Giant Magnetoelectric Coupling in Multiferroic PbTi_1- V O₃ from Density Functional Calculations

Giant magnetoelectric coupling is a very rare phenomenon that has gained much attention in the past few decades due to fundamental interest as well as practical applications. Here, we have successfully achieved giant magnetoelectric coupling in PbTi_1- V O₃ (x = 0-1) using a series of generalized gradient-corrected GGA (generalized gradient approximation), including on-site Coulomb repulsion (U)-corrected spin-polarized calculations based on accurate density functional theory. Our total energy calculations show that PbTi_1- V O₃ stabilizes in C-type antiferromagnetic ground state for x > 0.123. With the substitution of V into PbTiO₃, the tetragonal distortion is highly enhanced accompanied by a linear increase in polarization. In addition, our band structure analysis shows that for lower x values, the tendency to form two-dimensional magnetism of PbTi_1- V O₃ decreases. The orbital magnetic polarization was calculated with self-consistent field method by including orbital polarization correction in the calculation as well as from the computed X-ray magnetic dichroism spectra. A nonmagnetic metallic ground state is observed for the paraelectric phase for V concentration (x) = 1 competing with a volume change of 10% showing a large magnetovolume effect. Our orbital-projected density of states as well as orbital ordering analysis suggest that the orbital ordering plays a major role in the magnetic-to-nonmagnetic transition when going from ferroelectric to paraelectric phase. The calculated magnetic anisotropic energy shows that the direction [110] is the easy axis of magnetization for x = 1 composition. The partial polarization analysis shows that the Ti/V-O hybridization majorly contributes to the total electrical polarization. The present study adds a new series of compounds to the magnetoelectric family with rarely existing giant coupling between electric- and magnetic-order parameters. These results show that such kind of materials can be used for novel practical applications where one can change the magnetic properties drastically (magnetic to nonmagnetic, as shown here) with external electric field and vice versa.