Possible quadrupole order in tetragonal Ba2CdReO6and chemical trend in the ground states of 5 d1double perovskites

Abstract

The synthesis and physical properties of the double perovskite (DP) compound Ba₂CdReO₆with the 5d¹electronic configuration are reported. Three successive phases originating from a spin-orbit-entangledJ_eff= 3/2 state, confirmed by a reduced effective magnetic moment of 0.72 μ_B, were observed upon cooling. X-ray diffraction measurements revealed a structural transition from a high-temperature cubic structure to a low-temperature tetragonal structure atT_s= 170 K, below which theJ_eff= 3/2 state was preserved. Magnetization, heat capacity, and thermal expansion measurements showed two more electronic transitions to a possible quadrupole ordered state atT_q= 25 K and an antiferromagnetic order of dipoles with a ferromagnetic moment of ∼0.2 μ_BatT_m= 12 K. These properties were compared with those of the DP's sister compounds Ba₂BReO₆(B= Mg, Zn, and Ca) and the chemical trend is discussed in terms of the mean-field theory for spin-orbit-coupled 5delectrons (2010 Chenet al Phys. Rev. B82174440). The DP Ba₂BReO₆compounds provide a unique opportunity for a systematic investigation of symmetry breaking in the presence of multipolar degrees of freedom.

Keywords: Ba2CdReO6; double perovskite; multipolar order; quadrupole order; spin–orbit interaction.