Spontaneous reorientation of the electric polarization in Eu$_{1-x}$Ho$_x$MnO$_3$ multiferroics

The magnetic, dielectric, and ferroelectric properties of Eu$_{1-x}$Ho$_x$MnO$_3$ single crystals ($0<x\leq0.5$), where magnetic ordering can be varied from the canted antiferromagnetic phase to modulated spin structures, have been studied. It has been found that a ferroelectric state appears at $х\geq0.2$ and low temperatures. As the temperature decreases and the holmium content increases, the electric polarization in this state is reoriented from the $a$ axis to the $c$ axis. It has been shown that the polarization is reoriented owing to a change in the spin rotation plane in the cycloidal phase from the $ab$ to $cb$ plane because of the stabilization of the latter upon an increase in the rare-earth contribution to the anisotropy energy. The $T$–$x$ phase diagram of magnetic and ferroelectric states has been constructed.