MAGNETIC PHASE-DIAGRAM OF THE U(NI1-XCUX)2GE2 SYSTEM STUDIED BY AC-SUSCEPTIBILITY MEASUREMENTS AND NEUTRON-DIFFRACTION OF POLYCRYSTALLINE SAMPLES

Polycrystalline U(Ni1-xCux)2Ge2 solid solutions, investigated by ac-susceptibility measurements and neutron diffraction, exhibit the ThCr2Si2-type crystallographic structure and magnetic ordering of the uranium sublattice, with moments along the tetragonal axis: antiferromagnetic type-I (AF-I) [k = (0, 0, 1)] for x = 0, 0.25, and 0.50; ferromagnetic below T(C), becoming at T0 (< T(C)): AF-I, ferrimagnetic [k = (0, 0, 2/3)], and AF-IA [k = (0, 0, 1/2)] for x = 0.75, 0.90, and 0.95, respectively; and ferromagnetic for x=l. The magnetic phase diagram (temperature versus composition) of the U(Ni1-xCux)2Ge2 system is proposed, and is discussed in relation to the variation in the number of conduction electrons (via Ruderman-Kittel-Kasuya-Yosida-type interactions).