Flux growth of magnetoplumbite-type strontium ferrite single crystals with La–Co co-substitution

Abstract

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.

Co site preference and site-selective substitution in La–Co co-substituted magnetoplumbite-type strontium ferrites probed by 59Co nuclear magnetic resonance

“…The compositions of metallic elements, x and y, were determined by wavelength-dispersive x-ray spectroscopy (WDX). See [13] for details of the crystal growth and characterization. In synthesizing Sr-La-Co samples under ambient atmosphere, the Co content, y, is generally smaller than that of the La concentration, x.…”

“…See [14] for the details of the HIP-synthesized samples. For the samples treated in the present study, lattice parameters at room temperature and the anisotropy field, H A , at 5 K [13,14] are listed in table 1. The lattice parameters were estimated from powder x-ray diffraction data measured by X'Pert PRO Alpha-1 PANalytical with use of Cu-K α1 radiation.…”

“…For the Sr-La-Co system, although it was widely believed that Co mainly occupies the octahedrally coordinated 4f 2 site [8], it is now gradually accepted that Co mainly occupies the tetrahedrally coordinated 4f 1 site and partly octahedrally coordinated 2a and/or 12k sites [5,6,9,10]. Furthermore, it has been revealed that, in the samples synthesized under ambient atmosphere, La 3+ content, x, and Co 2+ content, y, are not necessarily identical but in general x>y, and their difference is compensated by the reduction of Fe 3+ to Fe 2+ [4,[11][12][13]. In order to get information on Co occupation sites, we have previously reported the result of 59 Co nuclear magnetic resonance (NMR) experiment for the Sr-La-Co sample synthesized under ambient atmosphere [7].…”

Magnetocrystalline anisotropy of La- and Co-substituted M -type strontium ferrites: Role of Co2+ and Fe<

“…To remove these extrinsic effects, it is required to study using single crystals, though there are only a few reports dealing with single crystal growth. [11][12][13] In this paper, we report crystal growth, compositional analysis, and magnetic properties of single crystals of Sr 1−x La x Fe 12−y Co y O 19 , and discuss the origin of the enhancement of magnetocrystalline anisotropy in this system. In our single crystals, content of La is greater than or equal to that of Co, indicating presence of Fe 2+ .…”

Single crystal synthesis and magnetic properties of Co2+-substituted and non-substituted magnetoplumbite-type Na–La ferrite

“…Single-crystal measurements are crucial in estimating the intrinsic MA of materials. However, such measurements have been limited for La-Co SrM [5,6] and La-Co CaM [4]. Here, we focus on Co 2+ -substituted M-type Na-La ferrite.…”