Field-induced Orbital Patterns in Ferromagnetic Layered Ruthenates

TL;DR

This paper investigates how external magnetic fields influence orbital patterns in ferromagnetic layered ruthenates, revealing field-direction-dependent transitions between orbital ordered and disordered states through exact diagonalization methods.

Contribution

It introduces a detailed phase diagram showing how orbital configurations in ruthenates respond to external fields and lattice distortions, highlighting the activation of specific orbital states.

Findings

Field along easy axis induces orbital order with ferro-orbital correlations.

Field along hard axis suppresses orbital order by reducing local orbital moments.

External fields activate different orbital configurations depending on their direction.

Abstract

We study the evolution of orbital patterns in ferromagnetic layered ruthenates due to the competition of Coulomb interactions, compressive c axis and orthorhombic distortions in the presence of a polarizing orbital field coupled to the angular momentum. By means of the exact diagonalization on a 2x2 cluster and a cluster embedded analysis where inter-plaquette interaction is treated on mean field level, we determine the ground-state phase diagram. Specifically, we demonstrate that, via the activation of two or three of t_2g local orbital configurations, an external field applied along different symmetry directions can lead to inequivalent orbital correlated states. Starting from an antiferro-orbital pattern, for the easy axis case an orbital ordered phase is induced, having strong next nearest neighbors ferro-orbital correlations. Otherwise, a field applied along the hard axis leads a reduction of local orbital moment in a way to suppress the orbital order.