Polyfunctional Two- (2D) and Three- (3D) Dimensional Oxalate Bridged Bimetallic Magnets

Summary.  We report major results concerning polyfunctional two- (2D) and three- (3D) dimensional oxalate bridged bimetallic magnets. As a consequence of their specific organisation they are composed of an anionic sub-lattice and a cationic counter-part. These bimetallic polymers can accommodate various counter-cations possessing specific physical properties in addition to the magnetic ones resulting from the interactions between the metallic ions in the anionic sub-lattice. Thus, molecular magnets possessing paramagnetic, conductive and optical properties are presented in this review. Corresponding author. E-mail: train@ccr.jussieu.fr Received April 11, 2002; accepted May 27, 2002     

Nd-Fe-B永磁材料氢脆过程及Al+Al2O3阻氢涂层研究

从材料保护的角度出发，在分析了Nd-Fe-B永磁材料的氢脆过程及氢脆的特点后，用RF磁控溅射制备一定厚度的Al薄膜并在一定条件下进行氧化处理，得到了Al A12O3复合涂层。用SEM和XBD分析了涂层形貌和组成，并用高压气相充氢的方式测试了涂层的阻氢性能。研究表明，厚度为8．0μm复合涂层的阻氢性能为：在10MPa的H2环境中(25℃)，阻氢时间达65min，且对磁体的磁性能无不良影响。     

Conducting Molecular Magnets Based on TTF-Derivatives

The crystal structures, electronic and magnetic properties of conducting molecular magnets developed in our group are reviewed. (DMET)₂FeBr₄ is composed of alternating stacks of quasi-one-dimensional (1D) donor sheets and square lattice magnetic anion sheets. This salt undergoes an SDW transition of the donor layer at 40 K and an antiferromagnetic transition of Fe³⁺ spins on the anion layer at 3.7 K. The one-to-one correspondence of the anomalies appearing on the magnetization curves with those on the magnetoresistance supports the presence of the π-d interaction. (EDO-TTFI₂)₂[M(mnt)₂] (M=Ni,Pt) consists of 1D chains of conducting donors and magnetic anions aligned in parallel. These salts show metallic conductivity accompanied with a metal-insulator transition around 90 K. Localized spins on the anions behave as a 1D ferromagnet, whose origin is explained by McConnell's first model. The properties of related materials, (EDTDM)₂FeBr₄, (EDS-TTF)₂FeBr₄ and (EDO-TTFBr₂)₂FeBr₄, are also presented.     

金属-自由基分子基铁磁体的设计合成进展

金属一自由基分子基铁磁体的设计和合成，是近年发展起来的新课题，本文介绍这一课题的研究现状与发展趋势。     

Organic and Organometallic Molecular Magnetic Materials—Designer Magnets

Magnets composed of molecular species or polymers and prepared by relatively low-temperature organic synthetic methodologies are a focus of contemporary materials science research. The anticipated properties of such molecular-species-based magnetic materials, particularly in combination with other properties associated with molecules and polymers, may enable their use in future generations of electronic, magnetic, and/or photonic/photronic devices ranging from information storage and magnetic imaging to static and low-frequency magnetic shielding. A tutorial of typical magnetic behavior of molecular materials is presented. The three distinct models (intramolecular spin coupling through orthogonal orbitals in the same spatial region within a molecule/ion, intermolecular spin coupling through pairwise “configuration interaction” between spin-containing moieties, and dipole—dipole, through-space interactions) which enable the design of new molecular-based magnetic materials are discussed. To achieve the required spin couplings for bulk ferro- or ferrimagnetic behavior it is crucial to prepare materials with the necessary primary, secondary, and tertiary structures akin to proteins. Selected results from the worldwide effort aimed at preparing molecular-based magnetic materials by these mechanisms are described. Some organometallic solids comprised of linear chains of alternating metallocenium donors (D) and cyanocarbon acceptors (A) that is, …?D^?+ A^?? D^?+ A^??…?, exhibit cooperative magnetic phenomena. Bulk ferromagnetic behavior was first observed below the critical (Curie) temperature T_c of 4.8 K for [Fe^III(C₅Me₅)₂]^?+ [TCNE]^?? (Me = methyl; TCNE = tetracyanoethylene). Replacement of Fe^III with Mn^III leads to a ferromagnet with a T_c of 8.8 K in agreement with mean-field models developed for this class of materials. Replacement with Cr^III, however, leads to a ferromagnet with a T_c lowered to 3.65 K which is at variance with this model. Extension to the reaction of a vanadium(o) complex with TCNE leads to the isolation of a magnet with a T_c ≈ 400 K, which exceeds the thermal decomposition temperature of the material. This demonstrates that a magnetic material with a T_c substantially above room temperature is achievable in a molecule/organic/polymeric material. Finally, a new class of one-dimensional ferrimagnetic materials based on metalloporphins is discussed.     

