Chiral Order and Multiferroic Domain Relaxation in NaFeGe$_2$O$_6$

TL;DR

This study investigates the magnetic and multiferroic properties of NaFeGe$_2$O$_6$, revealing complex spin structures, domain control via electric fields, and relaxation dynamics consistent with Arrhenius-Merz behavior, advancing understanding of multiferroic domain dynamics.

Contribution

It provides new insights into the spin structure, domain control, and relaxation mechanisms of NaFeGe$_2$O$_6$, including the temperature-dependent multiferroic domain inversion and its dynamic behavior.

Findings

Incommensurate spiral order develops an additional component below 5 K.

Multiferroic domains are controllable and invertible by electric fields at low temperatures.

Domain wall motion speed is comparable to spin wave velocity.

Abstract

The magnetic structure and the multiferroic relaxation dynamics of NaFeGe$_2$O$_6$ were studied by neutron scattering on single crystals partially utilizing polarization analysis. In addition to the previously reported transitions, the incommensurate spiral ordering of Fe$^{3+}$ moments in the $ac$ plane develops an additional component along the crystallographic $b$ direction below $T\approx 5\text{ K}$, which coincides with a lock-in of the incommensurate modulation. The quasistatic control of the spin-spiral handedness, respectively of the vector chirality, by external electric fields proves the invertibility of multiferroic domains down to the lowest temperature. Time-resolved measurements of the multiferroic domain inversion in NaFeGe$_2$O$_6$ reveal a simple temperature and electric-field dependence of the multiferroic relaxation that is well described by a combined Arrhenius-Merz relation, as it has been observed for TbMnO$_3$. The maximum speed of domain wall motion is comparable to the spin wave velocity.