High-field magnetoelectric coupling and successive magnetic transitions in the Mn-doped polar antiferromagnet Ni3TeO6

Among the $3d$ transition metal ions doped polar Ni₃TeO₆, Mn-doped Ni₃TeO₆ has stimulated great interest due to its high magnetic ordering temperature and complex magnetic phases, but the mechanism of magnetoelectric (ME) coupling is far from understood. Herein we report our systematic investigation of the chemical control of magnetism, metamagnetic transition, and ME properties of Ni_3-xMnₓTeO₆ single crystals in high magnetic field (H) up to 52 T. We present a previously unreported weak ferromagnetic behavior appeared in the $ab$ plane below 9.5 K in addition to the incommensurate helical and commensurate collinear antiferromagnetic states. In the low-field region, a spin-flop-type metamagnetic transition without any hysteresis occurs at Hc1 for $H//c$, while another metamagnetic transition accompanied with a change in electric polarization is observed at Hc2 in the high-field region both for $H//c$ and $H//ab$ above 30 K, which can be attributed to the sudden rotation of magnetic moments at Ni2 sites. The ME measurements reveal that a first-order ME effect is observed in the low-T and low-H regions, while a second-order ME coupling term appears above 30 K in the magnetic field range of Hc1<H<Hc2 for $H//c$ and H<Hc2 for $H//ab$, both becoming significant with increasing temperature. Eventually, they are dominated by the second-order ME effect near the antiferromagnetic transition temperature. The present work demonstrates that Ni_3-xMnₓTeO₆ is an exotic magnetoelectric material compared with Ni₃TeO₆ and its derivatives, thereby providing insights to better understand the magnetism and ME coupling in Ni₃TeO₆ and its derivatives.