Multiferroic domain relaxation in (NH4)2[FeCl5(H2O)]

TL;DR

This study investigates the domain relaxation dynamics in the multiferroic compound (NH4)2[FeCl5(H2O)] using neutron diffraction, revealing a slower relaxation process and complex magnetic ordering that does not affect domain wall pinning.

Contribution

It provides the first detailed analysis of multiferroic domain kinetics in (NH4)2[FeCl5(H2O)] and compares its relaxation behavior with other multiferroics, highlighting unique magnetic properties.

Findings

Multiferroic relaxation follows the Arrhenius-Merz law but with a larger time scale.

Higher-order magnetic contributions emerge upon cooling in the multiferroic phase.

Magnetic anharmonicity does not influence domain wall pinning or relaxation temperature dependence.

Abstract

The molecular compound (NH4)2[FeCl5(H2O)] is a type-II multiferroic material, in which incommensurate cycloidal order directly induces ferroelectric polarization. The multiferroic domain kinetics in (NH4)2[FeCl5(H2O)] were studied by time-resolved neutron diffraction experiments utilizing neutron polarization analysis. The temperature and electric-field dependent multiferroic relaxation obeys the simple combined Arrhenius-Merz law, which was reported to describe domain kinetics in the prototype multiferroics TbMnO3 and NaFeGe2O6. However, the characteristic time scale of the multiferroic relaxation is considerably larger than those in TbMnO3 or NaFeGe2O6. Temperature-dependent diffraction on (NH4)2[FeCl5(H2O)] reveals the emergence of higher-order and commensurate magnetic contributions upon cooling in the multiferroic phase in zero field. The good agreement with studies of higher-harmonic contributions in the deuterated material indicates that the isotopes only posses a minor impact on the magnetic ordering. But in contrast to similar observations in multiferroic MnWO4, this anharmonic modification of magnetic ordering does not depin multiferroic domain walls or alter the temperature dependence of the multiferroic relaxation.