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) $\text{Ni}^{2+}(t_{2g}^{6}e_{g}^{2},S=1)$ and $\text{Ru}^{5+}(t_{2g}^{3},S=3/2)$ 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.