Abstract
A flop of electric polarization from Pc to Pa is observed in MnTiO3 as a spin flop
transtion is triggered by a c-axis magnetic field, Hc=7 T. The critical magnetic field for Pa is significantly
reduced in Mn1−xNixTiO3 (x=0.33). Neutron diffraction measurements revealed similar
magnetic arrangements for the two compositions where the ordered spins couple antiferromagnetically
with their nearest intra- and inter-planar neighbors. In the x=0.33 system, the single ion
anisotropies of Mn2+ and Ni2+ compete and give rise to an additional spin reorientation transition
at TR. A magnetic field, Hc, aligns the spins along c for TR<T<TN. The rotation of the collinear
spins away from the c-axis for T<TR alters the magnetic point symmetry and gives rise to new ME
susceptibility tensor form. Such linear ME response provides satisfactory explanation for behavior
of field-induced electric polarization in both compositions. As the Ni content increases to x=0.5 and
0.68, the ME effect disappears as a new magnetic phase emerges.
