Magnetism in some UCo1/3T2/3Al solid solutions (T=transition metal)

We report on the magnetic properties of UCo1/3T2/3Al (T=Ru, Rh, Pt) solid s olutions which form in the hexagonal ZrNiAl structure. We performed neutron diffraction and bulk magnetization studies. All three solid solutions exhi bit long-range magnetic order at low temperatures. Bulk magnetization studi es indicate a ferromagnetic ground state for UCo1/3Ru2/3Al, UCo1/3Rh2/3Al, and UCo1/3Pt2/3Al below 42, 41, and 27 K, respectively. At 4.2 K, the spont aneous moment ranges from similar to 0.15 mu(B)/U-atom (UCo1/3Ru2/3Al) to s imilar to 0.49 mu(B)/U-atom (UCo1/3Pt2/3Al). Below T-C, we find additional weak magnetic contributions in the neutron diffraction data, and our refine ment is consistent with magnetic moments along the c axis. The magnitudes o f the moments are in good agreement with the spontaneous moments determined from bulk studies. The results are discussed in terms of f-d hybridization , which is modified by changes in the d band occupation and preferential oc cupation of the transition metals within the lattice. (C) 2000 American Ins titute of Physics. [S0021-8979(00)94108-2].