R. B. Scorzelli

57Fe and119Sn Mössbauer studies on La1.25Nd0.6Sr0.15CuO4

Abstract57Fe- and119Sn Mössbauer effect studies on 0.5 at %57Fe (or119Sn) dopednon-superconducting La1.25Nd0.6Sr0.15CuO4 in the temperature region 300 K ≧T≧4.2 K reveal an onset of local magnetic ordering occurring atTm≅32 K for both57Fe—as well as119Sn-doped samples. The local magnetic ordering shows up in the presence of a very large transferred hyperfine field ofBthf≅11.0(5)T at the119Sn nuclei. Since such a large field is neither present in antiferromagnetic La2CuO4, nor in superconducting La1.85Sr0.15CuO4 or overdoped La2−xSrxCuO4 (x=0.4), the occurrence of such local spin correlations seems to be a signature of the non-superconducting low temperature tetragonal phase of La1.25Nd0.6Sr0.15CuO4.

Magnetic ordering of YBa2(Cu1−xFe x )3O7

The Mössbauer spectra of YBa2(Cu1−xFex)3O7 at room temperature show several doublets attributed to Fe in Cu(1) sites with different oxygen configurations. Here we present a systematic study performed at 4.2 K forx=0.005, 0.01, 0.03, 0.05, 0.10, 0.15. To obtain information about the magnetic ordered state two samples, withx=0.005 andx=0.15, have been studied at 4.2 K underBext=5 T. The Mössbauer spectra indicate that the iron moments are polarized forx=0.005, while in the ordered state (x=0.15) they have an antiferromagnetic or spin-glass-like arrangement with high anisotropy.

VERY THIN FE/NI MODULATION MULTILAYER FILMS UNDER ION BOMBARDMENT

We investigated the effect of noble gas irradiation (He, Ne, and Xe) on Fe–Ni multilayers with a very thin modulation and nominal composition in the Invar region Fe0.63Ni0.37. The evaluation of the formation/stability of the Fe–Ni phases formed under irradiation with different ions and doses was followed by conversion electron Mossbauer spectroscopy. The magnetic hysteresis curves were also obtained in order to correlate the hyperfine pattern with magnetic properties. The as-deposited sample reveals mainly the characteristic α-Fe while He- and Ne-irradiated samples clearly show a phase transformation with segregation of γ-FeNi phases with different Ni concentrations, a magnetic atomically ordered phase (∼50% Ni), and a nonmagnetic phase (⩽30% Ni). However, mixing with Ne is more effective than with He for similar doses. The results obtained with Xe showed a large distribution of hyperfine fields similarly to previous results reported for Kr [C. Tosello, F. Ferrari, R. Brand, W. Keune, G. Marest, M. A. El ...

Mössbauer Spectrum and Debye-Scherrer Pattern of the Ordered Phase Fe-Ni (Superstructure Llo)

The Fe-Ni ordered alloy with superstructure Llo was extracted from the metal particles of LL-chondrite St. Severin and characterized by Mossbauer spectroscopy to be a single phase. Five superlattice lines corresponding to the Llo superstructure were identified in the x-ray powder diagram.

57Fe Mössbauer studies on semiconducting and superconducting La-Ba-Cu-O

Abstract La 2− x Ba x CuO 4 samples substituted with 57 Fe (less than 1%) were studied for 0≦ x ≦0.35. Despite the fact that there is only one Cu site which can be occupied by the iron-substituent, the 57 Fe Mossbauer spectra at room temperature show three quadrupole doublets whose intensities were followed in different steps of sample preparation. They are characteristic of Fe 3+ , and their Mossbauer parameters depend on the Ba content. One of the iron species may be due to defects since it disappears with further heat treatment, while the others are present even in the undoped La 2 CuO 4 . Magnetic ordering has been found at 4.2 K for samples with 0.5% Fe even in the superconducting samples with x =0.15.

Magnetic phase present in YBa2(Cu1−xFe x )3O6+δ oxides

The Mössbauer study of57Fe: YBa2Cu3O6+δ oxides was very important to establish the preferential occupation of Cu(1) site by Fe at very low concentrations. Recent determination of antiferromagnetic ordering for Cu moments in Cu(2) sites (T≈450 K) and our early observation of a small proportion of a magnetic phase at room temperature for Fe:YBa2Cu3O6 lead us to perform systematic studies of YBa2(Cu1−xFex)3O6 withx=0.005, 0.03, 0.05, 0.10 and 0.15 in order to obtain information about the iron occupation of Cu(2) sites.

On the mechanism of oxygen desorption in Fe:YBaCuO Superconducting oxides

Abstract “In situ”57Fe Mossbauer Spectroscopy experiments have been performed on Fe:YBaCuO samples, in vacuum at high temperatures. From the results obtained it has been possible to make evident the kinetics of oxygen loss in doped samples.

Phase stability in iron-nickel Invar alloys

The influence of the Invar anomalies upon the stability of FCC Fe-Ni is examined. Consideration of the coherence-strain energy indicates that spinodal decomposition is favoured by the Invar anomalies.

Mössbauer study on phase separation in FeNi multilayers under ion bombardment

Abstract We investigated the effect of noble gas irradiation (He, Ne, Ar and Xe) on FeNi multilayers with a very thin modulation and nominal composition in the invar region Fe 0.63 Ni 0.37 . The evaluation of the formation/stability of the FeNi phases formed under irradiation with different ions and doses was followed by conversion electron Mossbauer spectroscopy.

Iron-nickel superstructure in metal particles of Alfianello meteorite

We report on Mössbauer spectroscopy in metal particles of the Alfianello meteorite. The FeNi 50-50 ordered phase (tetrataenite) was detected in coexistence with a high proportion of the corresponding disordered phase. The order-disorder process is discussed in terms of shock events.