Multiferroicity in Ni doped MnWO$_{4}$*

In this work, we studied the multiferroic properties of Mn$_{1-x}$Ni$_{x}$WO$_{4}$ for $x$=0.05, 0.10, 0.15, 0.20 and 0.30 with ferroelectric, magnetic and heat capacity measurements. For $x$=0.05 and 0.10, the maximum polarization is 38 $\mu$C/m$^2$ and ferroelectric transition temperature ($T_c$) is 13.2 K which is 0.5 K higher than in parent compound. For other increasing values of $x$, the polarization decreases. For $x$=0.15, due to onset of AF4 collinear phase, the polarization becomes maximum and then decreases at lower temperature. A small polarization of 2.3 $\mu$C/m$^2$ is observed for $x$=0.20 with $T_c$ lowered at $\sim $9.5 K and the polarization is completely suppressed for $x$=0.30. Unlike in Co doped MnWO$_4$, neutron scattering reveals only two (AF2 and AF4) AF magnetic phases and the onset of the AF4 phase shifts to higher temperature with increasing value of $x$.