Magnetic Field and Magnetic Isotope Effects upon Reactions of Heavy Atom-Centered Radicals

We present our recent studies on magnetic field effects (MFEs) observed in reactions of heavy atom-centered radicals such as Si-,P-, Ge-, and Sn-radicals with a ns-laser photolysis technique under magnetic fields of 0–10 T. Although the MFES of heavy atom-centered radicals are much smaller than those of C-radicals due to the spin-orbit interaction of heavy atoms, we have found appreciable MFEs in many reactions of such heavy atom-centered radicals. Comparing the MFES of C-radicals with those of heavy atom-centered ones, we have explained the MFEs of heavy atom-centered radicals in terms of the Δg and relaxation mechanisms. We have found that the separation between the MFES due to the Δg mechanism and those due to the relaxation one is possible with the enhancement of spin relaxation by the addition of a paramagnetic ion. We have also tried to enrich magnetic isotopes of heavy atoms with the magnetic isotope effect (MIE), using the reactions which show fairly large MFES. Recently, we have succeeded in enriching ⁷³Ge. This is the heaviest isotope which has so far been enriched with the MIE from samples of natural abundance.     

Single Phase Formation,Cation Distribution,and Magnetic Characterization of Coprecipitated Nickel-Zinc Ferrites

X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry were used to investigate the structural, morphological, and magnetic properties of Ni_1-xZn_xFe₂O₄ nanosubmicron powders (x = 0–0.8). The samples were prepared by a coprecipitation method at temperatures between 600 and 1100 degree Celsius for five hours. The lattice constant, average size of coherent scattering regions, and cation distribution were analyzed by Rietveld refinement of the X-ray diffraction measurements. Scanning electron micrographs showed that the particle size increased from the nano- to the submicron scale as the zinc content increased from x = 0 to x = 0.8. The magnetization as functions of temperature and applied magnetic field were measured on the single-phase samples obtained at an annealing temperature of 1100 degrees Celsius. The derived saturation magnetization and Curie temperature were compared to those of the bulk counterparts reported previously and discussed based on finite-size effects and possible nonmagnetic impurities. The influence of zinc substitution on the magnetic exchange interactions were studied based on molecular-field theory for compositions of 0 ≤x ≤ 0.4.     

Temperature Calibration of TMAs Using Modulated Temperature and Curie Temperature Reference Standards

This article presents the concept of calibrating temperature in thermomechanical analyzers (TMA) using reference standard magnetic materials whose Curie temperatures are well-known. This concept has not been tested experimentally to the best of the author's knowledge. Electrical current applied to a unifilarly wound furnace results in the furnace acting as an electrical inductor. A magnetic material sample located within such a furnace practically constitutes a solenoid core. A modulated temperature program directly results in a corresponding varying force exerted by the sample against the TMA probe, if the probe's axis and the central induced magnetic field line of force are coaxial, and, furthermore, if the direction of the central magnetic field line of force and the expansion direction of the probe are identical. If a sample undergoes a Curie transition, then the force which the sample exerts against the probe will diminish to zero as the transition goes to completion. Using a modulated temperature program throughout this phase transition allows determination of transition completion, by observation of the point at which the force required to maintain the sample's physical position reaches a steady state from it's previously non-steady state. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magneto-responsive nanocomposites: Preparation and integration of magnetic nanoparticles into films,capsules, and gels

This review reports on the latest developments in the field of magnetic nanocomposites, with a special focus on the potentials introduced by the incorporation of magnetic nanoparticles into polymer and supramolecular matrices. The general notions and the state of the art of nanocomposite materials are summarized and the results reported in the literature over the last decade on magnetically responsive films, capsules and gels are reviewed. The most promising concepts that have inspired the design of magneto-responsive nanocomposites are illustrated through remarkable examples where the integration of magnetic nanoparticles into organic architectures has successfully taken to the development of responsive multifunctional materials.     

含双噻唑自组装膜的制备及磁性能研究

以2,2′-二氨基-4,4′-联噻唑(DABT)和苯酚为原料合成了新型的偶氮化合物2,2′-对苯酚偶氮基-4,4′-联噻唑(BTDP),将其与聚二甲基二烯丙基氯化铵(PDDA)在聚乙烯(PE)膜上进行层层自组装,并与过渡金属离子进行了配位.UV-Vis和FT-IR表征发现这种膜可以均匀的进行组装,且能较好的与金属离子配位.多功能材料物理特性测量系统(physical property measurement system,PPMS)测定配合物的磁性能,测试结果表明,与两者溶液直接混合后沉淀配合物的磁性相比,在PE膜上形成的自组装膜配合物的磁性能有较大幅度的提高.     

