cations direct magnetic interactions in double perovskites*

The main magnetic interaction in oxides is superexchange mediated by oxygen anions. Recently, it has been shown that diamagnetic d¹⁰ and d⁰ cations can play a role in extended superexchange interactions due to differences in orbital hybridization. Here we formulate simple rules for this d¹⁰/d⁰ effect in A₂B'B''O₆ double perovskite oxides. We have investigated magnetic interactions in cubic Mn²⁺ double perovskites Ba₂MnTeO₆ (d¹⁰ Te⁶⁺) and Ba₂MnWO₆ (d⁰ W⁶⁺). Our analysis reveals d¹⁰ cations on the B'' site promote strong J₁ interactions, while d⁰ cations promote J₂ interactions. This effect is general to 3d transition metal double perovskites. The d¹⁰/d⁰ effect can be used to tune magnetic interactions and ground states as we have previously shown for Sr₂CuTe_1-xW_xO₆, where the ground state can be tuned from magnetic order to a random singlet state.

[1] M. Zhu et al., Phys. Rev. Lett. 113, 076406 (2014).
[2] O. H. J. Mustonen et al., Chem. Mater. 32, 7070 (2020).
[3] H. Mutch et al., Phys. Rev. Mater. 4, 014408 (2020).
[4] O. Mustonen et al., Nat. Commun. 9, 1085 (2018).
[5] O. Mustonen et al., Phys. Rev. B 98, 064411 (2018).
[6] V. M. Katukuri et al., Phys. Rev. Lett. 124, 077202 (2020).