I. Vincze

Magnetic properties of amorphous transition metal alloys

Abstract The chemical short-range order of metallic glasses will be discussed and it will be shown that the structural disorder has minor effects on the shape of the magnetization curve, on the magnetic moments and Curie temperatures.

Nucleation controlled transformation in ball milled FeB

Abstract X-ray diffraction reveals the loss of sharp crystalline peaks, and differential scanning calorimetry shows nucleation controlled transformation besides grain growth in mechanically ground FeB intermetallic compound. On the other hand, the Mossbauer hyperfine parameters are close to the values of the disordered intermetallic compound (α-FeB) and different from those of the amorphous FeB produced by sputtering or evaporation. This controversy is attributed to the disordered interfacial phase existing at the grain boundaries.

MOSSBAUER ISOMER-SHIFTS AND QUADRUPOLE SPLITTINGS IN THE AMORPHOUS IRON-BORON SYSTEM

Abstract The isomer shifts and quadrupoole splittings of amorphous Fe x B 1−x alloys (10 a/o ⪅ × ⪅ 90 a/o) were studied by 57 Fe Mossbauer spectroscopy. The isomer shift vs. composition can be described by the ▵φ ∗− and ▵n WS -terms of Miedemas cellular model to predict the heat of formation of binary alloys and an additional volume mismatch term. This term is necessary for boron-rich alloys ( x ⪅ 50 a/o). We conclude that these samples have a strained atomic structure. The values of the quadrupole splittings at the boron-rich side increase strongly, indicating that the Fe-atoms are squeezed into asymmetric atomic surroundings. Implanted iron into crystalline boron has a comparable isomer shift and quadrupole splitting as the boron-rich alloys.

Crystallization and local order of bulk AsxTe1−x glasses

Abstract The crystallization and the local order of the bulk AsxTe1−x (0.2 ⩽ × ⩽ 0.8) glasses have been investigated by DSC, X-ray and Mossbauer methods. During the crystallization a metastable phase has been observed between 0.35 ⩽ × ⩽ 0.5 and it was identified as fcc AsTe. The local surrounding of these AsxTe1−x glasses characterized by the 125Te Mossbauer measurements were compared with those of the stable monoclinic As2Te3, hexagonal Te and metastable fcc AsTe.

MAGNETIC-MOMENTS IN MANGANESE CONTAINING INTERMETALLIC COMPOUNDS

Magnetisation, diffuse neutron scattering, 57Fe Mossbauer measurements and nuclear magnetic resonance (NMR) studies were performed on the pseudobinary (Fe1-xMnx)2Y and (Fe1-xMnx)2B intermetallic compounds. It is shown that in both systems the Mn atoms possess magnetic moments and that all these magnetic moments are ferromagnetically coupled. The concentration dependence of the individual Fe and Mn moments has been derived from a combination of magnetisation, neutron and Mossbauer data. The mean Fe moments show a strong decrease with increasing Mn content; the Mn moments appear to be less concentration dependent.

Magnetic disorder in amorphous Fe-rich FeZr alloys

Abstract In the framework of a detailed investigation of the temperature, composition and magnetic field dependence of the magnetic properties of Fe-rich alloys, systematic composition dependence of the low temperature hyperfine parameters is reported. The existence of two different Fe local environments is confirmed and they are identified with the exclusively Fe coordinated compressed and with the partially Zr coordinated Fe atoms of average volume, respectively.

Investigation of the thermal relaxation in glassy Ni80−xFexP20 alloys

Abstract Electrical resistivity, dynamical Youngs modulus, internal friction, calorimetry, Mossbauer spectroscopy and electron microscopy studies of melt quenched Ni 80− x Fe x P 20 (x=0,1,3,5,10 and 20) amorphous alloys are reported. A significant composition dependence of the thermal relaxation is observed which is explained by substantial changes in the electronic structure on alloying.

Local structure of amorphous (Ni,Fe

Abstract The structure of melt quenched amorphous ( Ni , Fe)-Zr alloys is studied by 57 Fe Mossbauer spectroscopy. The composition dependence of the hyperfine parameters clearly indicates that beyond the qualitatively equivalent Fe sites observed at low Zr content, the fraction of a new inequivalent Fe site increases gradually with increasing Zr concentration. The crystallization product at 50 at% Zr is found to be a disordered metastable compound with the NiZr structure. The local environments of the amorphous alloys are described in a wide composition range by the preferential substitution of this structure.

CEMS investigation of near surface structure

Conversion Electron Mössbauer Spectroscopy (CEMS) studies are reported for as-cut and laser melted surfaces of single phase crystalline Fe2Y, Fe23Y6, Fe2Zr, Fe2B and FeB ingots. Disorder and the appearance of a new phase with a low value of the room temperature hyperfine field was observed for the Fe−Y and Fe2Zr ingots even on the as-cut surfaces due to the mechanical processing. In case of these ingots surface melting by ns laser pulses resulted in the formation of amorphous alloys. In case of the Fe−B ingots the formation of amorphous phase by laser melting was observed for Fe2B only, while in case of FeB the low temperature α-FeB modification appeared both, for mechanical processing and laser melting.

CEMS investigation of laser melted Fe−Zr alloys

Conversion Electron Mössbauer Spectroscopy (CEMS) studies are reported for as-cut and laser melted surfaces of Fe−Zr ingots in the 25–80 at.% Zr composition range. Disorder and amorphization was observed even on the as-cut surfaces due to the mechanical processing. Besides a significant enhancement of the non-crystalline fraction, surface melting by as laser pulses also results in the appearance of new metastable phases. Solidification via an extremely high cooling rate thus produces amorphous phase in composition ranges where its formation was previously assumed to be restricted to non melt-quenching methods only.