This paper reports on structural, magnetic, dielectric, thermodynamic, and magnetodielectric properties of Eu${}_{1-x}$Lu${}_x$MnO${}_3$, with 0 ⩽ $x$ ⩽ 0.2, towards the ($x$, $T$) phase diagram. The phase diagram reflects the effect of lattice distortions induced by the isovalent substitution of Eu${}^{3+}$ by smaller Lu${}^{3+}$ ions, which gradually unbalances the antiferromagnetic against the ferromagnetic exchange interactions, enabling the emergence of both ferroelectricity and magnetoelectric coupling. For $x$ < 0.1, the paramagnetic phase is followed by a presumably incommensurate collinear antiferromagnetic phase AFM-1, and then a weak ferromagnetic phase seems to be established, with a canted $A$-type antiferromagnetic order. For 0.1 ⩽ $x$ ⩽ 0.2, the AFM-1 phase is followed by an antiferromagnetic phase AFM-2 with modulated spiral spin arrangement, compatible with ferroelectricity. The disappearance of hysteresis cycles $P$($E$) at low temperatures, clearly indicates the existence of an antiferromagnetic phase AFM-3, whose spin structure is not compatible with both the ferroelectric and ferromagnetic components. The magnetic behavior of EuMnO${}_3$ and Eu${}_{0.9}$Lu${}_{0.1}$MnO${}_3$ suggests the existence of a phase line separating the AFM-1 phase from the AFM-2 and AFM-3 phases, which is observed for $x$ $=$ 0.1. Magnetodielectric coupling was evidenced for both $x$ $=$ 0.1 and 0.2 compositions. Ferroelectric polarization and magnetodielectric coupling coefficient are larger for the latter composition.

• Received 31 May 2011

DOI:https://doi.org/10.1103/PhysRevB.84.094414