Magnetoelectric coupling tuned by competing anisotropies in Mn₁₋ₓNiₓTiO₃

الأصل · EN

A flop of electric polarization from P (Pc) to P (Pₐ) is observed in MnTiO₃ as a spin flop transition is triggered by a c-axis magnetic field, Hc=7 T. The critical magnetic field Hc for Pₐ is significantly reduced in Mn₁₋ₓNiₓTiO₃ (x=0.33). Pₐ and Pc have been observed with both Hc and Hₐ. 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 uniaxial and planar anisotropies of Mn²⁺ and Ni²⁺ compete and give rise to a 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 a new ME susceptibility tensor form. Such linear ME response provides satisfactory explanation for the behavior of the 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.