Interplay of magnetic and structural transitions in Fe-based pnictide superconductors

TL;DR

This paper investigates how magnetic and structural phase transitions interact in Fe-based pnictide superconductors using a Ginzburg-Landau model, explaining observed phenomena and proposing experimental tests.

Contribution

It introduces a magnetoelastic coupling framework that explains transition features and magnetic ordering collinearity in these superconductors.

Findings

Magnetoelastic coupling explains transition temperature coincidence.

Coupling determines the order of phase transitions.

Proposes an experimental criterion to distinguish transition types.

Abstract

The interplay between the structural and magnetic phase transitions occurring in the Fe-based pnictide superconductors is studied within a Ginzburg-Landau approach. We show that the magnetoelastic coupling between the corresponding order parameters is behind the salient features observed in the phase diagram of these systems. This naturally explains the coincidence of transition temperatures observed in some cases as well as the character (first or second-order) of the transitions. We also show that magnetoelastic coupling is the key ingredient determining the collinearity of the magnetic ordering, and we propose an experimental criterion to distinguish between a pure elastic from a spin-nematic-driven structural transition.