Effect of Nonmagnetic Substituents Mg and Zn on the Phase Competition in the Multiferroic Antiferromagnet MnWO₄

International audienceThe effects of substituting nonmagnetic Mg2þ and Zn2þ ions for the Mn2þ (S=5/2) ions on the structural, magnetic, and dielectric properties of the multiferroic frustrated antiferromagnetMnWO4 were investigated. Polycrystalline samples ofMn1-xMgxWO4 andMn1-xZnxWO4 (0exe0.3) solid solutions were prepared via a solid-state route and characterized via X-ray and neutron diffraction, magnetization, and dielectric permittivity measurements. Mg and Zn substitutions result in very similar effects. The N eel temperature (TN), the AF3-to-AF2 magnetic phase-transition temperature (T2), and the critical ferroelectric temperature (Tc=T2) of MnWO4 are reduced upon nonmagnetic doping. At the lowest temperature (T=1.5 K), the incommensurate magnetic structure for x(Mg)=0.15 and x(Zn)=0.15 corresponds to either a sinusoidal spin arrangement or an elliptical spin-spiral phase similar to the polar AF2 structure observed in MnWO4. These findings were discussed by considering the effects of the Mg and Zn substitutions on the crystal lattice and on the spin exchange network of MnWO4