Magnetic order in CePd_1-xNi_xAl

CePd_1-xNi_xAl is a heavy-fermion system, which shows both, geometric frustration arising from the hexagonal crystal structure and quantum critical behavior. By substituting palladium with nickel the Neel temperature of T_N = 2.7 K in CePdAl can be suppressed to zero at a nickel concentration of 14 %, where an antiferromagnetic quantum critical point is reached. Due to the combination of magnetic frustration and quantum criticality CePd_1-xNi_xAl may be a model system for investigating the influence of frustration on quantum critical behavior. To study the evolution of magnetic order in the substitution series detailed heat capacity measurements under magnetic fields were performed. The resulting phase diagrams for magnetic fields applied along the easy axis will be shown and discussed for CePdAl, the 5 %- and 10 %-nickel substituted system. A suppression of the Neel temperature as well as of the critical magnetic field are observed. In contrast to CePdAl no additional antiferromagnetic phases were detected in the Ni-alloyed systems. Furthermore, magnetic phase diagrams for fields applied along the hard ab-plane were established. Due to the frustration a slight increase of the ordering temperature was observed for small magnetic fields B<1 T.