The structures of Sr 2 FeO 3 F, Sr 2 FeO 3 Cl and Sr 2 FeO 3 Br have been investigated using powder neutron diffraction (PND). All three ferrates crystallise in the primitive tetragonal space group P4/nmm and the anions are fully ordered giving iron oxygen square pyramids separated by rock salt type layers of strontium halide. 57 Fe Mo È ssbauer data have been collected and con®rm one iron(III) site of distorted octahedral geometry in all three structures. Variable temperature PND data have been used to determine the d2a62c magnetic superstructure of Sr 2 FeO 3 F.

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The crystal structure of the alloy Fe3Ga has four inequivalent crystallographic iron sites. Mössbauer spectra recorded at 4.2 K were able to be fitted with four sextets corresponding to these sites. Measurement of the hyperfine fields Bhf gave values 271 kG, 191 kG, 152 kG and 195 kG respectively. For the series (Fe1-xTix)3Ga4 spectra were recorded at 4.2 and 300 K for x = 0.05, x = 0.10 and x = 0.15. These spectra were fitted to five sextets, each associated with a distinct iron site. The magnetic ordering temperature TC was observed to be essentially unchanged for 0 x0.15. Site preference for Ti atoms was observed for x = 0.10 and x = 0.15 causing a large change in hyperfine field values at a neighbouring site. Similar Mössbauer studies were made on the series (Fe1-yCry)3Ga4 (0 y0.20). Spectra at 4.2 K could be fitted with four sextets but continuous reductions in hyperfine field values and ordering temperature TC were observed with increasing y. The contrast in the magnetic behaviour of the two series is associated with different patterns of substitutional site preference.

The crystal structure of the parent alloy of the series under investigation has four distinct iron sites. Mössbauer spectra of the series with recorded at 293 and 4.2 K and fitted with four components show little site preference for Mn substitution up to x = 0.15. At x = 0.20 evidence for site preference is observed. The magnetic phases at 4.2 K were deduced from changes in the Mössbauer spectra in applied fields. The alloy with x = 0.20 is found to be ferromagnetic. Alloys with x = 0.05, 0.10 and 0.15 show evidence of a canted spin phase. A transition from a canted to a ferromagnetic phase is observed at applied fields T for the x = 0.15 alloy. Phase diagrams constructed from Mössbauer and magnetization results are compared with the predictions of a generalized theoretical model which incorporates ferromagnetic and antiferromagnetic interactions.

Multilayer samples of Ni/Fe and Fe/Cu/NiFe, fabricated by sputtering and characterized by transmission electron microscopy and electron diffraction, were studied by 57 Fe Mössbauer spectra and magnetization measurements. Mössbauer spectra taken in zero applied field at 300 K and 4.2 K showed midlayer and interface iron sites in Ni(20 Å)/Fe(x Å) samples with x = 20 Å, 30 Å, 50 Å, 80 Å and in-plane spin orientation. The reorientation of the magnetic moments at 4.2 K in increasing fields applied normal to the layers when combined with magnetization measurements enabled the magnetic anisotropy energy K of each sample to be evaluated. The trend of the values of K with iron layer thickness gave volume and interface anisotropy components K V = (−5 ± 1) × 10 4 J m −3 and K S = (−0.6 ± 0.4) × 10 −3 J m −2 where negative values indicate in-plane preference. Similar measurements on a series of samples of Fe(30 Å)/Cu(x Å)/Ni(80%)Fe(20%)(30 Å) with x = 10 Å, 20 Å, 30 Å, 50 Å showed a tendency toward increasing in-plane anisotropy energy K with decreasing thickness of the non-magnetic Cu layer.