A temperature and magnetic field dependence Mössbauer study of ɛ-Fe2O3

ɛ-Fe2O3 was synthesized as nanoparticles by a pre-vacuum heat treatment of yttrium iron garnet (Y3Fe5O12) in a silica matrix at 300-C followed by sintering in air at 1,000-C for up to 10 h. It displays complex magnetic properties that are characterized by two transitions, one at 480 K from a paramagnet (P) to canted antiferromagnet (CAF1) and the second at ca. 120 K from the canted antiferromagnet (CAF1) to another canted antiferromagnet (CAF2). CAF2 has a smaller resultant magnetic moment (i.e. smaller canting angle) than CAF1. Analysis of the zero-field Mossbauer spectra at different temperatures shows an associated discontinuity of the hyperfine field around 120 K. In an applied field, the different magnetic sublattices were identified and the directions of their moments were assigned. The moments of the two sublattices are antiparallel and collinear at 160 K but are at right angle to each other at 4.2 K

Magnetic Structure of Hexagonal Ferrites Studied by Mössbauer Spectroscopy

Hexagonal Ba-ferrites of M-type (BaFe12O19) and W-type (BaMe2+2Fe3+16O27, Me -divalent cation) are promising materials for perpendicular magnetic recording. For this purpose it is desirable that their high uniaxial anisotropy be adjustable according to the specific requirements. Substitution of Co2+ for Fe2+/3+ cations usually decreases the magnitude of the uniaxial anisotropy and may be used to this end. In this work the influence of Co2+ content on the details of magnetic structure of Ba-hexaferrites is studied. Mössbauer spectra of 57Fe in single crystals of BaFe12-2xCo2+xTi4+xO19 and Ba(Fe2-xCox)2+Fe16O27 were measured at 293K. The dependence of the canting of magnetic moments on the concentration of Co was determined from the relative intensities of Mössbauer lines in the Zeeman nuclear multiplet and compared with the results deduced from the magnetic measurements

Formation of Hexagonal Ferrite Particles from the Disordered Fe2O3-BaO-B2-O3 System

It was shown that by high energy milling and subsequent annealing of the disordered powders from the BaO - Fe2O3 - B2O3 system crystalline particles of hexagonal barium ferrite are produced, whose formation commences slightly above 700 and is practically completed at about 800 °C. Both the X-ray diffraction and Mössbauer spectroscopy confirmed that the ensuing phase possesses the magnetoplumbite structure and its relative amount increases with the annealing temperature and/or time at the expense of the ferric oxide. These data are in reasonably good quantitative agreement with the results of the measurements of the magnetic moment of the particle systems

A temperature and magnetic field dependence Mossbauer study of (-Fe2O3)

International audience(-Fe2O3 was synthesized as nanoparticles by a pre-vacuum heat treatment of yttrium iron garnet (Y3Fe5O12) in a silica matrix at 300-C followed by sintering in air at 1,000-C for up to 10 h. It displays complex magnetic properties that are characterized by two transitions, one at 480 K from a paramagnet (P) to canted antiferromagnet (CAF1) and the second at ca. 120 K from the canted antiferro- magnet (CAF1) to another canted antiferromagnet (CAF2). CAF2 has a smaller resultant magnetic moment (i.e. smaller canting angle) than CAF1. Analysis of the zero-field Mossbauer spectra at different temperatures shows an associated discontinuity of the hyperfine field around 120 K. In an applied field, the differen

57^{57}Fe-enriched perovskites M(Fe0.5Nb0.5)O3(M–Pb,Ba)M(Fe_{0.5}Nb_{0.5})O_{3} (M – Pb, Ba) studied by Mössbauer spectroscopy, NMR and XRD in the wide temperature range 4.2–533 K

The 57Fe enriched almost single-phase perovskites Pb(Fe0.5Nb0.5)O3 (PFN) and Ba(Fe0.5Nb0.5)O3 (BFN), prepared by a ceramic method (solid-state synthesis), were studied by Mössbauer spectroscopy, nuclear magnetic resonance (NMR), conventional and synchrotron X-ray powder diffraction (XRD). The temperature dependences of hyperfine and structural parameters of PFN, BFN from 4.2 K to temperatures above ferroelectric ordering of PFN (TS ∼ 375 K), with attention to the values of magnetic and structural transitions, were obtained. The antiferromagnetic magnetic ordering transitions were found under the Néel temperatures TN ∼ 167(3) K and 32(2) K for PFN and BFN, respectively. The spin-glass transition was at TG ∼ 10(3) K and 20(5) K for PFN and BFN, respectively. In PFN sample a small change of structural parameters around TN and structural change from trigonal to cubic structure at T ∼ 400 K was observed by XRD. The temperature dependence of XRD shows stable cubic structure in the temperature range from 4.2 K to 530 K for BFN. From Mössbauer and NMR spectroscopies it is found that both structures have perturbed environments for Nb and Fe. However, in case of PFN the low values of transferred hyperfine fields disfavour random Fe/Nb arrangement and allow proposing a picture of Fe/Nb arrangement