Enhanced multiferroic properties of Bi4Ti3-xCoxO12/La0.67Sr0.33MnO3 layered composite thin films

In this work, Bi₄Ti_3-xCo_xO₁₂/La_0.67Sr_0.33MnO₃ (BITC_x/LSMO, x = 0.025, 0.05, 0.10 and 0.15) layered magnetoelectric (ME) composite thin films were successfully synthesized by chemical solution deposition, and the effect of Co²⁺ doping content on the microstructure, leakage, dielectric property, ferroelectricity, ferromagnetism and ME coupling performance of BITC_x/LSMO composite thin films was investigated. Co²⁺ doping induces improved ferroelectricity and weak ferromagnetism for the BITC_x phase. Especially, the single-phase BITC_0.05 film exhibits a maximum ME voltage coefficient (α_E) of 0.445 mV/cm·Oe at room temperature, suggesting excellent single-phase multiferroic properties. The BITC_0.05/LSMO composite thin film possesses the lowest leakage current density, maximum ?_r, minimum tanδ, highest remnant polarization of 24.2 μC/cm², lowest coercive field of 137 kV/cm and improved saturation magnetization along with a maximum a_E value of 27.3 V/cm·Oe. Based on these findings, Co²⁺-doped Bi₄Ti₃O₁₂ has excellent single-phase multiferroic properties, and the incorporation of magnetic ion-doped Bi₄Ti₃O₁₂ with ferromagnetic oxides benefits the improvement of ME composite thin films.     

Elastically stressed state at the interface in the layered ferromagnetic / ferroelectric structures with magnetoelectric effect

This article shows that in layered structures representing thin (～2 μm) cobalt, nickel and permendur layers on ferroelectric ceramics substrates (～400 μm) the elastic strains at the interface make a more significant contribution to the magnetoelectric effect than the ferromagnetic layer magnetostriction. For obtaining these structures the ion-beam sputtering – deposition after ion-beam planarization of the substrate surface was used. The magnetoelectric voltage coefficient at a frequency of an alternating magnetic field of 1 kHz at room temperature for structures with cobalt is higher than that for structures with nickel and permendur. The structures obtained are thermostable within the temperature range from ?25 to +120 °C and have reproducible magnetoelectric properties. These structures can find their application as magnetoelectric converters and magnetic fields sensors.     

Defect-Enhanced Polarization Switching in the Improper Ferroelectric LuFeO3

Results of switching behavior of the improper ferroelectric LuFeO₃ are presented. Using a model set of films prepared under controlled chemical and growth-rate conditions, it is shown that defects can reduce the quasi-static switching voltage by up to 40% in qualitative agreement with first-principles calculations. Switching studies show that the coercive field has a stronger frequency dispersion for the improper ferroelectrics compared to a proper ferroelectric such as PbTiO₃. It is concluded that the primary structural order parameter controls the switching dynamics of such improper ferroelectrics.     

Negative zero-field-cooled magnetization and magnetic switching in multiferroic Lu0.5Sc0.5FeO3 ceramics

In this study, we have investigated the negative magnetization of Lu_0.5Sc_0.5FeO₃ (LSFO) ceramics in the zero-field-cooled (ZFC) mode. The negative magnetization in ZFC measurement appears below the Neél temperature (T_N) in LSFO, which is probably caused by the residual negative trapping field in superconducting magnet, and is closely related to the giant coercivity in LSFO. By fitting the high-temperature paramagnetic data under nominal zero magnetic field, the negative trapping field in superconducting magnet is found to be −3.28 Oe. The giant coercivity is ascribed to the strong uniaxial magnetocrystalline anisotropy in LSFO, which can cause the strong magnetic domain wall pinning effect to limit the nucleation of reversed domains under reverse field. In addition, a switchable magnetization switching is realized in LSFO. The magnetization of LSFO can stably switch between positive and negative values when the applied magnetic field was switched between 0.5 and 3 kOe, which suggests that the LSFO samples are suitable for potential applications in magnetic storage.     

Dielectric anomalies in orthorhombic YMnO3 thin films

We report on the magnetodielectric characterization of orthorhombic (001) oriented YMnO₃ thin films grown by PLD on Nb-doped SrTiO₃. Detailed temperature, magnetic field and frequency dependent measurements are used to determine dielectric and magnetodielectric response and to analyse its origin. A dielectric peak below the Néel temperature is observed. We show that this peak signals a magnetoelectric coupling as inferred from a magnetocapacitance of about 2% at 8 T and 25 K. A careful analysis of the impedance spectroscopy allows concluding that both the dielectric peak and the measured magnetocapacitance are intrinsic properties of YMnO₃. At higher temperatures (> 200 K) another dielectric feature (a strong frequency dependency and a peak in the dielectric losses) is observed, which is ascribed to the Maxwell-Wagner behaviour and thus it is not a genuine response of stoichiometric YMnO₃.     

铁电性SBT和铁磁性NiCuZn铁氧体复合材料的制备

采用固相法成功制备了铁电性SBT和铁磁性NiCuZn铁氧体的复合材料。借助于TMA，XRD和SEM技术，对复合材料的共烧特性、物相组成以及显微结构进行了研究。共烧特性研究表明，SBT和NiCuZn铁氧体的烧成收缩和烧成收缩率存在差异。物相分析表明，复合体系均由NiCuZn铁氧体和SBT两相所组成。显微结构表明，复合材料具有较高的密度和良好的显微结构。NiCuZn铁氧体的平均晶粒尺寸比SBT要大。     

新型铁磁电薄膜的研究现状

本文综述了各种结构的多铁薄膜的性能及研究过程中需要解决的问题。     

In situ sol-gel co-synthesis at as low hydrolysis rate and microwave sintering of PZT/Fe2CoO4 magnetoelectric composite ceramics

Pb(Zr_0.53Ti_0.47)O₃/Fe₂CoO₄ (PZT/Fe₂CoO₄) diphase particulate composites were prepared in an 80:20 M ratio by the in situ sol-gel co-synthesis method. Controlling the hydrolysis rate of the metal-organic reagents used in the formation of the sol was essential to obtain a nanostructured system with a highly homogeneous and immiscible two-phase distribution. The compact diphase powders were densified throughout the microwave-assisted sintering methods for controlling grain growth, and to evaluate this new nanostructure and effect on the physical properties of this material. The characterizations revealed that the new in situ sol-gel co-synthesis method was successful in producing highly homogeneous nanopowders without secondary phases. The powders processed at low hydrolysis rates showed the formation of a core-shell particle architecture. After microwave-assisted sintering, the samples showed uniform distribution of the cobalt ferrite phase in the PZT phase, with an average nanograin size of about 300 nm, while the same material sintered conventionally had an average cobalt ferrite grain size of about 6 µm. Innovative PZT/Fe₂CoO₄ nanostructures were obtained with magnetoelectric response.