Hexagonal Ferrites from Melts and Aqueous Solutions,Magnetic Recording Materials

Owing to their particular crystallographic properties, ferrimagnetic hexagonal ferrites exhibit a far greater coercive force than the conventional magnetic pigments. They therefore appear to be suitable for use in magnetic information storage procedures, some of which are novel and are at the development stage. Thus, magnetic tapes of high coercive force containing barium ferrite could be used as master tapes for copying magnetic information or for producing forgery-proof magnetic cards, if magnetic heads having high-order write fields were successfully developed. Moreover, platelet-like ferrite pigments in which the preferred direction of magnetic orientation is perpendicular to the plane of the platelet are of great interest for perpendicular magnetic recording. In this progress report, the crystal structures, magnetic characteristics of hexagonal ferrites, and chemical processes for their production are discussed. In particular, reactions in salt melts or under hydrothermal conditions produce finely divided pigments whose particles have a pronounced hexagonal, plate-like habit, a narrow particle size distribution, and advantageous magnetic properties. The magnetic properties of the pigments crystallized from salt melts may be adjusted by cation exchange.     

Synthesis and magnetic properties of liquid crystalline lanthanide complexes with alkylsulfate counterions

The reaction of Schiff"s base L with lanthanide alkylsulfates affords liquid crystalline complexes with the general formula L₃Ln(C_nH_2n+1OSO₃)₃. The liquid crystalline structure and magnetic properties are studied by polarization thermal microscopy, differential scanning calorimetry, X-ray diffraction, and measurement of magnetic susceptibility. The temperatures of the existence of the mesophase and magnetic anisotropy of the complexes with the same lanthanide depend on the chain length of the alkyl fragment in the sulfate anion.     

Crystal structure, oxidation state and magnetism of La1.2Sr2.4RuO7: a new member of the [A2O][AnBn−1O3n] series of hexagonal perovskites

Single crystals of the new compound La_1.2Sr_2.4RuO₇, an oxide related to the hexagonal perovskites, were grown from a BaCl₂ flux. The structure was solved by single crystal X-ray diffraction. La_1.2Sr_2.4RuO₇ crystallizes in the space group with a=5.760(1) Å and c=18.273(3) Å. It is one of the rare examples of oxides with isolated RuO₆-octahedra. The structure consists of alternating layers of RuO₆-octahedra and trigonal (La,Sr)O₆-prisms. These prisms are capped by one additional oxygen ion, which occupies a distorted position within the (La,Sr)O₆-layers. La_1.2Sr_2.4RuO₇ is the second member of the general [A₂O][A_nB_n−1O_3n] family of hexagonal perovskites with n=2 and the first ruthenate possessing this structure. XANES investigations, bond valence sum calculations and magnetic measurements show that ruthenium takes the oxidation state +5. Although the ruthenium ions have quite long distances, a medium strong antiferromagnetic interaction between these paramagnetic centers was observed.     

Synthesis and characterization of monodisperse magnetic composite particles for magnetorheological fluid materials

Monodisperse magnetic composite particles (MCP) were prepared and characterized for a study of magnetic field-responsive fluids. Magnetic composite particles used are iron oxide-coated polymer composite particles, which were synthesized through in situ coating of iron oxide onto pre-existing polymer particles by the reduction of ferrous fluids. For a uniform and bulk coating of iron oxide, the porous structure was introduced into the substrate polymer particles through a two-step seeded polymerization method. Moreover, surface cyano-functionality was born from acrylonitrile unit of substrate polymer and it played an important role in obtaining successful uniform coating. The structure of the composite particle was analyzed by using a thermo gravimetric analysis (TGA) and a X-ray diffraction (XRD) analysis. The magnetization property of the particle was also observed. Then, the rheological properties of monodisperse magnetorheological (MR) suspensions of magnetic composite particles were examined under a magnetic field using a parallel-plate type commercial rheometer. From the rheological measurements, it was found that MR properties of the magnetic composite suspensions are dependent on the iron oxide content and the fluid composition.     

