The Effect of $f$-$d$ Magnetic Coupling in Multiferroic $R$MnO$_3$ Crystals

TL;DR

This study investigates how different rare earth 4f magnetic moments influence the magnetoelectric phases in multiferroic $R$MnO$_3$ crystals, revealing that the magnetic nature of the rare earth ions significantly alters their ferroelectric properties.

Contribution

The paper provides detailed phase diagrams showing the distinct effects of Tb and Gd substitutions on the magnetoelectric phases of $R$MnO$_3$, highlighting the role of 4f moments.

Findings

Tb substitution destroys $P_a$ ferroelectric phase at low x

Increasing Tb stabilizes the $P_c$ phase

Gd substitution suppresses $P_c$ and slightly reduces $P_a$

Abstract

We have established detailed magnetoelectric phase diagrams of (Eu$_{0.595}$Y$_{0.405}$)$_{1-x}$Tb$_x$MnO$_3$ ($0 \le x \le 1$) and (Eu,Y)$_{1-x}$Gd$_x$MnO$_3$ ($0 \le x \le 0.69$), whose average ionic radii of $R$-site ($R$: rare earth) cations are equal to that of Tb$^{3+}$, in order to reveal the effect of rare earth 4$f$ magnetic moments on the magnetoelectric properties. In spite of the same $R$-site ionic radii, the magnetoelectric properties of the two systems are remarkably different from each other. A small amount of Tb substitution on $R$ sites ($x \sim 0.2$) totally destroys ferroelectric polarization along the a axis ($P_a$), and an increase in Tb concentration stabilizes the $P_c$ phase. On the other hand, Gd substitution ($x \sim 0.2$) extinguishes the $P_c$ phase, and slightly suppresses the $P_a$ phase. These results demonstrate that the magnetoelectric properties of $R$MnO$_3$ strongly depend on the characteristics of the rare earth 4$f$ moments.