Large tunability of the magnetoelectric effect in the Co-substituted polar antiferromagnet Ni3TeO6

Polar magnet Ni3TeO6 has been recently attracting considerable interest due to its nonhysteretic magneto-electricity associated with the collinear antiferromagnetic (AFM) order. Nevertheless, the magnetoelectric (ME) response in Ni3TeO6 remains trivial, and especially lacks sufficient tunability. Herein, we report large tunability of the ME effect in Co-substituted Ni3TeO6, and special attention is paid to Ni2CoTeO6 and NiCo2TeO6 single crystals where incommensurate AFM helical structure with spins lying in the ab plane is established, distinctly different from the collinear AFM structure in Ni3TeO6 along the c axis. Our results demonstrate that the Co2+ substitution results in emergence of a giant electric polarization Pc up to & SIM; 0.52 & mu;C/cm2 induced by a magnetic field normal to the c axis, i.e., the polar axis. The generated Pc in NiCo2TeO6 is approximately 8.45 and 1.8 times larger than that of Ni2CoTeO6 and Ni3TeO6, respectively. More importantly, the linear ME coefficient & alpha; can be remarkably modulated by the Co2+ substitution, evidenced with a large & alpha; & SIM; 323 ps/m for NiCo2TeO6, a small & alpha; & SIM; 3.4 ps/m for Ni2CoTeO6, and an intermediate & alpha; & SIM; 36 ps/m for Ni3TeO6 at temperature T & SIM; 45 K. Such remarkable Co-substitution control of the ME effect is believed to be associated with the different occupations of the Ni/Co ions at the specific lattice sites. This work thus provides insights into the high-tunability ME effect in Ni3TeO6 polar magnets, a largely unexplored topic.