Theory of high T_c ferrimagnetism in a multiorbital mott insulator

We propose a model for the multiorbital material Sr₂CrOsO ₆, an insulator with remarkable magnetic properties and the highest T_c 725 K among all perovskites with a net moment. We derive a new criterion for the Mott transition (U₁U₂) ^1/2>2.5W by using slave-rotor mean field theory, where W is the bandwidth and U₁₍₂₎ are the effective Coulomb interactions on Cr(Os) including Hund's coupling. We show that Sr₂CrOsO₆ is a Mott insulator, where the large Cr U₁ compensates for the small Os U₂. The spin sector is described by a frustrated antiferromagnetic Heisenberg model that naturally explains the net moment arising from canting and also the observed nonmonotonic magnetization M(T). We predict characteristic magnetic structure factor peaks that can be probed by neutron experiments.