Effect of frustrations on magnetism in the Ru double perovskite Sr2YRuO6

Localized Ru⁵⁺ spins in Sr₂YRuO₆ form a fcc lattice with an antiferromagnetic (AFM) nearest-neighbor (NN) coupling J≈25 meV and rather low Néel temperature T_N=26 K. Analysis of the electronic structure of Sr₂RuO₄ results in the effective Heisenberg model. We have studied the effect of frustrations on the AFM type-I structure of Sr₂YRuO₆ in the spin-wave approximation. In the model with only NN coupling the AFM state is unstable due to frustrations, and T_N=0. Stabilization of the AFM state occurs due to the next-nearest-neighbor coupling I or due to the magnetic anisotropy D. Very small values D/J∼I/J⩽10^-3 are enough to obtain the experimental values of T_N and sublattice magnetization m=1.85μ_B/Ru (62% from the nominal S=3/2 value).