Theory of High T\(_c\) Ferrimagnetism in a Multi-orbital Mott Insulator

Abstract

We propose a model for the multi-orbital material Sr\(_2\)CrOsO\(_6\) (SCOO), an insulator with remarkable magnetic properties and the highest \(T_c \simeq 725\) K among {\em all} perovskites with a net moment. We derive a new criterion for the Mott transition \((\widetilde{U}_{1} \widetilde{U}_{2})^{1/2}>2.5W\) using slave rotor mean field theory, where \(W\) is the bandwidth and \(\widetilde{U}_{1(2)}\) are the effective Coulomb interactions on Cr(Os) including Hund's coupling. We show that SCOO is a Mott insulator, where the large Cr \(\widetilde{U}_{1}\) compensates for the small Os \(\widetilde{U}_{2}\). The spin sector is described by a frustrated antiferromagnetic Heisenberg model that naturally explains the net moment arising from canting and also the observed non-monotonic magnetization \(M(T)\). We predict characteristic magnetic structure factor peaks that can be probed by neutron experiments.