Magnetic-Field-Induced Change of Magneto-Electric Coupling in the in Molecular Multiferroic (ND4)2[FeCl5(D2O)]

TL;DR

This study investigates how an external magnetic field alters the magneto-electric coupling mechanisms in a molecular multiferroic, revealing a transition from spin current to p-d hybridization as the dominant process.

Contribution

It reports the first observed sequence of magneto-electric coupling mechanisms changing with magnetic field in (ND4)2[FeCl5(D2O)].

Findings

Magnetic structures evolve from incommensurate to quasi-collinear with field.

Different coupling mechanisms operate below and above 5 T.

The compound exhibits a unique transition between two magneto-electric mechanisms.

Abstract

Our results describe an unprecedented example of change in the mechanism of magnetically-induced electric polarization from spin current to spin-dependent p-d hybridization model. We have followed the evolution of the magnetic structures of (ND4)2[FeCl5 D2O] compound using single crystal neutron diffraction under external magnetic field. The spin arrangements change from incommensurate cycloidal to commensurate distorted-cycloidal and finally to quasi-collinear. The determination of the magnetic structures allows us to explain the observed electric polarization in the different ferroelectric phases. Two different magneto-electric coupling mechanisms are at play: the spin-current mechanism for external magnetic field below 5 T, and the spin dependent p-d hybridization mechanism for magnetic field above this value, being this compound the first example reported presenting this sequence of magneto-electric coupling mechanisms.