T. Kemény

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.

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.

STRUCTURE AND DYNAMICS OF CRYSTALLINE C60·n-PENTANE CLATHRATE

Clathrate type single crystals with the composition of C60(n-C5H12)0.88(C7H8)0.05 were grown from C60-toluene-petroleum ether solution. The structure of the crystals, determined by X-ray diffraction is b-face centered orthorhombic. A phase transition is observed at 190 K by differential scanning calorimetry.

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.

Laser melted FeB alloys

Abstract The structure of amorphous Fe100−xBx (17≤ × ≤ 50 at.%) alloys prepared by vacuum evaporating and by ns pulse laser melting of the same evporated layers has been compared using room temperature Conversion Electron Mossbauer Spectroscopy (CEMS). The width of the hyperfine field distribution (HFD) characteristic to the laser melted surface layer is 10% lower than that of the as received sample, being practically equal to the value observed for melt spun ribbons. A similar value was also found for the amorphous surface layer obtained by the laser melting of an Fe83B17 ingot consisting α-Fe and Fe2B crystals. It is established that a complete chemical mixing takes place during the life-time of the melt. The difference between the width of the HFD of evaporated and melt quenced alloys is attributed to an enhanced disorder in the evaporated sample.