R_2Fe_(14)B的磁性

在1985年3月31日～4月3日举行的日本物理学会第40届年会上,东北大学金属材料研究室(简称“东北大金研”)和住友特殊金属公司(简称“住友特金”)的山口、山本、佐川、広沢哲等人,发表了他们研究新型永磁材     

R_2Fe_(14)B化合物的结构和磁性

以R_2Fe_(14)B四方相(R=稀土元素)为基的R-Fe-B磁体已发展成为磁性能最高,具有工业意义的永磁材料.本文论述了R_2Fe_(14)B四方相的晶体结构,居里点,磁化强度与原子磁矩以及各向异性的最新研究结果和进展。     

Nd_2Fe_(14)B/α-Fe交换耦合双层薄膜磁性能

利用微磁学理论模拟计算了Nd2Fe14B/α-Fe交换耦合双层膜的磁滞回线,并对双层膜体系的剩磁、矫顽力、最大磁能积与软磁层厚度的关系进行了研究。结果显示,软磁层厚度小于临近尺寸时,磁滞回线为矩形,双层膜完全耦合;软磁层厚度与磁性能的关系表明,随着软磁层厚度的增加,剩磁和最大磁能积先增大后减小,而矫顽力单调下降。     

Synthesis and Characterization of Nanocapsules of α-Fe(NiCoAl) Solid-solution

α-Fe(NiCoAl) solid-solution nanocapsules were prepared with pure powders of Fe, Ni, Co and Al by the plasma arc-discharging using a copper crucible. The shapes of the nanocapsules are in polyhedrons with the core/shell structure. The body centered cubic (BCC) phase is formed in the core. The size of the nanocapsules is in the range of 10～120 nm and the thickness of the shell is 4～11 nm. Saturation magnetization Js=150 Am2/kg and coercivity iHC=24.3 kA/m are achieved for the nanocapsules.     

Synthesis and Characterization of Nanocapsules of α-Fe(NiCoAl) Solid-solution

α-Fe(NiCoAl) solid-solution nanocapsules were prepared with pure powders of Fe, Ni, Co and Al by the plasma arc-discharging using a copper crucible. The shapes of the nanocapsules are in polyhedrons with the core/shell structure. The body centered cubic (BCC) phase is formed in the core. The size of the nanocapsules is in the range of 10-120 nm and the thickness of the shell is 4-11 nm. Saturation magnetization JS=150 Am2/kg and coercivity iHC=24.3 kA/m are achieved for the nanocapsules.     

Ordering of the α-Fe(Si) Crystallization Phase in Annealed Fe_(73.5)Cu_1Mo_3Si_(13.5)B_9 Alloy

The ordering of the α-Fe(Si) crystallization phase in annealed Fe73.5Cu1Mo3Si13.5B9 alloy has been studied using XRD method. The α-Fe(Si) phase in Fe73.5Cu1Mo3Si13.5B9 alloy annealed at 460℃ for 1 h consists of the DO3-type ordered region with spherical shape and disordered region. The size of DO3 ordered region increases with the annealing temperature. When the annealing temperature is 560℃, the size of the ordered region in the α-Fe(Si) grain is 14.0nm,which is nearly as large as that of the α-Fe(Si) grain (14.2 nm) and the degree of order of the α-Fe(Si) phase is about 0.78. When Fe73.5Cu1 Mo3Si13.5B9 amorphous alloy is annealed at 520℃, with the increment of the annealing time, the shape of the DO3 ordered region in the α-Fe(Si) phase is spheroidal at the beginning of the annealing and becomes spherical and has asize of 12.8 nm when the annealing time is 60 min. In addition, the DO3 superlattice lines of the α-Fe(Si) phase will vanish if Fe73.5Cu1Mo3Si13.5 B9 amorphous alloy is annealed for 1 h at 750℃.     

Precipitation of α″-Fe_(16)N_2 Phase

Characteristics of the precipitate α″-Fe16N2 phase have been investigated by X-ray diffraction and TEM analysis. VSM measurements give the saturation magnetization of the α″ phase.     

Synthesis and gas sensing properties of α-Fe(2)O(3)@ZnO core-shell nanospindles

α-Fe(2)O(3)@ZnO core-shell nanospindles were synthesized via a two-step hydrothermal approach, and characterized by means of SEM/TEM/XRD/XPS. The ZnO shell coated on the nanospindles has a thickness of 10-15 nm. Considering that both α-Fe(2)O(3) and ZnO are good sensing materials, we have investigated the gas sensing performances of the core-shell nanocomposite using ethanol as the main probe gas. It is interesting to find that the gas sensor properties of the core-shell nanospindles are significantly enhanced compared with pristine α-Fe(2)O(3). The enhanced sensor properties are attributed to the unique core-shell nanostructure. The detailed sensing mechanism is discussed with respect to the energy band structure and the electron depletion theory. The core-shell nanostructure reported in this work provides a new path to fabricate highly sensitive materials for gas sensing applications.     

Fabrication, growth mechanism, and characterization of α-Fe(2)O(3) nanorods

This work reports the facile synthesis of α-Fe(2)O(3) nanorods and nano-hexagons and its application as sunlight-driven photocatalysis. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), diffused reflectance spectroscopy (DRUV-vis), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The phase and crystallinity were confirmed from the XRD study. Electron microscopy study clearly indicates the formation of different morphologies of nanocrystals. These hematite nanostructures were used as a model system for studying the shape-dependent photocatalytic degradation of phenol, methylene blue, and congo red. Amongst all the nanostructured semiconductors, Pt-doped hematite nanorod showed 55% efficiency towards the decolonization of methylene blue and 63% toward congo red under sun light illumination. The difference in photocatalytic activity is discussed in terms of their crystallize size and morphological ordering.     