Mild hydrothermal synthesis,isomorphous substitution,crystal structure characterization and magnetic properties of BaMP2O7 (M = Mn,Cu)

At mild hydrothermal conditions triclinic modifications of BaMP₂O₇ (M = Mn and/or Cu) have been succeeded. The method offers cheap, one step, impurity free and chemical flexible fabrication of family of metal phosphates that are potential low-dimensional quantum magnets. Partial isomorphous substitution of the Mn²⁺ by Cu²⁺ resulted into mixed-metal solid that has been structurally and magnetically characterized. Rietveld refinement study confirmed the structures and revealed the influence of transition metal substitution. The temperature-dependent magnetic measurements revealed that the system is paramagnetic in almost all temperature range and an apparent antiferromagnetic phase transition occurs around 5 K. Using the Curie–Weiss law, a Curie–Weiss temperature, θ_P = −11.0 K, and a Curie constant C = 3.39 emu K mol⁻¹ was obtained. The small negative θ_P value and the χT behavior as a function of temperature reveal a weak antiferromagnetic interaction between the Cu²⁺/Mn²⁺magnetic centers.     

Electro-less plating nickel-phosphorus of low carbon steel using various pretreatments and an external magnetic field

Electro-less plating nickel-phosphorus (EPNP) subject to various pretreatments and an external magnetic field, are prepared onto low carbon steel (LCS). The surface hardness (SH), fatigue life (FL) and corrosion behavior (CB) of Ni-P coated are respectively obtained using a nano-indenter and a high strain low cycle fatigue life (HSLCFL) and polarization test. The experimental outcome reveals that LCS substrates that are pretreated using the proposed acid mixture (25% H₂SO₄ + 5% HCl) roughening and activation allow good Ni-P films to be deposited. In terms of EPNP, as the P content decreases, the SH and FL increase. Specimens that a coated in a Ni–P film using an external magnetic field have better mechanical performance than those that are not produced in an external magnetic field. As the external magnetic field intensity is increased, the film thickness, SH and FL increase, the concentration of P decreases and thin grains are formed on the film surface. The specimens without using an external magnetic field that are coated with a Ni–P film exhibit better resistance to corrosion than the uncoated sample of LCS. However, the Ni–P film that is coated using an external magnetic field has higher SH, so it exhibits increased resistance to corrosion.     

磁场对微乳液法合成聚苯胺结构及其电化学行为的影响

在不同磁场强度下,采用微乳液聚合法合成导电聚苯胺(PANI),以碳纸负载PANI为工作电极,通过循环伏安测试方法,探讨了磁场、氧化剂浓度和聚合时间对微乳液聚合法合成PANI电化学性能的影响;并通过X射线衍射(XRD)、四探针电导率测试和傅立叶红外光谱(FTIR)对产物结构和性能的表征分析,印证了循环伏安分析结果的可靠性.实验结果表明,与无磁条件下制备的PANI相比,磁场条件下制备的PANI具有较高的导电性和规整度;FTIR谱图分析表明,由于磁场的取向作用使分子间相互作用力降低,分子链离域程度增大,使磁场条件下合成PANI的主要特征峰有向低频方向移动的趋势,但分子的基本结构单元没有发生变化.研究结果显示,利用负载PANI的碳纸为工作电极,能够对微乳液法合成PANI的电化学行为进行有效的实时表征.     

Magnetic properties of lanthanide chalcogenide semiconducting nanoparticles

To understand the importance of the band gap to the magnetic ordering in magnetic semiconductors, we have studied the effect of particle size on the ferromagnetic Curie temperature in semiconducting EuS. We have synthesized capped approximately 20 nm EuS nanoparticles using a single-source precursor, [Eu(S(2)CN(i)()Bu(2))(3)Phen] decomposed in trioctylphosphine. The nanoparticles have been characterized by X-ray powder diffraction, TEM, and magnetic susceptibility measurements as a function of temperature and field. The Curie temperature, based on Arrott plots, is depressed by 1-2 K from the bulk value.     

