Magnetism of the UFe xAl 12− x alloys

Abstract

Polycrystalline samples of the ternary intermetallic alloys UFe x Al 12− x with x in the range 〈3.6–5〉 were studied. The alloys crystallize in a ThMn 12-type structure, belonging to the space group I4/ mmm (no. 139). Studies of the powder samples by X-ray and neutron diffraction techniques confirmed the phase homogeneity of all these materials with an iron concentration, x, below 4. The samples with a higher iron content contain a small addition of extra phases. Monochromatic circularly polarised Mössbauer source (MCPMS) measurements, carried out at 12 K in an external magnetic field of 1 T, were interpreted in terms of magnetic domains in otherwise randomly oriented powders. Magnetic moments of iron are arranged in spin-canted magnetic structures. The canting angles ( α) were estimated. The neutron data obtained for the sample with x=4.4 indicate that the two transition temperatures, observed previously by means of the magnetisation measurements, originate in different temperatures of the ordering of iron and uranium sublattices. Our data indicate that the range of iron concentration within which two transition temperatures are observed starts with UFe 4Al 8 alloys. However, the mechanisms underlying these transitions are different for various compositions and require further investigations. It is shown that even in the case of the magnetic domains formation of the sample the MCPMS technique can bring very valuable results.