No abstract

Articles you may be interested inEffect of magnetic domain structure on longitudinal and transverse magnetoelectric response of particulate magnetostrictive-piezoelectric composites Appl. Phys. Lett.Theory of low-frequency magnetoelectric effects in ferromagnetic-ferroelectric layered composites A method for the preparation of magnetostrictive-piezoelectric particulate composites with enhanced magnetoelectric effect was developed. The composites were synthesized in situ forming a shell of barium titanate around nanoparticles of cobalt ferrite, varying the composition of the cobalt ferrite magnetostrictive phase from 20 to 60 wt. %. Cobalt ferrite nanoparticles were obtained by coprecipitation and then added to the precursor gel of barium titanate, allowing the in situ formation of the composite and thereby restricting the contact of the ferrite particles during sintering. The samples were sintered at a temperature ranging from 1100 to 1250°C for 12 h, followed by a plating step to be electrically poled. Additional samples were prepared by conventional mechanical milling for comparison, starting from cobalt ferrite prepared either by coprecipitation or the sol-gel technique and commercial barium titanate. Samples of same compositions prepared by different methods and sintered under the same conditions showed different behavior. For example, the in situ synthesized sample showed a piezoelectric d 33 constant approximately six times larger and a magnetoelectric voltage coefficient approximately three times larger than the corresponding mechanically milled samples. The piezoelectric d 33 constant decreased with the content of ferrite, achieving the maximum value of 44.6 pC/ N for the in situ prepared sample with 20 wt. % of ferrite sintered at 1200°C. The highest magnetoelectric effect was present in the composition of 50 wt. % ferrite sintered at 1200°C, with a magnetoelectric coefficient of 1.48 mV/ cm Oe at room temperature.

The preparation and characterization of hcp and fcc Ni and Ni/NiO nanoparticles is reported. Ni and Ni/NiO nanoparticles were obtained starting from a precursor material prepared using a citric assisted Pechini-type method and, then, followed by a calcination of the precursor in air at either 400 or 600°C for different times. The precursor was analyzed using thermogravimetric and differential thermal methods (TGA-DTA), and the resulting nanoparticles were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and vibrational sample magnetometry. Nanoparticles showed a phase transformation for Ni from hcp to fcc and/or to fcc NiO structure as the calcination time increased. The influence of the phase transition and the formation of NiO on the magnetic properties of the samples are discussed.

An overview of the current state of art of the ultrasonic treatment technology applied to polymer melts is presented. The research and technological advancements of the ultrasonic treatment as applied to development of polymeric materials are discussed. An analysis of the technological progress shows that the mechanism of the effects of ultrasound on polymer melts is not fully understood at present. Such lack in fully understanding the mechanism could limit the use of this versatile technology in future applications. Based on the critical analysis of the research progress to date, some key issues for a deeper understanding of the chemical and physical effects of ultrasound on polymer

No abstract