Nuclear and magnetic structures and magnetic properties of the layered cobalt hydroxysulfate Co5(OH)6(SO4)2(H2O)4 and its deuterated analogue, Co5(OD)6(SO4)2(D2O)4

The structures (nuclear and magnetic), magnetic properties (2-300 K, 1-10(4) bar), and heat capacity of the layered ferromagnet Co5(OH)6(SO4)2(H2O)4 are reported. The crystal structure consists of brucite-like M(II)-OH layers of edge-sharing octahedra, but having two different Co sites, which are pillared by ...O3SO-Co(H2O)4-OSO3.... The absorption spectrum confirms the presence of divalent Co, and by comparison of the two isotopic materials, the assignment of the vibrational spectra is proposed. The magnetic properties are those of a ferromagnet with a Curie temperature of 14 K. Temperature and field dependence magnetization data taken on an aligned sample suggest an easy-plane magnet. The Curie temperature increases linearly with pressure at a rate of +0.12 K/kbar, suggesting small progressive and uniform modifications of the Co-Co exchange interactions. Rietveld refinement of the neutron powder diffraction data and consideration of a group analysis reveal the direction of the moments of the Co within the layer to be along the b-axis, with a maximum moment of 3.33 micro(B) per cobalt. Those of the pillars remain random. Estimation of the entropy from the heat capacity data accounts for the presence of four ordered moments of Co with spin 1/2 at the long-range ordering temperature, while the moment of the pillaring Co contributes only at lower temperature due to the increase of the internal field as the temperature is lowered. The purely 2D-magnetic ordering in an easy-plane magnet, evidenced by neutron diffraction and heat capacity, challenges the existing theories and is a rare example of a single-layer magnet.     

Synthesis,Crystal Structure and Properties of RbMnO2

RbMnO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursers (Mn₂O₃, RbN₃ and RbNO₃) were heated in a special regime up to 600 °C and annealed at this temperature for 30 h in specially designed silver crucibles. Single crystals have been grown by annealing a 1:1 mixture of Rb₂O and MnO_x at 585 °C for 1200 h. According to the crystal structure determination Mn³⁺ is in a square‐pyramidal coordination by oxygen. These [MnO₅] units form double chains extending along the crystallographic c‐axis. RbMnO₂ shows Curie‐Weiss behaviour down to ～ 100 K. A fit of the susceptibility data yields an average value of the magnetic moment (per manganese atom) of μ_eff = 5.33 μ_B, and θ_p = –820 K. At 50 K and low field strength onset of ferromagnetic order due to spin canting has been observed.     

铽锰基化合物TbMn6Sn6的结构和磁性

研究了重稀土金属化合物ＴｂＭｎ６Ｓｎ６的晶体结构、内禀磁性及其矫顽力随和外场变化的规律。ＴｂＭｎ６Ｓｎ６为ＨｆＦｅ６Ｇｅ６型六角型结构，晶格常数为：ａ＝０．５５６１ｎｍ，ｃ＝０．９０４７７ｎｍ，单胞体积为０．２４１ｎｍ＾３，居里温度ＴＣ＝４２１Ｋ。ＴＭｎ６Ｓｎ６化合物在外场较弱时，热磁曲线呈亚铁磁性；当外场较强时，则表现出铁磁行为，具有变磁性，ＴｂＭｎ６Ｓｎ６的矫顽力随温度变化，当温度Ｔ＝２００Ｋ     

The force acting on a superparamagnetic bead due to an applied magnetic field

This paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.     

A new simple instrument for thermomagnetometry. Applications to simultaneous thermomechanical measurements

A new instrument has been set up to study magnetic materials. Curie points measured by means of this simple apparatus are in perfect agreement with those given by a conventional magnetic balance. The apparatus may be used alone, but also combined with an electronic thermodilatometer. Curie points are emphasized simultaneously by the thermodilatometric and impedance curves. It appears that the sensitivity and reliability of the apparatus demonstrate magnetic phenomena of very low intensity such as the order point of α-Fe₂O₃.     

