Cation distribution analysis of Sr-La-Co M-type ferrites by neutron diffraction, extended X-ray absorption fine structure and X-ray magnetic circular dichroism

Abstract

The occupation sites of lanthanum and cobalt ions in the LaCo substituted M type ferrite Sr 1¹x La x Co x Fe 11.6¹x O 19 , where x = 0.20 to 0.35, were analyzed by the neutron diffraction, the extended X-ray absorption fine structure (EXAFS) and the X-ray magnetic circular dichroism (XMCD) in order to understand the relationship between the local structure and the improvements of magnetic characteristics in the LaCo substituted M-type ferrite. The results of EXAFS analysis suggest that Co is partitioned in the 4f 1 , 2a and 12k sites, which is in a good agreement with the results of the neutron diffraction analysis. XMCD measurements also indicate that the ferric ions at the tetrahedral site 4f 1 is replaced by elements of a smaller magnetic moment.

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

“…Recently, Kobayashi et al [5] claimed that Co occupies 4f 1 , 2a, and 12k sites from the results of x-ray absorption spectroscopy (XAS) combined with neutron diffraction Rietveld refinement analysis. In addition, they claimed from the results of hard x-ray magnetic circular dichroism (MCD) experiment that Co occupies the tetrahedrally coordinated, namely 4f 1 , site.…”

“…The improvement of the magnetic performance by the Co substitution is mainly ascribed to the increase in the coercivity, namely the enhancement in the uniaxial anisotropy associated with the unquenched orbital magnetic moment of Co 2+ occupying at particular Fe sites. In both Sr-La-Co and Ca-La-Co systems, Co tends to occupy more than two Fe sites [4][5][6][7]. It is likely, however, that Co at particular sites only contributes to the uniaxial anisotropy, while the other Co is useless or even harmful in enhancing magnetic performance.…”

“…In order to improve magnetic performance with limited Co content, site-selective Co substitution is highly required; commercially it is important to reduce the usage of Co because of its unstable price and supply. 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].…”

Mössbauer effect of Ni-doped strontium ferrite

“…This has been supported by Raman spectroscopy [4]. However, this argument was found to be in discordance with the conclusion obtained recently from simultaneous analyses of neutron diffraction and extended X-ray absorption fine structure (EXAFS) spectra, which excludes 4 f 2 and 2b sites as possible Co occupation sites [5]. Furthermore, in previous studies, Co occupation at the 4 f 1 site has actually been suggested from neutron diffraction [6] and NMR measurements [3].…”

“…Furthermore, in previous studies, Co occupation at the 4 f 1 site has actually been suggested from neutron diffraction [6] and NMR measurements [3]. X-ray magnetic circular dichroism (XMCD) measurements also indicated that Fe atoms at the 4 f 1 site are replaced by Co [5]. This discrepancy may originate in the site assignment in Mössbauer analyses, for example, incorrect assignment between 4 f 1 and 4 f 2 sites with the same atomic fraction.…”