Giant uniaxial anisotropy in the magnetic and transport properties of CePd₅Al₂

Electrical resistivity ρ, magnetic susceptibility χ, magnetization M, and specific heat measurements are reported on a singlecrystalline sample of CePd₅Al₂, showing successive antiferromagnetic orderings at T_N1 = 4.1 K and T_N2 = 2.9 K. The temperature dependence of ρ shows a Kondo metal behavior with large anisotropy, ρ_c/ρ_a = 3.2 at 20 K, and opening of a superzone gap along the tetragonal c-direction below T_N1. Both T_N1 and T_N2 gradually increase with applying pressure up to 2.5 GPa. The data of χ(T) and M(B) in the paramagnetic state were analyzed using a crystalline electric field (CEF) model. It led to a Kramers doublet ground state with wave functions consisting primarily of |±5/2〉, whose energy level is isolated from the excited states by 230 and 300 K. This CEF effect gives rise to the large anisotropy in the paramagnetic state. In the ordered state, the uniaxial magnetic anisotropy is manifested as M_c/M _a = 20 in B = 5 T and at 1.9 K, and χ_c/χ _a = 25 in B = 0.1 T and at 4 K. In powder neutron diffraction experiments, magnetic reflections were observed owing to the antiferromagnetic ordered states below T_N1, whereas no additional reflection was found below T_N2.