STRUCTURE, MAGNETIC AND ELECTRICAL-PROPERTIES OF THE UMN4-XFEXAL8 SYSTEM

UMn4Al8 is paramagnetic, however, it seems to be on the verge of magne tic ordering. Therefore, it is interesting to check if an admixture of Fe can induce a magnetic ordering in the U and Mn sublattices. The UM n4-xFexAl8 system exists in the whale concentration range 0 less than or equal to x less than or equal to 4. The lattice parameters follow r oughly Vegard's law. Magnetic susceptibility, which is measured at T=1 .8-300 K in a magnetic field of 0.5 T, fulfils the Curie-Weiss law abo ve 100 K for x=1 and 2, and above 150 K for x=3; however, the values o f the effective magnetic moment and the paramagnetic Curie temperature have only the meaning of the material constants. Below 100 K, the tem perature dependence of magnetic susceptibility exhibits anomalies whic h can be related to magnetic ordering of different sublattices (Fe,U,M n?). Magnetization measurements at 4.2 K in magnetic fields up to 40 T (pulsed held) show a hysteresis and saturation that indicate a ferro( ferri)magnetic character of the ordering. The electric resistivity cur ves versus temperature show a shape which is far from a typical metall ic behavior. Magnetoresistivity curves are similar to those observed f or UFe4Al8. (C) 1998 Elsevier Science S.A.