The crystal structure of β‐US2 was refined using single crystal X‐ray diffraction data. The lattice constants at room temperature are: a = 8.4803 Å, b = 7.1139 Å, and c = 4.1205 Å. The uranium atom is coordinated by nine sulphur atoms: two at a distance of 2.713 Å, two at 2.896 Å, two at 3.141 Å, one at 2.747 Å, one at 2.826 Å, and one at 2.888 Å. The magnetic measurements were carried out in the temperature range 4.2 to 1000 °K. The increase of the effective magnetic moment from 3.08 to 3.28 BM with temperature is explained on the assumption that the ground state is composed of four closely spaced singlets. The semiconducting character in the temperature range 4.2 to 650 °K was established with a forbidden gap ΔE≈1.2 eV.

The powder samples of (x = 4, 5 and 6) alloys have been measured by means of magnetization, Mössbauer effect, x-ray and neutron diffraction techniques in the temperature range 1.5 - 400 K. Both neutron and x-ray diffraction experiments showed that the positions f in all samples are occupied by iron, while the iron atoms in the samples with x = 5 and 6 locate also at j sites. A little f - j disorder exists in . The paper shows a change of the magnetic structure with an increase of iron content. The magnetic moments lie in a basal a - b plane. Iron atoms in alloy order antiferromagnetically. and alloys exhibit in general a ferromagnetic behaviour. However a detailed distribution of magnetic moments among different sites could not be determined unambiguously from the neutron data only. Nevertheless, combining information from neutron and Mössbauer experiments, one can infer that the ordering among iron atoms must be non-collinear. A magnetic ordering among uranium atoms has been found in only. Low-temperature thermal expansion varies nonlinearly with temperature and in all samples is negligible at low temperatures.

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ScFe 4 Al 8 and YFe 4 Al 8 crystallise in the tetragonal structure of the ThMn 12 -type. Whilst there exists antiferromagnetic ordering in the Fe sublattice below about 100-200 K in these compounds, they can be considered the reference materials for the RFe 4 Al 8 where R = magnetic lanthanide, U or Np. Our recent magnetic measurements in a low magnetic field of 50 Oe have revealed another pronounced anomaly in the temperature dependence of magnetic susceptibility at lower temperature (LT) than the Néel point. There is a clear difference in the temperature dependence of the magnetic susceptibility measured in zero field cooled (ZFC) and field cooled mode (FC). Thus a deviation from stoichiometry, spin-reorientation transition (SRT) and spin-glass (SG) state are discussed as possible reasons for the LT anomalies. The magnetic susceptibility of unoriented single crystals of ScFe 4 Al 8 and YFe 4 Al 8 does not follow either the Curie-Weiss or the modified Curie-Weiss law. At T ≈ 6 K both single crystals are partially transferred to the superconducting state.