[en] Moessbauer effect has turned into one of the most commonly used spectroscopies in condensed matter research. The sensibility of Moessbauer spectroscopy to detect the presence of metallic phases even in small percentages in alloys has converted it into a highly valuable tool for phase transformation research of different systems. The different perturbations produced by dopant atoms on ultra thin fields of iron atoms from different phases with different crystalline structures, or with different dopant atoms coordinations, has enabled the postulation of models for the transformation mechanisms between phases. Following very detailed works, at present it can be undertaken a research in this field with a great level of assignation reliability to each signal coming from the different phases existing in a certain alloy or steel sample. In this work, a brief description of the technique principles is presented, trying to emphasize the types of problems that can or cannot be solved by Moessbauer spectroscopy. Its potentialities and limitations through some applications are also discussed

[en] Moessbauer spectroscopy (MS) has played a significant role in the determination of magnetic orderings and anisotropy energies of antiferromagnetic materials. The capability of the technique to give a detailed description of the magnetic behavior and in some cases of the magnetic structure of the compounds under study is exemplified by recent investigations on linear antiferomagnets, L-type ferrimagnets and systems displaying antiferromagnetic orderings of lower dimensionalities. (author)

[en] Published in summary form only

[en] Procedures related to the preparation of samples for Moessbauer spectroscopy studies of phase transformations in metals research are discussed in examples of works undertaken by the authors; (i) determination of austempering kinetics of compacted graphite cast irons, (ii) CEMS studies aimed at finding suitable polishing treatments that reproduce the bulk phase proportions, (iii) CEMS investigations on samples polished by spark planing, and (iv) the research of surface processes produced by laser melting treatments. (orig.)

[en] Short communication

[en] Procedures related to the preparation of samples for Moessbauer spectroscopy studies of phase transformations in metals research are discussed in examples of works undertaken by the authors; (i) determination of austempering kinetics of compacted graphite cast irons, (ii) CEMS studies aimed at finding suitable polishing treatments that reproduce the bulk phase proportions, (iii) CEMS investigations on samples polished by spark planing, and (iv) the research of surface processes produced by laser melting treatments

[en] Moessbauer spectroscopy in zero applied field performed on powder samples of monoclinic FeNaP₂O₇ denote spontaneous magnetic ordering at temperatures below 29.2±0.2 K. Preliminar results from susceptibility and neutron diffraction measurements, currently in progress, establish the same P2₁/c space group as the crystalline structure and an equally sized magnetic cell for the array of spins. The hyperfine fields of the two antiferromagnetic sublattices obtained from Moessbauer spectra display coincident Brillouin-type temperature dependences with an extrapolated OK value of 55.0±0.3 T. Below the Neel temperature the spin orientation does not change relative to the crystalline axes. Mean field theory self-consistent calculations performed in order to estimate the relative magnitudes of the exchange interactions produced the values: J_AB=-0.61 cm^-1, and J_AA=-0.37 cm^-1. The antiferromagnetism of the system is likely to originate in the different relative numbers of superexchange pathways between sublattices. (orig.)

[en] A ball-milling treatment in air for 30 min is enough to reduce anhydrous bulk hematite (α-Fe₂O₃) grains to nanometric sizes. For milling times, t_m, of 15, 30 min, 1 and 2 h, the crystals suffer an anisotropic lattice dilation, which is more pronounced for the smaller average grain sizes attained. Moessbauer and susceptibility results show that the process alters the effective Morin temperatures, T_M. The transition occurs less sharply than for the non-milled material and spreads over a maximum extent of 50 K for t_m=30 min. The susceptibility data indicate that the T_M for the fraction of material undergoes the transition shifts toward values not lower than 235 K. For t_m=10 h the transition is suppressed down to 12 K. Our results do not allow distinguishing bulk from surface regions of the grains. In addition, the disorder brought about by the milling reduces the magnetic response in the weak ferromagnetic state of α-Fe₂O₃. The modification of T_M seems to depend mainly on the anisotropic dilation of the unit cell that affects the whole grain and it is related to the nanometric grain sizes achieved

[en] The effect of the particle size and ball-mill-induced defects on the magnetic properties of cupric oxide has been assessed by magnetic measurements. Nanoparticles with an average strain ε=0.035 and average crystallite size D=9 nm show a susceptibility one order of magnitude higher than the starting material. Up to room temperature, instead of the increasing susceptibility found in bulk samples, a Curie-Weiss-like behavior is observed above the ordering temperature of ca. 230 K

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