Multiferroicity in orthorhombic $R\mathrm{Mn}{\mathrm{O}}_3$ ($R=\mathrm{Dy},\mathrm{Tb}$, and $\mathrm{Gd}$) under high pressure

The hydrostatic pressure effect on multiferroic properties of rare-earth manganites $R\mathrm{Mn}{\mathrm{O}}_3$ ($R=\mathrm{Dy},\mathrm{Tb}$, and $\mathrm{Gd}$) with the $Pbnm$ orthorhombic structure was investigated by using a diamond anvil cell. Under high pressure, all of these manganites were found to exhibit ferroelectricity in which spontaneous polarization $(\approx {10}^0\mu \mathrm{C}/\mathrm{c}{\mathrm{m}}^2)$ develops along the $a$ axis. The application of a magnetic field $B$ along the $a$ axis to the high-pressure ferroelectric phase causes a drastic change in the electric polarization $P$. Especially in $\mathrm{GdMn}{\mathrm{O}}_3$, the $B$-induced change in $P$ reached $\Delta P\left(B\right)=1.3\mu \mathrm{C}/\mathrm{c}{\mathrm{m}}^2$. A possible origin of the observed $R$-dependent pressure effect is discussed.

Figure 1

Dielectric and ferroelectric properties of (a)–(c) $\mathrm{DyMn}{\mathrm{O}}_3$, (d)–(f) $\mathrm{TbMn}{\mathrm{O}}_3$, and (g)–(i) $\mathrm{GdMn}{\mathrm{O}}_3$ at various pressures. The left panels show the temperature dependence of the relative dielectric constant ${\varepsilon }^{\prime }$ normalized by the value at 60 K. The right panels represent electric polarization as a function of applied electric field at selected pressures and temperatures. All the measurements were done with $E\parallel a$ at 0 T. The data of $\mathrm{TbMn}{\mathrm{O}}_3$ are taken from Ref. [9]. The upper and lower insets of (d) show schematic drawings of the $bc$ cycloidal spiral and the $E$-type AFM structures, respectively.

Figure 2

Dielectric and ferroelectric properties in the high-pressure phase of (a)–(c) $\mathrm{DyMn}{\mathrm{O}}_3$, (d)–(f) $\mathrm{TbMn}{\mathrm{O}}_3$, and (g)–(i) $\mathrm{GdMn}{\mathrm{O}}_3$ at several magnetic fields. The left panels show the temperature dependence of relative dielectric constant ${\varepsilon }^{\prime }$. The right panels represent electric polarization as a function of applied electric field at selected pressures, temperatures, and magnetic fields. Both $E$ and $B$ were applied along the $a$ axis.

Figure 3

Magnetodielectric effect at $5\mathrm{K}(<T_{\mathrm{N}}^R)$ in the low-pressure (red curves) and high-pressure (blue curves) phases of (a) $\mathrm{DyMn}{\mathrm{O}}_3$, (b) $\mathrm{TbMn}{\mathrm{O}}_3$, and (c) $\mathrm{GdMn}{\mathrm{O}}_3$. (d) Magnetoelectric effect at 5 K in the high-pressure phase of these manganites. Both $E$ and $B$ were applied along the $a$ axis.

Figure 4

The spontaneous polarization as a function of pressure at several temperatures in magnetic fields of 0 T (left panels) and 8 T (right panels) for $\mathrm{DyMn}{\mathrm{O}}_3$ (top), $\mathrm{TbMn}{\mathrm{O}}_3$ (middle), and $\mathrm{GdMn}{\mathrm{O}}_3$ (bottom).