Evolution of quadrupolar and magnetic order in a double perovskite solid solution Ba₂(Cd_1−xCa_x)ReO₆

Multipolar order is one of the representative electronic states realized in a spin-orbit entangled electronic state of 5d transition metal oxides. Recently, quadrupole and octupole orders have been discussed in 5d double perovskites Ba₂MgReO₆ and Ba₂NaOsO₆, respectively [1,2]. One can expect a richer variety of multipole ordres if the interactions between 5d electrons can be arbitrarily controlled.

In this study, we investigated the change in quadrupolar and magnetic states by substituting a larger Ca ion with Cd ion in Ba₂CdReO₆, which hosts quadrupolar order below T_q = 25 K and canted antiferromagnetic (AFM) order below T_m = 12 K [3]. With increasing Ca content x in Ba₂(Cd_1−xCa_x)ReO₆, the canted AFM phase is systematically suppressed and changes to AFM phase without a net moment above x = 0.6. The T_q is also suppressed with increasing x, however, the quadrupolar order survives up to x = 0.9. The obtained phase diagram nicely reproduces that proposed by the privious theoretical study [4]. Our results demonstrate that the electronic interactions can be finely controlled by chemical substitution, which may lead to the discovery of novel multipole orders.

[1] D. Hirai et al., Phys. Rev. Res. 2, 022063(R) (2020).

[2] D. Maharaj et al., Phys. Rev. Lett. 124, 087206 (2020).

[3] D. Hirai et al., J. Phys.: Condens. Matter 33, 135603 (2021).

[4] G. Chen et al Phys. Rev. B 82, 174440 (2010).