Topology of the Spin-polarized Charge Density in bcc and fcc Iron

TL;DR

This paper explores the topology of spin-polarized charge densities in bcc and fcc iron, revealing unique topologies and their relation to magnetic phase transitions, including topological catastrophes.

Contribution

It uncovers distinct topological features of spin densities in iron and links these to different magnetic phase transitions, offering new insights into magnetic behavior.

Findings

Spin-density topology in iron varies with magnetic phase.

High-spin fcc iron exhibits unique topologies not seen in non-magnetic materials.

A topological catastrophe is associated with the low-spin to high-spin transition.

Abstract

We investigate the topology of the spin-polarized charge density in bcc and fcc iron. While the total spin-density is found to possess the topology of the non-magnetic prototypical structures, in some cases the spin-polarized densities are characterized by unique topologies; for example, the spin-polarized charge densities of bcc and high-spin fcc iron are atypical of any known for non-magnetic materials. In these cases, the two spin-densities are correlated: the spin-minority electrons have directional bond paths with deep minima in the minority density, while the spin-majority electrons fill these holes, reducing bond directionality. The presence of two distinct spin topologies suggests that a well-known magnetic phase transition in iron can be fruitfully reexamined in light of these topological changes. We show that the two phase changes seen in fcc iron (paramagnetic to low-spin and low-spin to high-spin) are different. The former follows the Landau symmetry-breaking paradigm and proceeds without a topological transformation, while the latter also involves a topological catastrophe.