title: Insulating ferromagnetism in La4Ba2Cu2O10: an Ab initio wannier function analysis.
abstract: Microscopic mechanisms of the puzzling insulating ferromagnetism of half-filled La4Ba2Cu2O10 are elucidated with energy-resolved Wannier states. The dominant magnetic coupling, revealed through evaluated parameters (t, U, and J), turns out to be the intersite direct exchange, a currently ignored mechanism that overwhelms the antiferromagnetic superexchange. By contrast, the isostructural Nd4Ba2Cu2O10 develops the observed antiferromagnetic order via its characteristics of a 1D chain. Surprisingly, the in-plane order of both cases is not controlled by coupling between nearest neighbors. An intriguing pressure-induced ferromagnetic to antiferromagnetic transition is predicted.
authors.affiliation: Department of Physics, University of California, Davis 95616-8677, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Ku
authors.forename: H
authors.initials: H
authors.lastname: Rosner
authors.forename: W E
authors.initials: WE
authors.lastname: Pickett
authors.forename: R T
authors.initials: RT
authors.lastname: Scalettar