A technique to solubilize fine magnetic inorganic particles in general organic solvents is proposed via surfaces modification by long-chain carboxylic acids. This organic modification should overcome the relatively weak van der Waals interactions between the nanoparticles, allowing the formation of ordered arrangements of the modified Fe3O4 and CoFe2O4 materials. Using nanodispersions of these organo-modified magnetic nanoparticles as "spreading solutions", Langmuir monolayers of these particles were formed. Multiparticle layered structures were constructed by the Langmuir-Blodgett (LB) technique. The fabrication of single- and multiparticle layers of organo-modified magnetic nanoparticles was investigated using surface pressure-area (π-A) isotherms, out-of-plane X-ray diffraction (XRD), in-plane XRD, and atomic force microscopy (AFM). The out-of-plane XRD profile of a single-particle layer of organo-modified Fe3O4 clearly showed a sharp peak which was attributed to the distance between Fe3O4 layers along the c-axis. The AFM image of single-particle layer of organo-modified CoFe2O4 revealed integrated particle organization with a uniform height; these aggregated particles formed large two-dimensional crystals. For both nanoparticle species, regular periodic structures along the c-axis and high-density single-particle layers were produced via the Langmuir and LB techniques.
Multiferroic Co-substituted BiFeO3 films were fabricated by chemical solution deposition method followed by post deposition annealing at various temperatures. The substitution of cobalt of B-sites for iron in BiFeO3 was promoted at relatively high temperatures. The B-site substitution by cobalt promoted increases in saturation magnetization and spontaneous magnetization. By substitution, leakage current density was suppressed in a high-electric-field region, and ferroelectric hysteresis (P–E) loops became measurable even at room temperature. The optimal annealing temperature for the coexistence of a high remanent polarization and a high remanent magnetization was 923 K having a high B-site substitution ratio of cobalt.
We have investigated the synthesis conditions and the magnetic properties of X-type hexagonal ferrites. It is found that Ba2Cu2Fe28O46 (Cu2X), Ba2Co2Fe28O46 (Co2X), and Ba2Ni2Fe28O46 (Ni2X) ferrites can be synthesized at a sintering temperature of 1250 °C. The x-ray diffraction patterns for Cu2X, Co2X, and Ni2X samples are in good agreement with the pattern calculated from the atomic coordinates for Ba2Fe30O46 (Fe2X), where two diffraction peaks at Q=2.24 and 2.30 Å−1 are clearly observed in contrast with other M-, W-, Y-, and Z-types hexagonal ferrites. It is also found that the low-temperature spontaneous magnetizations of Cu2X, Co2X, and Ni2X ferrites are 47.5 μB/f.u., 43.4 μB/f.u., and 43.2 μB/f.u., respectively. The cation distributions for Cu2X, Co2X, and Ni2X are discussed within the model of a Néel-type collinear ferrimagnetic structure.
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