A two-phase synthesis technique is developed for high-quality Mn3O4 nanocrystals with morphologies that approach monodisperse spheres and perfect cubes. The cubic nanocrystals gradually evolve into spheres over time at an elevated temperature (see graph). The dependence of magnetic properties on their size and shape is investigated. Moreover, the characteristics and properties of structures formed by self-assembly of the nanoparticles are explored. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2296/2008/z700698_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

采用溶胶-凝胶法制备了不同烧结温度的钙钛矿类锰氧化物La0.67Sr0.33MnO3样品.实验结果表明,在1 573 K以上烧结的样品,晶粒出现异常长大,晶界效应明显.随着烧结温度的提高,磁化强度逐渐增大,但样品的居里温度基本不变.此外,在1 173和1 573 K温度下烧结的样品,均出现了低于居里温度的金属-半导体导电行为转变.在合适的烧结条件下,可以观察到隧道磁电阻(TMR)和超大磁电阻(CMR)2种磁电阻效应.实验表明,自旋电子的输运,不仅与样品平均粒径的大小和密度有关,而且与晶界的微观结构有密切关系.

The ordered double perovskites SrLaMnBO_(6)(B:Mo,W) were prepared by sol-gel reaction.The XRD results suggest that the crystal structure of SrLaMnMoO_(6) belongs to the monoclinic P2_(1)/n space group and that of SrLaMnWO_(6) belongs to the tetragonal I4/m space group.The competition between band filling effect and steric effect results in the expansion of cell volume for SrLaMnBO_(6)(B:Mo,W).Magnetic measurements indicated that both samples showed very weak ferro-/ferrimagntism,but the magnetic moments at H=0(extrapolated) from the magnetic moment vs applied magnetic field curves are 0.72μ_(B) and 0.16μ_(B) for SrLaMnMoO_(6) and SrLaMnWO_(6),respectively,much smaller than the expected net magnetic moments.From the(temperature) dependence of magnetization for SrLaMnMoO_(6),ferromagnetic-paramagnetic transition is(observed),which is not shown for SrLaMnWO_(6).

The ordered double perovskites, Sr2 – xLaMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2 – xLaxMnMoO6 (0 ≤ x ≤ 1). The compounds have a monoclinic structure (space group P21/n) and the cell volume expands monotonically with La doping. The Tc and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2 – xLaxMnMoO6 decreases only at low doping levels (x ≤ 0.2); while at high doping levels (0.8 ≤ x ≤ 1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.

The single-phase double perovskites Sr2MWO6 (M=Co, Ni) were prepared by sol-gel method. Crystal Structure, magnetic properties and the morphology of Sr2CoWO6 and Sr2NiWO6 were investigated. X-ray powder diffraction (XRD) analysis shows single phase structure for Sr2MWO6 (M=Co, Ni) without any traces of impurities and the crystal structure of all the samples belongs to the tetragonal I4/m space group. SEM image for Sr2MWO6 (M=Co, Ni) indicate that the grains are homogeneous and connect each other very well. The Neel temperature for Sr2CoWO6 and Sr2NiWO6 are 23 K and 59 K, respectively. Magnetic measurements showed that the magnetic moment in these double perovskites originates mainly from the interactions between Ni ions and Co ions.

. The surface topography of thin diblock copolymer films is studied by atomic force microscopy (AFM). With AFM an island-to-ribbon transition is observed for symmetric polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) on mica with increasing solution concentration. Our study also demonstrates how the formation of the pattern strongly depends on the copolymer composition based on the volume fraction. The substrate and solvent used both have great effects on the morphology of the thin films. Only by using highly polar substrate (mica), can we gain regular pattern. The reason why the regular islands cannot be obtained with symmetric PS-b-P4VP on graphite is also explained. On mica using nonselective and selective solvents, a rather regular pattern can be obtained. The difference is only in the solution concentration for forming regular patterns.