Modulated multiferroic phases and electric polarization in Mn1−xRuxWO4+δ

In this work, we investigate the multiferroic phase stability against 4d Ru substitution of 3d Mn in Mn1−xRuxWO4+δ. The Ru substitution results in both Ru3+ and Ru4+ occupations at the Mn sites, while oxygen interstitials in the lattice are expected owing to the charge neutrality requirement. It is suggested that the local electric dipoles as induced by the charge valence variations of Ru cancel with each others, making no contribution to the ferroelectric polarization. The Ru-substitution induced lattice distortion and chemical disorder may be responsible for the enhanced stability of the ferroelectric AF2 phase over the non-ferroelectric AF1 phase, thus leading to the observed polarization enhancement.