Microstructure,Magnetic Properties,and Thermal Stability of Bulk Anisotropic SmCo7/α-Fe(Co) + Nd2Fe14B/α-Fe Multiphase Nanohybrid Magnets

Journal of Superconductivity and Novel Magnetism - In this report, we have fabricated anisotropic bulk SmCo7/α-Fe(Co)?+?Nd2Fe14B/α-Fe multiphase nanohybrid magnets using...     

R_2Fe_(14)B的3d磁性的穆斯堡尔谱学研究

根据布居数和铁的磁矩μ~[3],求得250K 以及其它温度下铁的亚点阵的~(57)Fe 穆斯堡尔参数。通过确立的超精细场 Hn 和μ的关系,得到约化坐标的μ(T)。表明不同铁晶位其对应态不同。实验点落在布里渊曲线之下。交换积分偏差参数△与 Fe-Fe 原子间距的标准偏差 S 呈线性关系,表明近邻原子自旋间的交换作用的静电性质。认为交换积分的起伏导致 R_2Fe_(14)B 的低 T(?)。     

Studies of the changes in the geometry of grain boundaries and grains during recovery/continuous recrystallization in α-Fe

Samples of -Fe (Armco) have been deformed by 50% in compression. These have then been annealed at 400 °C, considerably below the conventional recrystallization temperature, and the evolution of grain size and shape quantified. Initially the grain size is found to decrease whilst, at the same time, the grain-shape anisotropy also decreases. It is suggested that a continuous recrystallization process which favours the generation of higher angle grain boundaries is the underlying mechanism. Annealing for longer times gives rise to an increase in grain size with the development of undulations on the grain surfaces. The mechanism suggested for this behaviour involves the annihilation of segments of sub-boundaries on to a pre-existing boundary from either side of the boundary.     

Dy_2O_3掺杂对机械球磨Nd_2Fe_(14)B/α-Fe复合磁体矫顽力的影响

用机械球磨法制备Nd_2Fe_(14)B/α-Fe复合磁体,研究了Dy_2O_3掺杂对纳米复合磁体磁性能的影响。结果表明,掺入Dy_2O_3能显著提高复合磁体的矫顽力,且随着Dy_2O_3掺杂量的增大最大矫顽力对应的退火温度降低。X射线衍射分析结果表明,掺入Dy_2O_3使Nd_2Fe_(14)B的晶格常数减小,也即Dy部分替代Nd后生成了(Nd,Dy)_2Fe_(14)B硬磁相。因此,复合磁体矫顽力的增强主要归因于硬磁相磁晶各向异性的提高。但是,硬磁相磁晶各向异性的提高缩短了有效交换耦合长度,表现为过量掺杂Dy_2O_3使矫顽力降低。     

Electrical and Magnetic Properties of the Pr2/3 + xTiO3 ± yPerovskite Phase

The thermoelectric power, electrical resistivity, and magnetic susceptibility of the praseodymium titanium bronze phase Pr_{2/3 + x} TiO_{3 ± y} were measured for compositions in the range 0 x 1/3. The conductivity of the bronze was found to exhibit metallic behavior between 77 and 450 K. The transport data were used to evaluate the electron mobility and Fermi energy. In the range 77–300 K, the magnetic susceptibility of Pr_{2/3 + x} TiO_{3 ± y} consists two contributions—those from Pr³⁺(a strong function of temperature) and Ti³⁺(a weak function of temperature).     

Structural,Magnetic, Optical and Electrochemical Properties of a New Class of α-Fe2O3-Mx-NiFe2O4+δ (M = None,Co2+, Eu3+, Ho3+ and Yb3+) Nanocomposites

Journal of Superconductivity and Novel Magnetism - Synthesis of α-Fe2O3-Mx-NiFe2O4+δ (M?=?None, Co2+, Eu3+, Ho3+ and Yb3+) nanocomposites is reported for the first time by a...     

Synthesis of α-Fe2O3 via oxidative hydrolysis of iron(II) sulphate

The influence of the main reaction parameters (temperature, pH and concentration) in the oxidative hydrolysis of iron (II) sulphate in an acid medium on the properties of the obtained -Fe₂O₃ and its applicability in ferrite production has been studied. The addition of manganese(II) ions catalyses the process in the homogeneous phase, probably by activation of oxygen. The obtained results are discussed within the framework of the assumed reaction mechanism, which includes an homogeneous reaction and a heterogeneous one with the participation of the oxidative hydrolysis product -FeOOH.     

Monodisperse α-Fe(2)O(3)@SiO(2)@Au core/shell nanocomposite spheres: synthesis, characterization and properties

A new hybrid spherical structure α-Fe(2)O(3)@SiO(2)@Au with a size of about 141?nm was designed, with a hematite cubic core surrounded by a thick silica shell and further decorated with gold nanoparticles. The monodisperse α-Fe(2)O(3)@SiO(2) spheres were first prepared by a sol-gel process based on the modified St?ber method. Subsequently, the surface of the α-Fe(2)O(3)@SiO(2) particles was functionalized by-NH(2) functional groups. The electrostatic attraction of -NH(2) groups will attach the negatively charged Au nanoparticles to the amino-functionalized α-Fe(2)O(3)@SiO(2) nanospheres in order to prepare α-Fe(2)O(3)@SiO(2) monodisperse hybrid spheres. The M(H) hysteresis loop for α-Fe(2)O(3)@SiO(2) and α-Fe(2)O(3)@SiO(2)@Au spheres indicates that the nanocomposite spheres exhibit superparamagnetic characteristics at room temperature. The optical properties and the application of these hybrid nanocomposites as catalysts for the conversion of CO to CO(2) have also been studied.