Anisotropy study of multiferroicity in the pyroxene NaFeGe$_2$O$_6$

TL;DR

This study investigates the directional dependence of dielectric, magnetic, and magnetoelastic properties in the multiferroic NaFeGe$_2$O$_6$, revealing detailed phase diagrams and the influence of magnetic fields on electric polarization.

Contribution

It provides the first detailed analysis of anisotropic multiferroic behavior and phase diagrams of NaFeGe$_2$O$_6$, highlighting the triclinic symmetry of its multiferroic phase.

Findings

Electric polarization mainly in the ac plane below 11.6 K

Magnetic fields can significantly modify polarization

Identified three low-temperature multiferroic phases

Abstract

We present a study of the anisotropy of the dielectric, magnetic and magnetoelastic properties of the multiferroic clinopyroxene NaFeGe$_2$O$_6$. Pyroelectric currents, dielectric constants and magnetic susceptibilities as well as the thermal expansion and the magnetostriction were examined on large synthetic single crystals of NaFeGe$_2$O$_6$. The spontaneous electric polarization detected below $T_{\rm C}\simeq 11.6$ K in an antiferromagnetically ordered state ($T_{\rm N}\simeq 13$ K) is mainly lying within the $ac$ plane with a small component along $b$, indicating a triclinic symmetry of the multiferroic phase of NaFeGe$_2$O$_6$. The electric polarization can be strongly modified by applying magnetic fields along different directions. We derive detailed magnetic-field versus temperature phase diagrams and identify three multiferroic low-temperature phases, which are separated by a non-ferroelectric, antiferromagnetically ordered state from the paramagnetic high-temperature phase.