Thermodynamics and multiferroicity in PbTiO3 due to 4/5d electrons doping

Coexistence of ferromagnetism (FM) and spontaneous ferroelectric polarization (SP) is of great interest from both a fundamental and technological applications point of view in spintronic and high-density data storage devices. Here, we systematically investigated the possibility of FM and SP together in the PbTi87.5X12.5O3 (X = Zr, Nb, Mo, Hf, Ta, and W) systems by means of density functional theory calculations. Energetic stability of the doped systems is analyzed under appropriate thermodynamic conditions. We found that doped systems can be formed spontaneously at 0 K under Ti-poor and oxygen-poor/rich conditions. All the doped systems exhibit metallicity with a reasonable charge carrier density (similar to 10(21) cm(-3)) and SP magnitude, except Zr and Hf due to the same valence as that of Ti. The microscopic origin of the conductivity in these doped structures is the charge distribution of extra electrons provided by Nb, Mo, Ta, and W dopants when doped at the Ti site. Interestingly, our calculations reveal that Mo and W doped PbTiO3 (PTO) systems show magnetism, which, further, strongly react with the on-site Coulomb repulsion (U), and the W@Ti doped system becomes half-metallic (one channel is a conductor and other is an insulator) FM. Moreover, the Ta-doped PTO system also shows a propensity to magnetism with the implementation of U. It is our belief that these findings open a new simple route to achieve multiferroics in perovskites and other related ferroelectric materials via 4/5d dopants.