We have studied the magnetic behaviour of PrAu2(Si1-xGex)2 by means of magnetic susceptibility, resistivity, and heat capacity measurements, and x-ray and neutron powder diffraction. All compounds are isostructural and crystallize in the well known ThCr2Si2-type structure. PrAu2Si2 shows the characteristic features of a canonical spin glass with a freezing temperature of TF = 3 K. Completely unexpectedly, on introducing/increasing the atomic disorder by alloying with Ge, the spin-glass transition is suppressed as is first evident from a slight decrease of the freezing temperature TF up to x = 0.10. Long-range magnetic order sets in for x0.12. Within the range 0.15 x1, all compounds show the same simple AF-I-type antiferromagnetic structure with a monotonic increase of both the Néel temperature and the ordered magnetic moment for increasing Ge concentration. The magnetic phase diagram of PrAu2(Si1-xGex)2 is explained by the presence of weak disorder at a constant level at the Au sites. Clear indications of crystal-field effects have been observed.

The ferroelectric insulator BaTiO 3 can be electron-doped by substitution of divalent Ba 2ϩ with trivalent La 3ϩ , creating d states at the transition-metal sites. The successive filling of the 3d Ti band initiates a sequence of electronic transitions. First, the system undergoes an Anderson-type insulator-to-metal-transition into a paramagnetic and metallic state, and second, a correlation-induced antiferromagnetic and insulating phase is established for La-rich concentrations. Ceramic La 1Ϫx Ba x TiO 3 samples covering the whole concentration range were systematically examined utilizing measurements of resistivity, specific heat, and magnetic susceptibility in the temperature range 1.8ϽTϽ300 K. The concentration dependence of the Sommerfeld coefficient ␥ and the Pauli spin susceptibility was systematically investigated. The temperature dependence of the resistivity was studied in detail. In addition a (T,x) phase diagram of La 1Ϫx Ba x TiO 3 was constructed.