ИСТИНА

Here, we report on the single-domain nanoceramic of Al-doped strontium hexaferrite that displays unusually high room temperature values of coercivity, up to 40 kOe, and of natural (zero-field) ferromagnetic resonance (NFMR) frequency, up to 400 GHz. Single-domain Sr1-x/12Cax/12Fe12-xAlxO19(x = 4–6) particles are synthesized by a simple citrate auto-combustion method. The room temperature coercivity of the materials increases with aluminum content from 21.3 kOe (x = 4) to a maximum of 36 kOe (x = 5.5), the value that is the highest among ferrite materials to date. Moreover, the magnetic alignment of the particles leads to further coercivity improvement, up to 40 kOe. Due to large magnetic anisotropy the samples demonstrate NFMR with unusually high frequency – in the subterahertz band. The corresponding absorption lines shift with aluminum substitution from 160 GHz (x = 4) to 250 GHz (x = 5.5) [1]. Variation of annealing temperature and of chemical composition results in further increase of the NFMR frequency, up to 400 GHz at room temperature. We have also studied the effect of synthesis time on the particle morphology and magnetic properties of the materials. The procedure allows one to obtain SrFe8Al4O19 particles with mean diameters of 100–460 nm and coercivity that ranges from 14.5 to 18.4 kOe, while NFMR frequencies vary from 149 to 164 GHz, respectively. The obtained results contribute to the development of new low-cost materials with ultra-high coercivity and NFMR frequencies. Acknowledgements: This work was supported by RFBR, grant 20-02-00887. [1] E.A.Gorbachev, et al. Materials Today, 2020, V. 32, pp. 13-18