Hexagonal ferrites of X-, W-, and M-type in the system Sr-Fe-O: A comparative study

Three hexagonal ferrites from the Fe-rich part of the pseudo-binary system SrO-Fe203 were investigated. Besides the well-known M-type SrFe12O19 two other ferrites were found to exist at high temperatures: W-type SrFe22+Fe163+O27 and X-type Sr2Fe22+Fe283+O46 ferrites. A detailed characterization of the X-type Srferrite is reported here for the first time using XRD, HRTEM, magnetization measurements, Mbssbauer and Fe-57 NMR spectroscopies and ab initio calculations of the electronic structure. The results are compared to those of W- and M-type Sr ferrites. Mossbauer spectra were analyzed with six Fe contributions in the case of the X-type, seven Fe-sites for the W-type and five Fe sites for the M-type in agreement with crystal structure arrangements. Based on a detailed analysis of the NMR spectra in comparison with ab initio calculations the NMR lines were assigned to individual crystal sites. A preferential occupation of ferrous ions in the S blocks of the X- and W-type ferrites was elucidated from Mossbauer and NMR data as well as ab initio calculations. (C) 2015 Elsevier Inc. All rights reserved.