Magnetoelectric properties of $A_2$[FeCl$_5$(H$_2$O)] with $A = $ K, Rb, Cs

TL;DR

This study identifies and characterizes new linear magnetoelectric materials in the $A_2$[FeCl$_5$(H$_2$O)] family with $A=$ K, Rb, Cs, revealing their magnetic symmetries and phase diagrams through detailed measurements.

Contribution

It provides the first detailed investigation of the magnetoelectric properties and magnetic symmetry analysis of these compounds, including the development of a magnetic structure model for the Cs-based material.

Findings

K- and Rb-based compounds show anisotropic linear magnetoelectric effects.

Magnetic point groups are identified as $m'm'm'$ for K/Rb and $mmm'$ for Cs.

Magnetic-field versus temperature phase diagrams are established.

Abstract

The compounds $A_2$[FeCl$_5$(H$_2$O)] with $A=$ K, Rb, Cs are identified as new linear magnetoelectric materials. We present a detailed investigation of their linear magnetoelectric properties by measurements of pyroelectric currents, dielectric constants and magnetization. The anisotropy of the linear magnetoelectric effect of the K-based and Rb-based compound is consistent with the magnetic point group $m'm'm'$, already reported in literature. A symmetry analysis of the magnetoelectric effect of the Cs-based compound allows to determine the magnetic point group $mmm'$ and to develop a model for its magnetic structure. In addition, magnetic-field versus temperature phase diagrams are derived and compared to the closely related multiferroic (NH$_4$)$_2$[FeCl$_5$(H$_2$O)].