made that RTS can be used as an alternative technology of synthesizing polycrystalline anisotropic hexagonal SrFe₁₂O₁₉ ferrite. As compared to the conventional ceramic technology, RTS proves to be highly energy-efficient and cheap.