高性能含镨快淬(Nd,Pr)12(FeCoZr)82B6粘结磁体的制备

采用过快淬加晶化退火处理的方法,研究了含有Pr的近正分快淬(Nd,Pr)12(FeCoZr)82B6粘结磁体制备工艺,粘结出的磁体磁性能为:Br=0.669T,Hci=811kA·m-1,Hcb=434kA·m-1,(BH)m=75kJ·m-3。合金快淬态的组成和显微结构、晶化退火温度、晶化退火时间直接影响磁体的磁性能,以24m·s-1速度快淬,并在655℃退火10min,可获得最佳磁性能。实验制备的粘结快淬(Nd,Pr)12(FeCeZr)82B6磁体(密度6 1g·cm-3)磁性能为:Br=0 669T,Hci=811kA·m-1,Hcb=434kA·m-1,(BH)m=75kJ·m-3     

Ba2Ca2Cu3Ox Precursor Effects on Synthesis of (Hg,Pb)Ba2Ca2Cu3O8+δ Superconductor

The influence of Ba₂Ca₂Cu₃O_x precursor on the synthesis and properties of (Hg,Pb)Ba₂Ca₂Cu₃O_8+δ has been examined. Fine homogeneous Hg-free precursor powder of Ba₂Ca₂Cu₃O_x of desirable phase composition was prepared by sol-gel method using EDTA acid as a complexing agent. A reproducible superconducting sample of Hg_0.8Pb_0.2Ba₂Ca₂Cu₃O_8+δ with fine-grained, dense microstructure, composed predominantly of (Hg,Pb)-1223 phase and with advantageous magnetic properties, was synthesized by high pressure crystallization in mercury environment of well-calcined Ba₂Ca₂Cu₃O_x precursor. This revised version was published online in July 2006 with corrections to the Cover Date.     

HTS块材与磁场间相互作用估算方法研究

HTS块材电磁机构日趋复杂，为了实现系统结构和电磁设计的优化需要建立一种简单可靠的方法来估算系统内部的相互作用．描述HTS磁学特性通常采用热激活磁通跳跃、磁通流动等系列模型，用其描述相互作用各有优缺点．为此，我们实验测试了HTS块材与永磁间相互作用随空间相对位置变化．并基于HTS完全抗磁性和临界态模型构造的B（H）曲线进行模拟仿真，通过与实验结果的比较．力求寻找一种方便可行、较为准确及可靠的HTS块材与磁场间相互作用估算方法．     

超导薄膜表面电阻测试方法及误差分析

本文介绍一种蓝宝石加载单端短路谐振腔测量高温超导薄膜的方法，并对测量误差进行了较详细的分析．造成测量误差的主要因素有三个：系统无载品质因数Q0的测量误差，超导薄膜以外损耗品质因数Qother的实验误差，以及在谐振腔内超导薄膜的几何参数G的计算误差．大量的实验结果表明，本方法操作简便，重复性好，测量精度高，相对测量误差不超过10％．