Magnetic and orbital order in overdoped bilayer manganites

TL;DR

This paper models magnetic and orbital orders in overdoped bilayer manganites, showing how static distortions and orbital interactions influence the phase diagram and magnetic structures.

Contribution

It introduces a comprehensive model incorporating two $e_g$ orbitals, Coulomb interactions, and lattice distortions to explain observed phases in bilayer manganites.

Findings

Reproduces the phase diagram for doping $0.5 < x < 1.0$.

Identifies the C-type magnetic phase as a natural outcome of layered geometry.

Shows orbital order drives magnetic order, influenced by lattice distortions.

Abstract

The magnetic and orbital orders for the bilayer manganites in the doping region $0.5 < x <1.0$ have been investigated from a model that incorporates the two $e_g$ orbitals at each Mn site, the inter-orbital Coulomb interaction and lattice distortions. The usual double exchange operates via the $e_g$ orbitals. It is shown that such a model reproduces much of the phase diagram recently obtained for the bilayer systems in this range of doping. The C-type phase with ($\pi,0,\pi$) spin order seen by Ling et al. appears as a natural consequence of the layered geometry and is stabilised by the static distortions of the system. The orbital order is shown to drive the magnetic order while the anisotropic hopping across the $e_g$ orbitals, layered nature of the underlying structure and associated static distortions largely determine the orbital arrangements.