  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
Ni3-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
Ni3-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.
