Magnetoelectric Phase Diagrams Research Articles

Magnetic structure and magnetoelectric coupling in bulk and thin filmFeVO4

We have investigated the magnetoelectric and magnetodielectric response in FeVO$_4$, which exhibits a change in magnetic structure coincident with ferroelectric ordering at $T_{N2}$$\approx$15 K. Using symmetry considerations, we construct a model for the possible magnetoelectric coupling in this system, and present a discussion of the allowed spin structures in FeVO$_4$. Based on this model, in which the spontaneous polarization is caused by a trilinear spin-phonon interaction, we experimentally explore the magnetoelectric coupling in FeVO$_4$ thin films through measurements of the electric field induced shift of the multiferroic phase transition temperature, which exhibits an increase of 0.25 K in an applied field of 4 MV/m. The strong spin-charge coupling in \fvo\, is also reflected in the significant magnetodielectric shift, which is present in the paramagnetic phase due to a quartic spin-phonon interaction and shows a marked enhancement with the onset of magnetic order which we attribute to the trilinear spin-phonon interaction. We observe a clear magnetic field induced dielectric anomaly at lower temperatures, distinct from the sharp peak associated with the multiferroic transition, which we tentatively assign to a spin reorientation cross-over. We also present a magnetoelectric phase diagram for FeVO$_4$.

Magnetoelectric phase diagrams of orthorhombicRMnO3(R=Gd, Tb, and Dy)

Magnetoelectric phase diagrams have been investigated for rare-earth manganites with orthorhombically distorted perovskite structure, $R{\mathrm{MnO}}_{3}$ ($R=\mathrm{Gd}$, Tb, and Dy). A variety of magnetic and electric phases emerge with varying $R$-site ion, temperature, and magnetic field in these systems. The magnetoelectric phase diagram varies sensitively with the direction of a magnetic field relative to the crystallographic axes. Although the ground state of ${\mathrm{GdMnO}}_{3}$ with the largest ionic radius of $R({r}_{R})$ is not ferroelectric in zero magnetic fields $(H=0)$, a ferroelectric phase with electric polarization $(P)$ along the $a$ axis appears by applying $H(g\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{T})$ along the $b$ axis. Both ${\mathrm{TbMnO}}_{3}$ and ${\mathrm{DyMnO}}_{3}$ show a ferroelectric order with $P$ along the $c$ axis even at $H=0$ below a lock-in transition temperature where nonzero wave vectors for magnetic and lattice modulations become nearly constant. These systems also exhibit a flop of the ferroelectric polarization ($P\ensuremath{\Vert}c$ to $P\ensuremath{\Vert}a$) when $H$ is applied along the $a$ or $b$ axis. By contrast, the application of $H$ above $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ along the $c$ axis completely suppresses the ferroelectricity in ${\mathrm{TbMnO}}_{3}$. Possible origins of the observed evolution of magnetoelectric phases are discussed in consideration of magnetism and lattice distortion in the perovskite rare-earth manganites.