ИСТИНА

M-type hexaferrites (M2+Fe12O19, M2+ = Pb2+, Ba2+, Sr2+) are well-known hard-magnetic oxide materials, which possess appropriate magnetic properties, good chemical and thermal stability, and low cost. Due to these factors, they are most producing magnetic materials by tonnage. However, since their magnetic properties are far from those of rare-earth magnets, the hexaferrites are under intensive investigations now. To achieve maximum magnetic properties, for example, the magnetic coercive force the hexaferrites must be at so-called single-domain state. A partial substitution of iron can lead to a considerable improvement of the magnetic characteristics, such as, to an increase in the saturation magnetization, the coercivity and the natural ferromagnetic resonance frequency (NFMR). Herein, we have manifested a facile method to produce single-domain strontium hexaferrite particles doped by ions such as diamagnetic Al3+, Ga3+ and paramagnetic Ru3+, Cr3+ ones. The samples were obtained by an optimized citrate-nitrate approach, that can be integrated into modern ferrite technology. The influence of each dopant on the saturation magnetization, the coercivity and crystal structure has been studied. It was shown that Al3+, Ga3+, Cr3+ doping leads to a considerable decrease in the saturation magnetization due to lower magnetic moment of the ions and their introduction into up-spin 12k and 2a iron sites. The exiting moment is that simultaneously with decline of the saturation magnetization the growth of the coercivity has been observed. For Al3+ doping record-high coercivity of 36 kOe was found for Sr0.54Ca0.46Fe6.5Al5.5O19 compound. Doping by Cr3+-ions leads to modest coercivity growth but still 14 kOe for SrFe7Al5O19 has been achieved. Introduction of Ga3+ ions up to x = 4 into the hexaferrite structure leads to a growth of coercivity up to 6.4 kOe; further increase in gallium concentration led to a decrease in the coercivity, while the saturation magnetization decreased with x during an increase of doping level. Ga3+ ions predominantly occupied 2a, 4f1, 12k and 2b sites, for example, for x = 6 gallium occupation factors were equal to 70, 64, 52 and 43 % for the mentioned sites, respectively, that led to a decrease in the magnetic anisotropy and to a modest decrease in the saturation magnetization. Doping by Ru3+-ions leads to a dramatical decrease in the coercivity and already at x = 0.3 the sample possesses soft-magnetic behavior. The work was supported by RSF grant no 20-73-10129.