Structure, electrical and magnetic property investigations on dense Fe-doped hexagonal BaTiO3

Abstract

Hexagonal Ba(Ti 1Àx Fe x )O 3Àd (x ¼ 1/6, 1/3) ceramics treated with post annealing are specifically synthesized to explore the origin mechanism of the unusual ferromagnetism in the doped system. X-ray diffraction refinements and transmission electron microscope experiments reveal that their structures are incommensurately modulated owing to simultaneous oxygen vacancies at both O1 and O2 sites. Consequently, coexisting weak ferrielectricity and weak ferromagnetism are presented at room temperature. Analysis on their leakage current plot reveals that their conduction follows trap-filled limit model. In combination with the magnetism studies on 5 mol% Fe-doped crystals [Phys. Rev. B 83, 144407 (2011)], the reduction of ferromagnetism with an increase of conductivity suggests that dynamic exchanges of trapped electrons among the bound magnetic polarons attribute to the intrinsic ferromagnetism.

Room-Temperature Ferromagnetism in Nickel-Doped Wide Band Gap Ferroelectric Bi_0.5K_0.5TiO₃ Nanocrystals

“…This phenomenon is well known in transition metal-doped wide band gap ferroelectric materials such as Fe-doped Bi 0.5 Na 0.5 TiO 3 or PbTiO 3 , etc., which results from the contribution of paramagnetic isolated magnetic ion. 9,10,15,16) Thus, the observed magnetism in Ni-doped Bi 0.5 K 0.5 TiO 3 samples is attributed to the competition between ferromagnetism and paramagnetism. For higher Ni-doped Bi 0.5 K 0.5 TiO 3 samples, e.g.…”

“…The diffraction peak shifted due to transition metal presence at Ti-site and different ionic radii between them. 9,10,16,17) Note that the ionic radius of Ni depends on the coordination number charge and spin states, etc. The ionic radii of Ni 2+ , Ni 3+ , Ni 4+ and Ti 4+ with six coordination are 0.069, 0.056, 0.048, and 0.061 nm, respectively.…”

“…There are four ways to obtain and to develop the multiferroic materials: i) enhancing the performances of natural multiferroic materials such as BiFeO 3 , 5) ii) synthesis of new multiferroic materials such as KBiFe 2 O 5 , 6) iii) combining ferromagnetic materials with ferroelectric materials as composite or multilayer such as BaTiO 3 -CoFe 2 O 4 or NiFe/ BiFeO 3 , etc., 7,8) and iv) introducing the transition metal to ferroelectric material as dopants such as Fe-doped BaTiO 3 . 9) Recently, the ferromagnetism at room temperature was obtained in transition metal Mn-and Fe-doped PbTiO 3 and PbTiO 3 -CoFe 2 O 4 composite, 1012) However, since Pb in leadbased material pollutes environment and harmful to human, considerable effort has been devoted towards the development of lead-free multiferroic materials. 13) Among lead-free ferroelectric materials, the Bi 0.5 A 0.5 TiO 3 (A = Na, K) are widely studied.…”

Structural incommensurate modulation rule in hexagonal Ba(Ti1-xMx)O3-δ (M = Mn, Fe) multiferroics

“…Investigations such as X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and Mössbauer spectra have revealed that oxygen vacancies (Vos) prefer to occupy the O1 site and partial Ti 4+ ions will be reduced into Ti 3+ ions in the hexagonal matrix. [9][10][11][12][13][14] The conductivity almost increases linearly with the increase of the oxygen vacancy content since more compensated electrons are introduced at the same time. However, positive contribution of more vacancy to FM only works as the doping content of Fe is less than 12 mol%, 11,15 further doping would weaken the ferromagnetic interaction.…”

“…Such a behavior can mainly be ascribed to the crystal and electronic structure changes because of doping, e.g., occupancy ratio change of the dopants at Ti1 and Ti2 sites, the coordination number change of the transition metals and the introduction of defect structures. 10,16 a Author to whom correspondence should be addressed: Electronic mail: rcyu@aphy.iphy.ac.cn. Our previous study on dense Fe-doped hexagonal BaTiO 3 reported the multiferroic behavior of the incommensurately modulated system.…”