Mossbauer investigation of Sr-Fe-O hexaferrites with La-Co addition

Abstract

M-type Sr 1 La Fe 12 Co O 19 ferrite powders with = 0 to 0.4 were investigated using Mössbauer spectrometry in the 77 K-550 K temperature range. The Mössbauer spectra were fitted by assuming that Co 2+ is present in both 4f 2 and 2a octahedral sites, and that some Fe 2+ is present in the 2a site. On increasing , the main changes concern the Mössbauer contributions of the 12k, 4f 2 and 2b sites. These changes are interpreted in relation with the Co 2+ -Fe 3+ substitution at the 4f 2 site, the Fe 3+ -Fe 2+ valence change at the 2a site and the La 3+ -Sr 2+ substitution. The temperature dependance of the hyperfine field at the Fe sites of the Sr 0 6 La 0 4 Fe 11 6 Co 0 4 O 19 compound is similar to that of the unsubstituted compound. However, the curvature of the temperature dependence of the hyperfine field at the 12k site slightly increases with . This reflects the increase of the curvature of the temperature dependence of the magnetization of the substituted compounds.

Recent improvement of hard ferrite permanent magnets based on La–Co substitution

“…4). The spectra were fitted assuming a distribution of Co 2+ in 4f 2 (mainly) and 2a octahedral sites, in agreement with previous investigations [6][7][8]. As Co 2+ was introduced in lower proportion than La 3+ , a small amount of Fe 2+ is assumed to be present in the 2a site, to keep the electroneutrality, in agreement with the valence change of Fe 3+ to Fe 2+ that occurs at the 2a site in the LaFe 12 O 19 compound [13].…”

“…In agreement with the magnetic measurements, the presence of these magnetic impurities can be partly responsible for both the decrease of the coercive field and the decrease of the rectangularity for x > 0.2. The cationic distribution of Co 2+ in Sr 1−x La x Fe 12−x Co x O 19 hexagonal ferrites was recently investigated by Möss-bauer spectrometry, Raman spectroscopy, and nuclear magnetic resonance [5][6][7][8][9][10]. It was shown that most of the Co 2+ is substituted for Fe 3+ in the octahedral 4f 2 and 2a sites, in agreement with the magnetization measurements.…”

“…The intrinsic magnetic properties (anisotropy field, saturation magnetization) being strongly dependent on the atomic magnetism, investigations on the sublattice occupation of Co 2+ in the M-hexagonal crystal were recently performed for the fundamental understanding of this beneficial effect [5][6][7][8][9][10]. M ferrites crystallize in a hexagonal structure with 64 ions per unit cell on 11 different symmetry sites (P6 3 /mmc space group).…”

Magnetic properties of chemical coprecipitated Sr0.8La0.2Fe11.8Co0.2O19 powders

“…Their magnetic properties are qualitatively interpreted based on micromagnetic models, but there is still some research interest [2][3][4][5][6][7], focused on the development of a cheaper manufacturing process that will not affect the enhanced magnetic properties of these materials.…”

Structural analysis of co-precipitated Sr1−xLaxFe12−xCoxO19 powders

“…ossbauer spectrometry and nuclear magnetic resonance in Sr 1Àx La x Fe 12Àx Co x O 19 ferrites prepared by a conventional ceramic process [3][4][5]. It was shown that Co 2þ ions substitutes for Fe 3þ in both 4f 2 and 2a sites.…”