Characterization of quasi-one-dimensional S=1/2 Heisenberg antiferromagnets Sr2Cu(PO4)2 and Ba2Cu(PO4)2 with magnetic susceptibility, specific heat, and thermal analysis

Properties of Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ having [Cu(PO₄)₂]_∞ linear chains in their structures with Cu-O-P-O-Cu linkages were studied by magnetic susceptibility (T=2-400 K, H=100 Oe) and specific heat measurements (T=0.45-21 K). Magnetic susceptibility versus temperature curves, χ(T), showed broad maxima at T_M=92 K for Sr₂Cu(PO₄)₂ and T_M=82 K for Ba₂Cu(PO₄)₂ characteristic of quasi-one-dimensional systems. The χ(T) data were excellently fitted by the spin susceptibility curve for the uniform S=1/2 chain (plus temperature-independent and Curie-Weiss terms) with g=2.153(4) and J/k_B=143.6(2) K for Sr₂Cu(PO₄)₂ and g=2.073(4) and J/k_B=132.16(9) K for Ba₂Cu(PO₄)₂ (Hamiltonian H=JΣS_iS_i+1). The similar J/k_B values were obtained from the specific heat data. No anomaly was observed on the specific heat from 0.45 to 21 K for both compounds indicating that the temperatures of long-range magnetic ordering, T_N, were below 0.45 K. Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ are an excellent physical realization of the S=1/2 linear chain Heisenberg antiferromagnet with k_BT_N/J<0.34% together with Sr₂CuO₃ (k_BT_N/J≈0.25%) and γ-LiV₂O₅ (k_BT_N/J<0.16%). Sr₂Cu(PO₄)₂ and Ba₂Cu(PO₄)₂ were stable in air up to 1280 and 1150 K, respectively.     

纤维素基磁性聚偕胺肟树脂的研究——锌副族金属离子在树脂上的吸附

研究了Ｚｎ２＋、Ｃｄ２＋、和Ｈｇ２＋离子在碱式纤维素基磁性聚偕胺肟树脂（ＢＭＡＯ）上的吸附动力学。结果表明，吸附速度受粒内扩散所控制。测得粒内扩散系数分别是１．２２×１０－４、２．４２×１０－４和３．９０×１０－４ｃｍ２·ｓ－１；Ｈｇ２＋离子在树脂上的吸附行为符合Ｆｒｅｕｎｄｌｉｃｈ和Ｌａｎｇｍｕｉｒ等温吸附方程；浓集因数随Ｈｇ２＋离子浓度降低而上升，有利于从稀溶液中除去Ｈｇ２＋离子。将树脂加至Ｚｎ２＋、Ｃｄ２＋或Ｈｇ２＋离子浓度为５０ｐｐｍ的溶液中，离子去除率分别是９６．１、９９．９和９９．３％。     

苯乙烯-异戊二烯嵌段共聚物分子运动的脉冲核磁共振研究

用西德Bruke,MSL-300核磁共振谱仪研究了三个不同系列的苯乙烯-异戊二烯嵌段共聚物的固体回波谱。用PASCAL语言在谱仪提供的计算机上、用线性最小二乘法回归分析把实验曲线分解成快速和慢速两个组分,它们分别对应于嵌段共聚物中刚性相和流动相,从而给出样品两相结构的定性定量信息。     

Functional models of [Fe—S] nitrosyl proteins

The review surveys methods for the synthesis, as well as structures and properties of sulfur-containing iron nitrosyl complexes serving as models of active sites of [Fe—S] nitrosyl proteins, which are potential donors of nitrogen monoxide.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2326–2345, November, 2004.     

稀土化合物Ho2Co14Fe3的磁性分析

在分析稀土磁性常用的哈密顿中，引入了自旋－自旋偶极作用，用参数拟合的方法对Ｈｏ２Ｃｏ１４Ｆｅ３的磁化曲线进行了分析，计算结果与实验数据符合得很好，并且提示了Ｈｏ２Ｃｏ１４Ｆｅ３磁矩的突变现象。     

Can magnetic circular dichroism tackle the problem of site symmetry in solutions?

A new approach to unravel the site symmetry of lanthanides in solutions is presented. The magnetic circular dichroism spectra of Eu³⁺ in the symmetries D_3h, C_4v and D_2d are simulated. In these simulations, the main idea is to introduce the magnetic field along a 3-fold axis, being the resultant of the three equivalent X-, Y- and Z-direction of a cube. This implies that the parallel and perpendicular Zeeman effects are taken into account simultaneously.