Magnetism and magnetoelastic coupling in layered ruthenates

Various recent experimental investigations have identified the metallic bi-layer ruthenate Sr₃Ru₂O₇ as a paramagnet near a ferromagnetic instability, a ferromagnet with T_C above 100 K and a paramagnet with presumably antiferromagnetic ordering below 20 K. Here we present density functional investigations of the electronic structure and magnetic properties of this compound. We find quite strong magnetoelastic coupling so that the magnetic properties are highly sensitive to the crystal structure. With the initially reported tetragonal structure, we find Sr₃Ru₂O₇ to be on the verge of a ferromagnetic Stoner instability. However, using a recent neutron refined orthorhombic structure, it becomes magnetic. We find strong in-plane ferromagnetic couplings of an itinerant nature