Phase diagram of the orthorhombic, lightly lutetium doped EuMnO 3 magnetoelectric system
Résumé
This paper reports on structural, magnetic, dielectric, thermodynamic, and magnetodielectric properties of Eu1−xLuxMnO3, 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 Eu3+ by smaller Lu3+ 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 EuMnO3 and Eu0.9Lu0.1MnO3 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.