Magnetic softness in iron-based superconductors

TL;DR

This paper investigates the microscopic origins of magnetic softness in iron-based superconductors, highlighting the role of Hund's rule coupling and the competition between ferromagnetic and antiferromagnetic interactions.

Contribution

It identifies the Hund's rule coupling strength as the key material-dependent parameter influencing magnetic ground states in these superconductors.

Findings

Hund's rule coupling strength varies among materials.

Magnetic softness results from competition between double-exchange and superexchange.

First-principles analysis links microscopic parameters to magnetic behavior.

Abstract

We examine the relevance of several major material-dependent parameters to the magnetic softness in iron-base superconductors by first-principles electronic structure analysis of their parent compounds. The results are explained in the spin-fermion model where localized spins and orbitally degenerate itinerant electrons coexist and are coupled by Hund's rule coupling. We found that the difference in the strength of the Hund's rule coupling term is the major material-dependent microscopic parameter for determining the ground-state spin pattern. The magnetic softness in iron-based superconductors is essentially driven by the competition between the double-exchange ferromagnetism and the superexchange antiferromagnetism.