Bandgap modulation and magnetic switching in PbTiO3 ferroelectrics by transition elements doping

Transition metal (TM=Fe, Ni and Mn) ions doped PbTiO3 perovskite ferroelectric ceramics prepared by a solid state reaction method have been studied by means of structural characterizations, optical and magnetic measurements. All the samples have pure tetragonal perovskite structure, but exhibit different grain shapes and sizes with the introduction of TM ions and oxygen vacancies. The observed structural changes arise from internal lattice strain, which is estimated by Williamson-Hall (W-H) analysis model. Moreover, TM ions doping plays simultaneously an important role on the energy band structure and magnetic orderings. The energy gap of PbTi0.95TM0.05O3−δ shows a drastic decrease compared to that of PbTiO3. Furthermore, PbTi0.95TM0.05O3-δ materials possess multiple magnetism switching, in which diamagnetic-ferromagnetic transition and ferromagnetic-paramagnetic transition occur. In particular, the Fe-doped PbTiO3 ceramic presents a typical ferromagnetic hysteresis, originating from the effective exchange coupling interaction between oxygen vacancies and Fe 3d spins.