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.

The results of experimental investigations of the temperature dependences of the surface resistance and specific heat of ternary rare-earth compounds are presented: LuFe4Al8, ScFe4Al8, CeFe4Al8, CeCr4Al8, YFe4Al8, YCr4Al8, YMn4Al8, UCu4Al8, LaAg6In6, and PrAg6In6, which have ThMn12 structure. It is shown that at a certain temperature, characteristic for each compound with Fe, Cr, and Mn, below the Néel temperature a jump is observed in the total impedance and specific heat. At lower temperatures a negative magnetoresistance is observed in these compounds in weak magnetic fields. Superconducting phases are found in the compounds ScFe4Al8 (Tc=6 K), YCr4Al8 (Tc=4.5 K), YFe4Al8 (Tc=6 K), and PrAg6In6 (Tc=8.3 K).

The anisotropy of the electrical resistivity of YFe4Al8 and ScFe4Al8 single crystals is investigated for the first time in the frequency range 0–108 Hz and temperature range 300–4.2 K. It is found that the conductivity is higher along the growth axis of the crystals than in the perpendicular direction, while the parameters governing the antiferromagnetic ordering, negative magnetoresistance, and superconductivity effects observed in these single crystals are isotropic. Some effects known previously for polycrystalline high-Tc superconductors containing magnetic impurities are observed in the single crystals investigated and are found to be anisotropic in them.

Temperature dependences of low-frequency impedance (0–107 Hz) and heat capacity of LuFe4Al8 are studied at low temperature in the intervals 4.5–300 K and 1.5–120 K, respectively. The observed singularities suggest that antiferromagnetic phase ordering occurs at TN=100.5 K. A sharp increase in the resistance is observed at a certain temperature T1<TN below which a negative magnetoresistive effect is detected in a weak magnetic field (H<50 Oe). It is shown that the low- temperature anomalies at T<25 K are associated with the superconducting transition. This is supported by the presence of the Meissner effect, levitation, a decrease in ohmic losses, as well as the influence of a static magnetic field and direct current on the resistance of the compound. A magnetostructural phase transition, which is assumed to occur at T1<TN, may be responsible for the peculiarities observed in the physical properties of LuFe4Al8.