Spin excitations in ferromagnetic manganites with orbital order

Abstract

The ferromagnetic metallic phase of doped cubic manganites with orbital order is investigated in a two-band double exchange model extended by Jahn–Teller (JT) terms. Evaluating the spin wave self-energy in the lowest order 1/S expansion, one finds that spin excitations are anisotropic and depend on the type of occupied eg orbitals. In the case of a small splitting between eg orbital energies, magnon dispersion exhibits a pronounced asymmetry between low and high hole doping, while a strong JT effect leads to the alternating orbital order which can reduce the spin stiffness by one order of magnitude. For a bilayer system, the kinetic energy induces an x2 − y2 orbital character and is responsible for a drastic change in the interplane exchange coupling in the doping range 0.3 < x < 0.5.