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Introduction: Magnetoelectric (ME) materials become magnetized when placed in an electric field and electrically polarized when placed in a magnetic field. Thus an effective conversion between electric and magnetic energy becomes possible, and ME materials present themselves as one kind of smart materials. They can be classified into two classes: single phase and composite. For single phase materials, due to the primary requirement to observe the ME effect is the coexistence of magnetic and electric dipoles in an asymmetric structure, the number of compounds that exhibit ME effect is limited, the ME coefficient, α E = (∂E/∂H) T , is small, working temperature is low and involved expensive materials and processing techniques. These limitations can be overcome when shifted to composites, which usually consist of magnetostrictive and piezoelectric phases, resulting in a ME effect as product property of this combination [1]. Experimental: Samples were synthesized using wet chemical method. CoFe 2 O 4 powder obtained from appropriate solution by coprecipitation was introduced as core to the solution of acetic acid, barium hydroxide and titanium(IV) n-Butoxide which is then gelated on the surface of the CoFe 2 O 4 core during heating and stirring. The gels were dried, presintered and pressed into pellets followed by a heat treatment and electrically poling procedure, then painted by silver paste for electric contacts. Crystalline structures of the composites were investigated by X-ray diffractometer (XRD). Magnetic properties were studied using a pulse field magnetometer. Magnetostriction was measured using strain gauge method. AC susceptibility and ME coefficient were investigated using lockin technique in which AC fields with frequencies from 1Hz to 4kHz and amplitudes from 0,1Oe to 20Oe superimposed onto a DC magnetic field up to 6500 Oe were employed. Input resistance and capacitance of the lock-in are 100MΩ and 25pF. All measurements were carried out at room temperature and ambient pressure. Discussions: The XRD patterns suggested that the composites consist two single phases: CoFe 2 O 4 and BaTiO 3 . The saturation magnetization and coercivity of the CoFe 2 O 4 component in the composite are 78emu/g and 460Oe, which are similar to those of the bulk sample. ME coefficient α E was determined using the equation α E =V/(d.H AC ) where V is output voltage of the lock-in, d is the thickness of the sample and H AC is the amplitude of the AC field. ME coefficient-Bias field curves, α E -H DC , has a hysteretic nature, and a remanence is also observed. Under an AC field of 10Oe with frequency of 270Hz, the maximum longitudinal and transversal α E are 1,58mV/Oe.cm and 0,95mV/Oe.cm, see Fig.1. These α E are about 20 times higher as compared to those of the reference sample which is produced by mixing the two powders, suggesting that the coupling between the two phases in the core-shell structure is much better than those in the mixture. In the mixed structure, the longitudinal ME coefficient is smaller than the transversal ...

The hybrid nanoparticles Ag-MnFe 2 O 4 was successfully fabricated by the seed-growth method and thermal decomposition method. The shape and size of these nanoparticles were evaluated by Transmission electron microscopes (TEM) images showing that these nanoparticles are quite uniform and have a diameter of about 20 nm. The UV-Vis spectrum of hybrid nanoparticles Ag-MnFe 2 O 4 shows that in the wavelength region from 300 to 800 nm, the ferrite manganese nanoparticle does not appear to have an absorption peak, while the spectrum of the silver nanoparticle shows a characteristic surface plasmon resonance (LSPR) peak with peaks between 400 and 420 nm. Research results show that the hybrid nanoparticles Ag-MnFe 2 O 4 coated with PMAO (MFA10-PMAO) has the ability to inhibit both Escherichia coli bacteria-intestinal bacilli and Staphylococcus aureus bacteria. In which, the antibacterial ability with E. coli is stronger than that of S. aureus, the antibacterial zone diameter in both cases are 21.5 and 16 mm, respectively. In addition, MFA10-PMAO nanoparticles also showed easy recovery after treatment, which is favorable for reuse.

Các màng mỏng đa lớp [Co/Pd] có cấu trúc antidots phún xạ trên các đế xốp nano Al2O3 và TiO2 với kích thước lỗ xốp 30 nm và 50 nm được chế tạo bằng phương pháp phún xạ DC magnetron. Ảnh hưởng của hình thái bề mặt lên đặc trưng cấu trúc và tính chất từ trong các màng đa lớp đã chế tạo được khảo sát một cách kỹ lưỡng. Kết quả nghiên cứu chỉ ra rằng, tương tự như trong các màng phẳng [Co/Pd], các màng xốp cũng có dị hướng từ vuông góc lớn ở nhiệt độ phòng. Tuy nhiên, lực kháng từ HC trong các màng xốp có sự tăng cường đáng kể so với các màng phẳng, HC lớn nhất đạt được là 2220 Oe với mẫu màng xốp TiO2-[Co/Pd], lần lượt cao gấp 1,28 và 3,15 lần so với màng Al2O3-[Co/Pd] và màng phẳng SiO2-[Co/Pd], là do sự hình thành pha từ mềm tại gờ các lỗ xốp. Có thể nói tính chất từ trong các màng xốp hoàn toàn có thể được điều biến thông qua việc điều chỉnh các thông số cấu trúc của đế xốp như kích thước lỗ xốp và độ nhám bề mặt.