Effect of nonmagnetic substituents Mg and Zn on the phase competition in the multiferroic antiferromagnet MnWO4

TL;DR

This study investigates how substituting nonmagnetic Mg and Zn ions into MnWO4 affects its structural, magnetic, and ferroelectric properties, revealing similar effects on phase transition temperatures and magnetic structures.

Contribution

It provides new insights into how Mg and Zn doping influence phase competition and magnetic structures in multiferroic MnWO4.

Findings

Both Mg and Zn doping reduce the Neel and ferroelectric transition temperatures.

Similar magnetic structures are observed at certain doping levels, indicating comparable effects of Mg and Zn.

Doping induces incommensurate magnetic phases similar to the undoped material.

Abstract

The effects of substituting nonmagnetic Mg2+ and Zn2+ ions for the Mn2+ (S = 5/2) ions on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet MnWO4 were investigated. Polycrystalline samples of Mn1-xMgxWO4 and Mn1-xZnxWO4 (0<x<0.3) solid solutions were prepared by a solid-state route and characterized via X-ray and neutron diffraction, magnetization, and dielectric permittivity measurements. Mg and Zn substitutions give rise to very similar effects. The Neel temperature TN, the AF3-to-AF2 magnetic phase transition temperature T2, and the critical ferroelectric temperature Tc = T2 of MnWO4 are reduced upon the 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.