Possible quadrupole order in tetragonal BaCdReOand chemical trend in the ground states of 5double perovskites.

The synthesis and physical properties of the double perovskite (DP) compound BaCdReOwith the 5electronic configuration are reported. Three successive phases originating from a spin-orbit-entangled= 3/2 state, confirmed by a reduced effective magnetic moment of 0.72 , were observed upon cooling. X-ray diffraction measurements revealed a structural transition from a high-temperature cubic structure to a low-temperature tetragonal structure at= 170 K, below which the= 3/2 state was preserved. Magnetization, heat capacity, and thermal expansion measurements showed two more electronic transitions to a possible quadrupole ordered state at= 25 K and an antiferromagnetic order of dipoles with a ferromagnetic moment of ∼0.2 at= 12 K. These properties were compared with those of the DP's sister compounds BaReO(= Mg, Zn, and Ca) and the chemical trend is discussed in terms of the mean-field theory for spin-orbit-coupled 5electrons (2010 Chen174440). The DP BaReOcompounds provide a unique opportunity for a systematic investigation of symmetry breaking in the presence of multipolar degrees of freedom.