Magnetic and orbital order in the A-phase of manganites

The A-phase of La 1 - x Ca x MnO 3 , stable for small x, is studied using a mean-field slave–boson formulation for e g -electrons in two orbitals with excluded multiple occupancy. The classical t 2 g -spins are ordered ferromagnetically (F) in the xy planes, which are antiferromagnetically (AF) coupled along the z -direction. All 3d-electrons are coupled F via Hund's rule. The F double-exchange, competing with the AF superexchange, can lead to a lattice distortion via Jahn–Teller coupling of the e g -electrons to the lattice degrees of freedom. Conditions for staggered orbital long-range order are discussed.