Synthesis and Magnetic Properties of Novel Azamacrocyclic LnIII,CuII, FeIII,and SrII Complexes and Conformational Analysis of the Ligands

Hexaalkoxy‐substituted azamacrocyclic metal complexes 1 · MX_n [MX_n = FeCl₃, CuCl₂, SrCl₂, Ln(NO₃)₃; Ln = La, Pr, Eu, Ho, Er] with various chain lengths were prepared by a convergent approach using 1,2‐bisalkoxy‐4,5‐diamines 3 and 4‐alkoxy‐pyridine‐2,6‐dicarbaldehydes 4 as key building blocks for template‐assisted cyclocondensation. Metal complexes 1 · MX_n were considered as potential metallomesogens. However, differential scanning calorimetry and optical polarizing microscopy of 1 · MX_n did not reveal any mesomorphism. The magnetic susceptibility shows deviation from Curie‐like behavior. Due to ligand field effects the effective magnetic moments are a function of the temperature. In order to obtain structural informations on the free ligand 1 , which is synthetically not accessible, theoretical calculations were carried out. For the free azamacrocycle 2a and the free hexamethoxy‐substituted azamacrocycle 1a the IR spectra were computed at the level of density functional theory. A planar and a saddle‐shaped conformation was considered. The IR spectra and especially the dependence of the C=N vibration on the structural parameters and the charge distribution are discussed.     

A magnetically controlled MEMS device for drug delivery: design, fabrication, and testing

We report the development of a magnetically controlled drug delivery device for on-demand drug release to treat chronic diseases. The devices consist of drug-loaded micro-reservoirs (6 mm in diameter and ～550 μm in depth), sealed by magnetic PDMS (polydimethylsiloxane) membranes (? 6 mm × 40 μm) with laser-drilled apertures and actuated by an external magnetic field. We present a detailed analysis of the magnetic actuation forces and provide an estimate of the resulting membrane deflections. The reservoirs are fabricated by PDMS molding and loaded with drugs using solvent evaporation methods. Post-processing procedures using bovine serum albumin (BSA) adsorption on magnetic PDMS surfaces are carried out to modify the surface wettability and to allow water filling and dissolution of the drugs in the reservoirs. Detailed surface modification processes are described and characterized. The device demonstrates on-demand delivery of methylene blue (MB) as a model drug. Intermittent magnetic actuations of the device in a ～200 mT magnetic field show 10-fold increase in MB release compared to background release when the device is not actuated.     

聚γ-(2-脲基噻唑)丙基甲基硅氧烷金属配合物的制备及磁学性能研究

合成了一种新的γ-(2-脲基噻唑)丙基甲基二乙氧基硅烷单体及聚硅氧烷聚合物,采用溶胶-凝胶法制备了聚硅氧烷的铜、镍金属离子的配合物,利用红外光谱、核磁共振氢谱及质谱等手段表证了其结构.并分析和讨论了它们的磁学性能.此类金属配合物在低温区,磁化率倒数与温度的关系不服从居里-外斯定律,存在着铁磁耦合,是一类有机铁磁体.另外,发现在含噻唑基团的硅氧烷链中引入5倍当量的二甲基硅氧烷链节,其居里-外斯温度增大了近2倍.     

Ni ion-containing immobilized ionic liquid on magnetic Fe3O4 nanoparticles: An effective catalyst for the Heck reaction

In this work, we synthesized Ni²⁺-containing 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride ionic liquid on magnetic Fe₃O₄ nanoparticles. The catalytic activity of these novel nanocomposites was finally evaluated for the Heck reaction at 100 °C, and can be reused after washing without loss in activity. The immobilized ionic liquid catalysts proved to be effective and easily separated from the reaction media by applying an external magnetic field. This procedure has many obvious advantages compared to those reported in the previous literature, including avoidance of the use of the expensive Pd catalysts, mild reaction conditions, high yields, and simplicity of the methodology.     

(Gd1-xREx)5Si4(RE=Dy, Ho)系列材料磁熵变研究

对 (Gd1-xDyx)5Si4(x=0.1, 0.2, 0.3, 0.35) 和(Gd1-xHox)5Si4(x=0.05, 0.15, 0.25)系列合金的居里温度、磁相变、磁熵变等磁性质进行了研究. 结果发现 该系列合金保持了Gd5Si4的Sm5Ge4正交型晶体结构, 居里温度随着引入的x量的增加而呈近似线性减小趋势;在居里温度附近样品的磁特性符合二级相变规律;通过调节Dy 或Ho的含量调节居里点, 样品中不含贵重元素Ge, 大大降低了成本;在较宽的温度范围和低场下(＜2 T)具有较大的磁熵变值从而使其适合于被制成梯度功能复合材料. 研究表明 (Gd1-xREx)5Si4(RE=Dy, Ho)系列材料有望成为较好的室温低场磁制工质.