Fengzhen Huang

Effect of Nd dopant on magnetic and electric properties of BiFeO3 thin films prepared by metal organic deposition method

Polycrystalline Bi1−xNdxFeO3 (x=0–0.15) thin films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic deposition method. The effect of Nd dopant on the structural, electric, and magnetic properties was studied. It was found that the ferroelectric polarization and saturation magnetization of the films were enhanced by appropriate Nd doping due to the structural distortion and the suppressed cycloidal spin structure. Meanwhile, Nd-doped BiFeO3 thin films exhibited magnetic anisotropy because of the magnetocrystalline anisotropy.

Peculiar magnetism of BiFeO3 nanoparticles with size approaching the period of the spiral spin structure.

Size effect of multiferroics is important for its potential applications in new type miniaturized multifunctional devices and thus has been widely studied. However, is there special size effect in the materials with spiral modulated spin structure (such as BiFeO3)? It is still an issue to be investigated. In this report, structural, magnetic and magnetoelectric coupling properties are investigated for sol-gel prepared BiFeO3 nanoparticles with various sizes. It is found that a structural anomaly arises for the particles with size close to the 62 nm period of the spiral modulated spin structure, which induces an obviously increased ferromagnetism. In addition, large magnetoelectric coupling effect is observed in 62 nm BiFeO3 nanoparticles. Our result provides another insight into the size effect of BiFeO3, and also a clue to the magnetic structure at nanoscale.

Oxygen-vacancy-related high-temperature dielectric relaxation in SrTiO3 ceramics

Quantum paraelectric SrTiO3 has resulted in many investigations because of the anomalous properties. Here, using the conventional solid-state reaction method, we fabricated polycrystalline SrTiO3 ceramics with pure cubic perovskite structure. A dielectric loss peak is observed at around 450 K and 100 Hz and it shifts to higher temperature with increasing frequency. The typical high-temperature dielectric relaxation process is confirmed to be related to the oxygen vacancies (OVs) inside ceramics. More interestingly, a Cole–Cole fitting to loss peaks reveals a weaker correlation among OVs for such dielectric materials compared with that of ferroelectrics.

Study on dielectric and magnetodielectric properties of Lu3Fe5O12 ceramics

Polycrystalline Lu3Fe5O12 ceramics with garnet structure were prepared by a solid-state reaction method. A dielectric relaxor behavior at low temperature was observed which may come from the dipolar effects associated with the charge carrier hopping between Fe2+ and Fe3+. It is noticeable that their magnetodielectric (MD) properties are excellent since the applied small magnetic fields can dramatically change the dielectric constants of Lu3Fe5O12 ceramics. The origin of the MD effect is discussed.

Multiferroic properties and dielectric relaxation of BiFeO3∕Bi3.25La0.75Ti3O12 double-layered thin films

BiFeO3 (BFO)∕Bi3.25La0.75Ti3O12 (BLT) films were prepared on (111) Pt∕Ti∕SiO2∕Si substrates via metal organic decomposition method. The multiferroic and dielectric properties of the films were studied. It was found that the ferroelectric polarization and dielectric constant of the films were enhanced by introducing BLT as a barrier layer between BFO and Pt bottom electrode, while the ferromagnetism of BFO was not influenced. More interestingly, the films showed dielectric relaxor behavior, and the possible causes of which were discussed.

Study of multiferroic properties in Bi5Fe0.5Co0.5Ti3O15 thin films

To explore the novel thin film with multiferroicity at room temperature, the bismuth-layer-structured Bi5Fe0.5Co0.5Ti3O15 (BFCT) thin films were prepared using chemical solution deposition technique. The microstructure, electric, and magnetic properties were investigated in BFCT film. A defined hysteresis loop of the BFCT film was obtained with the remnant polarization (2Pr) ∼ 31.7 μC/cm2 at 1 kHz under the electric field 300 kV/cm. To exclude contribution of the leakage current to polarization, we studied the dependence of hysteresis loops on the measuring frequency in the range from 100 Hz to 2 kHz and made the positive-up-negative-down (PUND) measurements in BFCT thin film. Both the results indicate the intrinsic ferroelectric property, and the leakage current does not play a big role in BFCT film. Meanwhile, the ɛ-V curve can also support the natural ferroelectricity in the BFCT film. We also found that the BFCT film shows weak ferromagnetism with the saturated magnetization (Ms) ∼2.6 emu/cm3. Further...

The effect of Fe2+ ions on dielectric and magnetic properties of Yb3Fe5O12 ceramics

Yb3Fe5O12 ceramics with garnet structure were prepared employing the solid-state reaction method. The results reveal that the emergence of Fe2+ ions greatly affects dielectric relaxation, magnetic relaxation, saturation magnetization, and magnetoelectric coupling, which was further confirmed by oxygen treatment. More interestingly, the magnetoelectric coefficient (α) reaches 28 ps m−1 at room temperature, which is among the largest values for present single-phase magnetoelectric materials.

Multiferroic behaviour and the magneto-dielectric effect in Bi5FeTi3O15 thin films

Thin films of Fe-containing the Aurivillius phase Bi5FeTi3O15 (BFTO) were successfully prepared by chemical solution deposition. The microstructure, ferroelectric behaviours, magnetic properties and the magneto-dielectric effect were investigated systematically at room temperature (RT). A definite hysteresis loop of the BFTO film was obtained with the remanent polarization (2Pr)???43.3??C?cm?2 under an electric field of 300?kV?cm?1. To exclude the contribution of the leakage current to polarization, we studied the frequency dependence of hysteresis loops in the BFTO thin film and made positive-up?negative-down measurements. These results indicated the intrinsic ferroelectricity in the present BFTO film and it was supported by the ??V curve. Furthermore, a weak ferromagnetism with an in-plane saturated magnetization (Ms) of ??1.7?emu?cm?3 was also observed in the BFTO film, which may have originated from the Fe2+?O?Fe3+ nanocluster and the F-centre exchange (FCE) mechanism. Therefore, the ferromagnetism could be considered as in nanoregions. More importantly, the magneto-dielectric effect was found with a magneto-dielectric coefficient of ??2.8% at a frequency of 100?kHz at RT. The probable origins of magnetic anisotropy and the magneto-dielectric effect were discussed. All these results demonstrated the RT multiferroic behaviour of the BFTO film.

Critical radii of ferroelectric domains for different decay processes in LiNbO3 crystals

The LiNbO3 crystals were polarized at fixed points and characterized by means of scanning probe microscope. The growth evolution and the decay process of the fabricated domains were carefully studied. Two critical radii rC and Rc that determine a different decay behavior of domains were put forward, where rC is considered to correspond to the point when the domains just penetrate the crystal. Those domains with radius larger than rC could exist beyond 5days, those between rC and Rc experienced a distinct metastable state before completely disappearing, while those smaller than Rc were even invisible under piezoresponse force mode.

Tunable electric properties of PbZrO3 films related to the coexistence of ferroelectricity and antiferroelectricity at room temperature

Polycrystalline PbZrO3 films with a preferred orientation were fabricated via the metal-organic decomposition method. For heat-treated PbZrO3 films, the P-E hysteresis loops, dielectric spectra, and I-V curves show interesting changes with time, which strongly suggest the coexistence of antiferroelectric and ferroelectric phases at room temperature. Based on the easy transition between these two phases, the electric properties of the films become tunable. A dielectric tunability of about 50.2% below 8.2 V makes it a promising low working-voltage dielectric tunable material, and the significant current change of four orders of magnitude indicates potential application as a voltage-controlled rheostat.