Abstract: Neutron diffraction on the double perovskite Sr2YRuO6 with a quasi-fcc lattice of Ru moments reveals planar magnetic correlations that condense into a partial long-range ordered state with coupled alternate antiferromagnetic (AFM) YRuO4 square layers coexisting with the short-range correlations below T-N1 = 32 K. A second transition to a fully ordered AFM state below T-N2 = 24 K is observed. The reduced dimensionality of the spin correlations is arguably due to a cancellation of the magnetic coupling between consecutive AFM square layers in fcc antiferromagnets, which is the simplest three-dimensional frustrated magnet model system Ver menos