Non-collinear Magnetic Order in the Double Perovskites: Double Exchange on a Geometrically Frustrated Lattice

TL;DR

This paper investigates the complex magnetic phases in three-dimensional double perovskites, revealing non-collinear and frustrated magnetic orders driven by geometric frustration and electron delocalization.

Contribution

It provides a comprehensive analysis of magnetic ground states and transition temperatures in 3D double perovskites, highlighting the role of geometric frustration in non-collinear magnetic phases.

Findings

Identification of non-collinear spiral states and flux phases in 3D double perovskites.

Mapping of magnetic phase diagrams based on electron density and hopping parameters.

Demonstration of geometric frustration effects on magnetic ordering in FCC lattices.

Abstract

Double perovskites of the form A_2BB'O_6 usually involve a transition metal ion, B, with a large magnetic moment, and a non magnetic ion B'. While many double perovskites are ferromagnetic, studies on the underlying model reveal the possibility of antiferromagnetic phases as well driven by electron delocalisation. In this paper we present a comprehensive study of the magnetic ground state and T_c scales of the minimal double perovskite model in three dimensions using a combination of spin-fermion Monte Carlo and variational calculations. In contrast to two dimensions, where the effective magnetic lattice is bipartite, three dimensions involves a geometrically frustrated face centered cubic (FCC) lattice. This promotes non-collinear spiral states and `flux' like phases in addition to collinear anti-ferromagnetic order. We map out the possible magnetic phases for varying electron density, `level separation' epsilon_B - epsilon_B', and the crucial B'-B' (next neighbour) hopping t'.