Xiangyu Mao

Multiferroic properties of layer-structured Bi5Fe0.5Co0.5Ti3O15 ceramics

Layer-structured, single phase Bi5Fe0.5Co0.5Ti3O15 ceramics was synthesized following a multicalcination procedure. Magnetic moment increases more than three times by substituting half Fe sites by Co ions. The material exhibits an Aurivillius phase with a four-layer unit cell structure, and presents a remarkable coexistence of ferroelectricity and ferromagnetism above room temperature. The measured 2Pr and 2Mr are 13 μC/cm2 and 7.8 memu/g, respectively. The material’s magnetic behavior below 275 °C is relaxationlike and its magnetic Curie temperature is ∼345 °C.

Ferromagnetic, ferroelectric properties, and magneto-dielectric effect of Bi4.25La0.75Fe0.5Co0.5Ti3O15 ceramics

Multiferroic properties of four-layered Bi4.25La0.75Fe0.5Co0.5Ti3O15 ceramics were carefully investigated. X-ray diffraction and high resolution transmission electron microscopy analyses indicate that the as-prepared sample is almost free from secondary phases, and magnetization measurements confirm a ferromagnetic transition ∼483 K. At room temperature (RT), the sample shows a typical ferromagnetism with a remnant magnetization (2Mr) of ∼51.2 m emu/g, and a good ferroelectric hysteresis with a remnant polarization (2Pr) of ∼15.4 μC/cm2. More importantly, an obvious magneto-dielectric (MD) effect has been found under a low magnetic field of 1 T at RT with a maximum of magneto-dielectric constant of ∼10.5%.

Synthesis of Ni-substituted Bi7Fe3Ti3O21 ceramics and their superior room temperature multiferroic properties

Layer-structured bismuth complex oxides Bi7Fe3−xNixTi3O21 (0 ≤ x ≤ 2) (BFNT) were synthesized using a low-temperature combustion synthesis method. X-ray diffraction patterns and high-resolution transmission electron microscopy analysis indicated that the samples presented a six-layer Aurivillius structure. Substituting Fe sites by Ni ions inside the lattice was found to be effective in enhancing the multiferroic properties at or above the room-temperature. The sample with a composition of x = 1 exhibited a large remnant magnetization (2Mr = 1.32 emu g−1) that is about five hundred times higher than that in un-substituted Bi7Fe3Ti3O21 ceramics. The work is an important step in the effort to find a single phase and a fully functioning multiferroic material.

Self-modulated nanostructures in super-large-period Bi11(Fe5CoTi3)10/9O33 epitaxial thin films

Super-large-period Aurivillius thin films with a pseudo-period of ten were grown on (0 0 1) SrTiO3 substrates using the pulsed laser deposition method. The as-grown films are found to be coherently strained to the substrate and atomically smooth. X-ray diffraction indicates an average periodicity of ten, while analysis with the high resolution scanning transmission electron microscopy reveals a self-modulated nanostructure in which the periodicity changes as the film thickness increases. Finally, we discuss the magnetic and possible ferroelectric properties of the self-modulated large period Aurivillius films at the room temperature.

Room-temperature multiferroic responses arising from 1D phase modulation in correlated Aurivillius-type layer structures

Structural instability induced by chemical substitution in multiferroic materials, especially in layer-structured oxides of the Bi4Ti3O12–BiFeO3 system, gives rise to intriguing phenomena and extraordinary coupling properties. In this work, we carefully studied an analogous morphotropic structural transformation in Co-substituted Bi7Ti3Fe3O21 oxides, similar to a morphotropic phase boundary. Large effects (including ferroelectric, dielectric and ferromagnetic) and abnormal magnetic behaviour were recorded at the analogous morphotropic transformation region (AMTR). 1D phase-modulated structures composed of two different layered phases and structural distortions inside the AMTR were visualized. Analyses of the correlations between oxygen octahedral distortions and multiferroic responses confirmed that the enhanced multiferroic responses inside the AMTR are intrinsic to the 1D correlated interface structures, mainly arising from such structural distortions due to the existence of different lattice strains and the change of crystal symmetry.

Multiferroic Behavior and Orientation Dependence of Bi5Fe0.5Co0.5Ti3O15Thin Film

Bismuth-based layer-structured Bi5Fe0.5Co0.5Ti3O15(BFCT) thin films have been deposited on Pt/Ti/SiO2/Si substrates by chemical solution deposition method. Using different heating rates during crystallization, we obtained randomly oriented and highly c-axis-oriented BFCT films. Anisotropic ferroelectricity were determined with the remnant polarization (2P r) ∼ 45.8 μC/cm2 for randomly oriented film and 2P r∼ 25.3 μC/cm2 for highly c-axis-oriented ones. Meanwhile, highly c-axis-oriented BFCT film shows better fatigue endurance than that of random orientation. Both above can confirm the ferroelectric anisotropy. Furthermore, magnetic anisotropy also has been observed and possible reasons were discussed.

Structural, Magnetic and Ferroelectric Properties of Bi5FeTi3O15 and Bi5Fe0.5Co0.5Ti3O15 Ceramics

The compounds Bi5FeTi3O15 (BFTO) and Bi5Fe0.5Co0.5Ti3O15 (BFCT) were prepared by incorporating BiFeO3(BFO) and BiFe0.5Co0.5O3 (BFCO) into the host Bi4Ti3O12 using the solid state reaction technique. The X-ray diffraction and Raman shift data indicate that the as-prepared materials are of the four-layer Aurivillius phases. At room temperature, the half substitution of Fe-O layer by Co-O layer is found to result in the increase in the 2P r by about 35% and simultaneously the decrease in 2E c by about 41%, respectively. The magnetic moment at least tripled its value by substituting half Fe ions by Co ions. The remnant magnetization (2M r) and the coercive field (2H c) were about 7.8 memu/g and 410 Oe, respectively.