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     

Quenchability and Magnetic Properties of Nd_4Fe_(82)B_(14)

The glass forming ability (GFA), crystallization behaviour and magnetic properties of Nd4Fe82B14 produced by melt spinning were investigated. The experimental results show that the GFA is rather Strong; the crystals precipitation sequence is as follows: Am(amorphous)→Am'+bcc-Fe →Nd2Fe23B3+Fe23B6+bcc-Fe→Fe23B6+Fe3B+Nd2Fe14B+bcc-Fe→Fe3B+Nd2Fe14B+bcc-Fe. The magnetic properties after crystallization are not affected by the cooling rate and the best magnetic properties are Br=0.8436 T, Hcj=266.4 kA/m, (BH)max=48.08 kJ/m3.     

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纳米双相复合永磁体研究进展

阐述了Nd2Fe14B/α-Fe纳米双相复合永磁体的磁学特性、制备方法及矫顽力机制;并结合近年来纳米复合永磁体研究的新进展,讨论了制备工艺,添加合金化元素,微结构与磁体性能的关系;最后指出了纳米复合永磁体目前存在的问题和今后的发展方向。     

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.     

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.     

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.     

Mechanically Driven Alloying and Structural Evolution of Nanocrystalline Fe_(60)Cu_(40) Powder

Highly supersaturated nanocrystalline fcc Fe60Cu40 alloy has been prepared by mechanical alloying of elemental powders. The phase transformation is monitored by X-ray diffraction (XRD),Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS). The powder obtained after milling is of single fcc structure with grain size of nanometer order. The Mossbauer spectra of the milled powder can be fitted by two subspectra whose hyperfine magnetic fields are 16 MA/m and 20 MA/m while that of pure Fe disappeared. EXAFS results show that the radial structure function (RSF) of Fe K-edge changed drastically and finally became similar to that of reference Cu K-edge, while that of Cu K-edge nearly keeps unchanged in the process of milling. These imply that bcc Fe really transforms to fcc structure and alloying between Fe and Cu occurs truly on an atomic scale. EXAFS results indicate that iron atoms tend to segregate at the boundaries and Cu atoms are rich in the fcc lattice. Annealing experiments show that the Fe atoms at the interfaces are easy to cluster to α-Fe at a lower temperature, whereas the iron atoms in the lattice will form γ-Fe first at temperature above 350℃, and then transform to bcc Fe     

Laser/Electron Beam Processing of As-cast Nd_2Fe_(14)B Alloy

It was found that the free Fe in the melted zoneof the as—cast Nd_2Fe_(14)B alloy could be dissolved byIaser/electron beam.The growth direction ofNd_2Fe_(14)B grains is nearly perpendicular to the sur-face of the samples.EDX examination showed thatFe element was homogeneously distributed in themelted zone.Results presented in this paper have giv-en hint to remove free Fe in as—cast Nd_2Fe_(14)B alloy.     

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.     

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).     

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(?)。     

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...