We have investigated the local electronic properties and the atomic order in the Al100-x-yCuxFey phases using 57Fe Mössbauer as well as 27Al and 65Cu nuclear magnetic resonance (NMR) spectroscopies. We have studied samples along the existence domains of the icosahedral quasicrystalline (i-) and the high-order approximant phases, given by two close-lying parallel lines in the concentration diagram. In addition, we have also studied a series of intermediate concentrations situated between these lines and retained in a metastable i-phase by quenching. It is found that the 57Fe Mössbauer centre shift (isomer shift) and quadrupole splitting are linearly correlated with each other over the range of compositions and structures for all samples, which reveals systematic changes in the orbital occupations on Fe atoms with composition. In addition, it is found that the 27Al NMR average electronic shift follows this correlation. The results are discussed in terms of the hybridization of iron d states with the p and induced d states of Al. We have studied also a low-order cubic approximant phase containing Si as well as several non-approximant crystalline phases.

We present room temperature 57Fe Mössbauer centre (isomer) shift and electric field gradient (EFG) results in the Al100-x-yCuxFey icosahedral-quasicrystalline (i-) and crystalline phases. We have investigated the local electronic properties and atomic order along the existence domains of the quasicrystalline and approximant phases given by two close-lying parallel lines in the concentration diagram: the I-line, where the quasicrystal is stable, and the A-line, where the rhombohedral approximant is stable, and other high-order approximants (orthorhombic and pentagonal) as well as the quasicrystal phase are metastable. We have also studied a series of intermediate concentrations situated between the I- and A-lines retained in the metastable i-phase by quenching. It is found that the centre shift and EFG are linearly correlated to each other over the range of compositions and structures for both the I- and A-lines as well as the intermediate samples. This correlation results from systematic changes in the orbital occupations on Fe atoms with composition.

A series of RFe12−xMx-type alloys were stabilised with M = Mo and x = 2.5 for R = Y, Nd, Dy and Er. Magnetisation, ac susceptibility measurements and μ+SR spectroscopy results are in good agreement with a systematic 57Fe Mössbauer spectroscopy analysis. The strength of all local iron magnetic moments (and the related hyperfine fields), as well as the long range magnetic ordering, have been found to be markedly affected by the substitution of iron by molybdenum in Fe(8i) sites. It was found that the temperature dependence of the order/disorder phenomenology is well described by local magnetic correlation.

A series of RFe(12-x)M(x)-type alloys were stabilised with M = Mo and x = 2.5 for R = Y, Nd, Dy and Er. Magnetisation, ac susceptibility measurements and mu (+)SR spectroscopy results are in good agreement with a systematic Fe-57 Mossbauer spectroscopy analysis. The strength of all local iron magnetic moments (and the related hyperfine fields), as well as the long range magnetic ordering, have been found to be markedly affected by the substitution of iron by molybdenum in Fe(8i) sites. It was found that the temperature dependence of the order/disorder phenomenology is well described by local magnetic correlation.

The icosahedral AlCuFe quasicrystal is stable at low temperature only along a narrow line-like concentration domain corresponding to a well defined substitution rule. Along a nearby domain, parallel to the first, the stable rhombohedral approximant and the metastable pentagonal and orthorombic approximants are found. We have investigated the local electronic properties and the local atomic order along these two domains using Fe-57 Mossbauer and Al-27 and Cu-65 NMR, spectroscopy. At a given composition no differences could be detected between icosahedral and approximant states showing that the local electronic and atomic structures are insensitive to the nature of the long range order. Within each domain the local properties are found nearly independent ai the composition. Much larger changes are observed when going from one domain to the other, although the composition variations involved can then be much smaller than within each domain. These results show the existence of a close relationship between the local electronic structure and the shape of the existence domains.

Mossbauer spectra of beta-rhombohedral boron with interstitially distributed iron atoms up to 3.33 at% are presented. Taking into account that the six D sites in the unit cell are saturated by two Fe atoms, the distribution of the Fe atoms on A and D sites proved to be simply statistical. At lower Fe contents single iron atoms on A sites are ionized to Fe3+, while towards higher Fe contents a rapidly increasing share of Fe2+ ions is found. On D sites the ionization of single Fe atoms is 2+, but it changes to 3+, when two Fe atoms are accommodated in the D sites of one unit cell. The isomer shift of the Mossbauer doublets yields an estimation of the electron transfer to the boron framework. Transition from p- to n-type takes place, when six electrons per unit cell are transferred from the iron ions to the boron framework. This number corresponds to the sum of the unoccupied sites in the upper valence band and the possible electron traps generated by an electron-phonon interaction in the B-12 icosahedra.

The antiferromagnet FeBr2 has been studied by Mossbauer spectroscopy in external fields both in the metamagnetic region below the multicritical temperature T-MCP and in the second-order transition region above. The local magnetization shows that the metamagnetic transition occurs by spin flips, as in simple models. However, in the second-order transition region, the local magnetization of the sublattice oriented antiparallel to the external field varies continuously but remains parallel to the c axis. This can only be understood if the external magnetic field induces strong transversal spin precession of the moments on the antiparallel sublattice. This shows that the anomalous maxima in the imaginary part chi '' recently found in the ac susceptibility [M.M. Pereira de Azevedo et nl., J. Magn. Magn. Mater. 140-144, 1557 (1995)] and denoted H- below the critical field H-C(T), and H-+ above, can be understood as being caused by noncritical transversal spin fluctuations.

We have investigated Fe2+xTi1−x alloys (−0.05 < x < 0.10) by 57Fe-Mössbauer spectroscopy (4.2–310 K). The spectra are well described on the basis of local magnetic effects associated with 6h and 2a sites. For T>200 K, stoichiometric Fe2Ti shows a complicated magnetic behavior.

The icosahedral quasicrystal Al100-x-yCuxFey is stable at low temperature only along a narrow line-like domain around Al62Cu25.5Fe12.5. In a nearby narrow line-like domain parallel to the first, the icosahedral structure transforms at low temperatures into a stable rhombohedral approximant (3/2) phase. For the first time, we have investigated the local electronic properties and local order along these stability lines, using both 57Fe Mossbauer and 27Al NMR spectroscopy. We show that the local properties (as given by the 57Fe central line shift and quadrupole splitting and 27Al average line shift and line shape) are insensitive to the nature of the long-range order, icosahedral quasicrystal or rhombohedral approximant, at a given composition. In addition, a new pentagonal approximant found along the rhombohedral line gave the same results as the quasicrystal for the same composition. The changes in the electronic properties along the two stability lines are about a factor of three smaller than the changes from the stable icosahedral to the stable rhombohedral domains although there is a factor of three larger change in concentration. These observations are consistent with the constant value of the number of electrons per atom (referred to as e/a) along the lines, and changes in e/a between them, as estimated from the alloy composition.

It is known that the structure and thermal stability of the AlCuFe icosahedral quasicrystalline (i-QC) phase is extremely sensitive to the exact composition. A stable, ideally quasiperiodic phase exists only along a line around Al62.0Cu25.5Fe12.5. The other i-QC samples show structural changes when annealed around 700 °C. The57Fe Mössbauer EFG properties and isomer shifts of these various i-QC phases and of the new rhombohedral approximant phase are presented, and compared with the properties of the Al site investigated by NMR. Certain new systematic trends will be presented.

Magneto-volume effects have been calculated and shown to exist in Fe2Ti alloys. Since Mössbauer spectroscopy provides insight into local magnetic properties we have performed such measurements in the temperature range 4.2 K