Magnetic frustration in double perovskite LaSrNiRuO₆

Using density functional calculations, we investigated the electronic structure and magnetism of the newly synthesized antiferromagnetic (AF) double perovskite LaSrNiRuO₆. Our results show that the first nearest-neighbouring (1NN) Ni²(t_2g ⁶e_g ², S = 1) and ions have a ferromagnetic (FM) coupling. However, we find that LaSrNiRuO₆ displays long-range magnetic interactions: the second nearest-neighbouring (2NN) Ru-Ru AF coupling and the 2NN Ni-Ni AF coupling are both stronger than the 1NN Ni-Ru FM coupling, and the third nearest-neighbouring (3NN) Ru-Ru and Ni-Ni AF couplings are also considerably large. Thus, the leading Ru-Ru and Ni-Ni AF interactions in the face-centered-cubic (fcc) sublattices give rise to a magnetic frustration, and eventually determine a distorted low-temperature AF order. This work addresses the importance of long-range magnetic interactions in determining the exotic magnetic structure of double perovskites.