[en] The magnetic properties of a series of fine particle iron oxides, oxyhydroxides and hydrated oxyhydroxides are discussed with reference to the data obtained from low-temperature, high-field Moessbauer spectroscopy experiments, using a two-sublattice atomic spin Hamiltonian model to help in the interpretation of the results. (orig.)

[en] Moessbauer spectra are obtained for a single crystal of α-FeOOH, with a magnetic field of up to 10T applied along the c axis. No spin reorientation is observed, indicating a lower limit of 6 x 10⁴ J/m³ for the anisotropy constant K. A theoretical estimate gives K > 1.1 x 10⁶ J/m³. (Auth.)

[en] The characteristics of the spin-flop transition in K₂FeF₅ and Rb₂FeF₅ are found by Moessbauer spectroscopy to be very different, and are discussed in relation to the ordered magnetic structures of the two systems. (Auth.)

[en] The static and dynamic magnetic behaviors of mechanically alloyed Fe₉Cu₅Ag₈₆ have been investigated by field-dependent DC magnetization and frequency-dependent AC susceptibility. The results reveal the coexistence of small Fe particles and ferromagnetic particles of larger size. Rietveld refinement of the X-ray diffraction patterns confirms the existence of nanometric Fe grains (∼6 nm) and of Ag (∼18 nm). Despite the low Fe content, the existence of interactions among the magnetic particles is evident, as deduced from Henkel plots

[en] Simultaneous reduction of aqueous solutions of CuSO₄ and MSO₄ (M=Fe, Co) by NaBH₄ has been carried out. If the pH is uncontrolled, the precipitation of Cu²⁺ is favoured. At fixed pH congruent with 7, the Cu amount depends on the initial solution. The precipitate is an heterogeneous alloy including a solid solution of FCC Fe-Cu. The effects of magnetic fine particle structure are shown by M(H) and AC susceptibility

[en] Granular alloys of Fe_xCu_xAg_100-2x (x=15, 35) have been produced by mechanical alloying. The x=15 alloy is composed of Fe(Cu) and Ag nanocrystals, whereas the Fe₃₅Cu₃₅Ag₃₀ is amorphous. DC magnetisation and AC susceptibility (5-300 K) show a maximum about 150 K for the x=15 alloy. The magnetisation has been fitted using log-normal distribution of grain sizes. The effect of interparticle interactions is discussed

[en] Spin-flop transitions in K₂FeF₅ subject to an applied field (i) parallel to the easy axis, and (ii) directed at 33⁰ to the easy axis are found to be (i) abrupt and (ii) smooth, in accordance with theoretical predictions. (orig.)

[en] Moessbauer spectra of three neutron-irradiated polycrystalline haematite (α-Fe₂O₃) samples have been recorded at 4.2 K in applied fields of up to 10 T. Field-induced phase transitions were observed, and were found to differ markedly from those that occur in non-irradiated haematite. In two lightly irradiated samples, transitions were detected from a state with Fe³⁺ spins near the [111] axis ('antiferromagnetic phase') to one where the spins are almost perpendicular to both the applied field and to the [111] axis ('weak ferromagnetic phase'). In the case of a heavily irradiated sample, in which the spins were initially in the weak ferromagnetic phase, the spins were observed to lie almost perpendicular to applied fields of greater than ∼ 4.5 T. The difference in behaviour in irradiated and non-irradiated haematite is attributed to a smaller difference in anisotropy energy, in the irradiated samples, between the antiferromagnetic and weak ferromagnetic phases at 4.2 K. (Author)

[en] Magnetic Moessbauer spectra have been observed at low temperature for samples of YBa₂(Cu_1-xFe_x)₃O_6.5+p with Fe levels x=0.01, 0.02, 0.04, 0.10 and 0.20. Fits to these complex magnetic spectra were constrained by simultaneous fitting of low temperature magnetic and high temperature nonmagnetic spectra of the same sample. The fits revealed two magnetic components, an Fe³⁺ magnetic sextet most prominent at x=0.20 and, for smaller values of x, a complex component whose fitting required a distribution of magnetic hyperfine fields. The temperature dependence of the hyperfine fields of this latter component gave values of T_hf where the magnetic hyperfine field appears. (orig.)

[en] The high-temperature superconductor with the nominal composition YBa₂Cu₃O_7-δ has been doped with iron 93% enriched in ⁵⁷Fe. When 1.5 at% Fe substitutes for Cu, the transition temperature is reduced by about 30 K with full ac shielding (χ'=-1/4π) achieved by ≅ 40 K. At room temperature the Moessbauer spectrum consists of three overlapping doublets. Below 10 K, hyperfine-field splitting is observed; relaxation still takes place at T=1.8 K. (orig.)