Distinctive effects of dopant valency is discussed using an impurity level 1% doping each of Cr$^{ 3+}$ and Ni$^{ 2+}$ in CaBaCo$_4$O$_7$. Through a comparative study of the magnetic and dielectric properties of multiferroic CaBaCo$_{ 3.96}$Cr$_{ 0.04}$O$_7$ and CaBaCo$_{ 3.96}$Ni$_{ 0.04}$O$_7$, we highlight that Cr doping does not significantly alter the properties in spite of differences in magnetic spin and ionic radius compared to Co$^{ 3+}$ and Co$^{ 2+}$ while Ni doping induces spectacular changes. Particularly, a manifold increase of electric polarization change up to 650 ${ \rm \mu}$C/m$^2$ at 5.6 kV/cm is observed in CaBaCo$_{ 3.96}$Ni$_{ 0.04}$O$_7$ compared to CaBaCo$_{ 3.96}$Cr$_{ 0.04}$O$_7$ and a stronger magnetoelectric coupling leading to a polarization change of $\sim$ 12% in 15 T magnetic field and below 40 K. Further, magnetodielectric effects hint to competing magnetic phases over the temperature range of magnetic transitions. We discuss the observed disparity in the light of a possible site selective doping of Cr$^{ 3+}$ and Ni$^{ 2+}$ in the triangular and kagom\'e layers, respectively, of the parent compound.
Categories: cond-mat.str-el cond-mat.mtrl-sci