Field induced spin reorientation and giant spin-lattice coupling in EuFe2As2

TL;DR

This study reveals field-induced spin reorientation and significant spin-lattice coupling in EuFe2As2, demonstrating a magnetic shape-memory effect and detailed magnetic phase behavior under external magnetic fields.

Contribution

The paper reports the first detailed neutron diffraction analysis of EuFe2As2 under magnetic fields, uncovering a reversible twinning realignment and spin-lattice coupling mechanisms.

Findings

Field-induced spin reorientation from antiferromagnetic to ferromagnetic states.

Magnetic field causes a ~0.9% strain via twinning realignment.

Reversible twinning realignment suggests magnetic shape-memory effect.

Abstract

We have studied a EuFe2As2 single crystal by neutron diffraction under magnetic fields up to 3.5 T and temperatures down to 2 K. A field induced spin reorientation is observed in the presence of a magnetic field along both the a and c axes, respectively. Above critical field, the ground state antiferromagnetic configuration of Eu$^{2+}$ moments transforms into a ferromagnetic structure with moments along the applied field direction. The magnetic phase diagram for Eu magnetic sublattice in EuFe2As2 is presented. A considerable strain ($\sim$0.9%) is induced by the magnetic field, caused by the realignment of the twinning structure. Furthermore, the realignment of the twinning structure is found to be reversible with the rebound of magnetic field, which suggested the existence of magnetic shape-memory effect. The Eu moment ordering exhibits close relationship with the twinning structure. We argue that the Zeeman energy in combined with magnetic anisotropy energy is responsible for the observed spin-lattice coupling.