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Abstract Using the flux method, we successfully synthesized Co-substituted Ca–La magnetoplumbite-type ferrite single crystals, Ca x La y Fe z Co w O 19 (Ca–La–Co system), a base material for high-performance hard ferrite magnets. Wavelength-dispersive X-ray analysis revealed that the chemical compositions of the obtained crystals depended on both the starting composition and reaction atmosphere. The fraction of Fe + Co to Ca + La deviates from the canonical value of 12, and the Co content, which is essential in magnetic anisotropy, improves with the synthesis under an oxygen gas stream. In addition, the magnetic anisotropy is enhanced by the Co substitution, as expected, but also depends on the Ca/La ratio, suggesting an appreciable effect of Fe 2 +. The magnetocrystalline anisotropy can be larger in the Ca–La–Co system than in the Sr–La–Co system. Graphical abstract Anisotropy field, H A , at 5 K for the Co-substituted Ca–La magnetoplumbite-type ferrite, Ca x La y Fe z Co w O 19 , plotted against Co content w. Literature data of the Sr–La–Co system are also plotted for comparison. fx1 Highlights • Successful synthesis of Co-substituted Ca-La magnetoplumbite-type ferrite single crystals. • Enhancement in the magnetic anisotropy by the Co substitution. • Magnetocrystalline anisotropy larger than the Sr-La-Co ferrites. [ABSTRACT FROM AUTHOR]

The cation compositions in the Ca–La magnetoplumbite-type (M-type) ferrite, Ca x La y Fe z O 19 , prepared from various initial fractions of reagents, were analyzed by wavelength-dispersive X-ray (WDX) spectroscopy. The reliability of the WDX composition analysis was confirmed by a crosscheck using inductively coupled plasma atomic emission spectrometry (ICP-AES). For particular polycrystalline samples furnace-cooled from 1250 ° C , the solubility ranges of Ca, La, and Fe were found to be 0.45 ≤ x ≤ 0.70 , 0.39 ≤ y ≤ 0.66 , and 11.82 ≤ z ≤ 11.92 , respectively, assuming x + y + z = 13 . Despite that the samples were synthesized from various starting compositions, the values of z / ( x + y ) of the matrix M phase are smaller than the M-type regular value, 12, for all the samples and comes in a very limited range at ∼ 11 , suggesting most probably Ca occupation at particular Fe sites or Fe deficiency due to insertion of stacking fault to Ca/La/O packing. Single crystals of Ca x La y Fe z O 19 with various x / y ratios were synthesized successfully by the self-flux method, followed by the characterization of their magnetic properties. The saturation magnetization and the Curie temperature were found to be almost independent of the cation composition. In contrast, the hard-axis magnetization process at low temperature depended significantly on the Ca/La ratio, and showed a sharp jump at ≲ 10 kOe, which can be attributed to a spin reorientation transition associated with the appearance of Fe 2 + . [ABSTRACT FROM AUTHOR]

The Na 2 O flux method was successfully applied in the single crystal synthesis of the magnetoplumbite-type strontium ferrite with La–Co co-substitution ( Sr 1 − x La x Fe 12 − y Co y O 19 ) , which is a familiar base material for commercial permanent magnets. The initial amount of Na 2 O flux was fixed in the molar ratio of Na/(Sr+La)=5.17. Composition analysis revealed discordance between La and Co concentrations ( x > y ) in the obtained crystals, indicating that the extra charge introduced by the Co 2 + substitution for Fe 3 + is not compensated by La 3 + for Sr 2 + . In the present growth condition, the necessary amount of La is nearly twice that of Co ( y / x ≃ 0.55 ) , suggesting valence instability of an appreciable amount of Fe 3 + to Fe 2 + . Single crystalline magnetization measurements showed that the substitution markedly enhances the magnetic anisotropy and slightly raises the saturation magnetization. Remaining problems, which should be resolved before the experimental determination of the Co site occupation, are also discussed. [ABSTRACT FROM AUTHOR]