Antiferromagnetic order in the honeycomb Kondo lattice CePt6Al3 induced by Pd substitution

The cerium-based compound CePt6Al3, in which Ce atoms form a honeycomb lattice hosting magnetic frustration, has a heavy-fermion ground state. We have observed development of magnetic order in partially Pd-substituted Ce(Pt1-xPdx)6Al3 series up to x = 0.3 by the measurements of magnetic susceptibility, electrical resistivity ρ, and specific heat C. In the whole range of x, the unit cell volume remains unchanged within 0.2%, and the effective magnetic moment stays at 2.4μB/Ce. For x = 0.05, both C/T and ρ(T) jump on cooling at Tm=1.8K. With increasing x to 0.2, Tm increases to 3.8 K, where C/T shows a pronounced λ-type anomaly. Application of magnetic fields suppresses Tm, which is indicative of an antiferromagnetic (AFM) ordered state. Thus, a long-range AFM order is induced by the substitution of isovalent Pd for Pt in CePt6Al3 without carrier doping and chemical pressure. We attribute the emergence of AFM order in Ce(Pt1-xPdx)6Al3 to the randomness in the spin-orbit interaction in the Pt-Pd sublattice, which weakens both the coherent Kondo effect and magnetic frustration in the honeycomb Kondo lattice.