MOSSBAUER STUDIES OF MAGNETIC ANISOTROPY OF AMORPHOUS Fe-(Co, Cr)-Zr ALLOYS

Magnetic anisotropies and hyperfine fields of amorphous a-Fe-(Co, Cr)-Zr alloys, their temperature and thermal stress effects were studied by using a Mossbauer spectroscopy. The results are in the following: A tensile stress field is easily created during the material production process, having the plane anisotropy to be increased for the alloys containing strong ferromagnetic coupling such as Fe-Co and Fe-Ni; a pressure stress field is easily produced, making the perpendicular anisotropy increase for the alloys containing antiferromagnetic coupling such as Fe-Cr and Fe-Mn. Introducing the new idea of attractive and repulsive forces, the fact was explained well that the dependence of anisotropies on the average outer electron concentration of 3d transition metal is similar to that of the average hyperfine field.

ORIGIN OF MAGNETISM STUDY ON SOME COMMERCIAL Fe_2O_3

Six kinds of typical commercial Fe2O3 were sampled and divided into two groups A and B. according to the magnetic measurement results. The samples of group A are of susceptibility about 10-4 and the specific saturation magnetization σs 0.2-0.3 A.M2/kg, being consistent with the feature of antiferromagnetic α-Fe2O3. While the samples of group B display strong magnetism with susceptibility 10-1-10-2 and σs 1.7-12 A.M2 /kg. Mossbauer spectra of the samples were investigated at room temperature in an external magnetic field. It is suggested there is the y - Fe2O3 phase in the group B according to the relative intensities of spectra I(2,5)/I(3,4). This was proved by the Mossbauer spectra for the mixed samples A with γ-Fe2O3 at various contents and by measuring the dependence of specific saturation magnetization on temperature for the samples of group B.

MOSSBAUER STUDY ON MAGNETIC ANISOTROPY OF AMORPHOUS ALLOY Fe_(71)Ni_(10)B_(13)Si_4C_2

Magnetic anisotropies of the amorphous alloy Fe_(71)Ni_(10)B_(13)Si_(14)C_2 annealed in magnetic field have been studied using Mossbauer spectroscopy and X-ray diffraction.It is shown that the distribution of moments in the annealed sample are determined by both stress-produced and thermomagnetic treatment-induced magnetic anisotropies.

MOSSBAUER ANALYSIS ON THE MICROWAVE-MAGNETIC DESULFURIZATION OF RAW COAL

The selective dielectric heating of microwave energy to convert a portion of each pyrite particle to moderately magnetic pyrrhotite has been suggested to enhance the magnetic separation of inorganic sulfur from coal. The results for Mossbauer analyses show that the considerable amount of pyrrhotite produced during microwave irradiation, carrying with it some of non--magnetic pyrite (unconverted), ferrous sulfate, and troilite, is completely removed from coal after magnetic separation. The opthoum desulfurization efficiency can be attsined by appropriately controlling the irradiation time to maximize the amount of pyrrhotite formed pyrite decomposition.Excessive irradiation would be disadvantageous for improving magnetic separation due to the further decomposition of pyrrhotite to antiferromagnetic troilite.

Mossbauer Spectroscopy of Fe-Ni-Nb-B Alloy in Weak Magnetic Field

Amorphous and nanocrystalline (Fe1–xNix)81Nb7B12 (x = 0, 0.25, 0.5, 0.75) alloys were measured by M?ssbauer spectrometry in the weak external magnetic field of 0.5 T. From structural analyses, ferromagnetic bcc-FeNi and fcc-FeNi and paramagnetic (Fe-Ni)23B6 phases were identified in the annealed samples. It was shown that in the external magnetic field the intensities of the 2nd and the 5th lines (A23 parameter) are the most sensitive M?ssbauer parameters. Rather small changes were observed in the values of internal magnetic field. Our results showed that the amorphous precursor is more sensitive to the influence of external magnetic field than the nanocrystalline alloy. All spectra of amorphous precursor showed the increase of A23 parameter and decrease of internal magnetic field values of about 1 T (±0.5 T) under influence of external magnetic field. In the case of nanocrystalline samples the tendency for the values of internal magnetic field is similar but the effect is not so pronounced. The measurements confirmed that even weak external magnetic field affected orientation of the net magnetic moments. Our results indicate that effect of the external magnetic field is stronger in the case of amorphous samples due to their disordered structure.

Mossbauer,X-Ray and Magnetic Studies of Black Sand from the Italian Mediterranean Sea

The study of natural magnetic sands is instrumental to investigate the geological aspects of their formation and of the origin of their territory. In particular, Mossbauer spectroscopy provides unique information on their iron content and on the oxidation state of iron in their mineral composition. The Italian coast on the Mediterranean Sea near Rome is known for the presence of highly magnetic black sands of volcanic origin. A study of the room temperature Mossbauer spectrum, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and magnetic measurements of a sample of black magnetic sand collected on the seashore of the town of Ladispoli is performed. This study reveals magnetite as main constituent with iron in both tetrahedral and octahedral sites. Minor constituents are the iron minerals hematite and ilmenite, the iron containing minerals diopsite, gossular, and allanite, as well as ubiquitous sanidine, quartz, and calcite.

用Mossbauer谱研究Nb对Fe基超微晶软磁合金显微结构的影响

测量制备态和退火态的Ｆｅ７６．５－ｘＣｕ１ＮｂｘＳｉ１３．５Ｂ９（Ｘ＝０、１０、３０、５．２、７．２）合金Ｍｏｓｓｂａｕｅｒ谱结果表明晶化后Ｎｂ、Ｂ等元素向晶界区扩散，在残余非晶中形成了富Ｎｂ、Ｂ区和贫Ｎｂ、Ｂ区Ｎｂ抑制非晶相的晶化和ＦＣ２Ｂ相的析出。

Structure and magnetic properties of Zn ferrite nanoparticles

A series of ZnxFe3-xO4（x = 0, 0. 15, 0. 30, 0o 40, 0. 48, 0. 60, 0. 70 ） nanoparticles prepared by hydrothermal method are studied by use of transmission electron microscope, X-ray diffraction, vibrating sample magnetometer, superconducting quantum interference device magnetometer and Mossbauer spectrometer. All samples present a spinel structure. The lattice constant increases with the increase in the Zn content while the grain size decreases from 18 nm to 9 nm. Moreover, the saturation magnetzafion at 5 K and 293 K increases initially when x ≤ 0. 40 and subsequently decreases when x 〉 0. 40. At room temperature, Mossbauer spectra exhibit a change from a well-defined sextet spectrum to a doublet spectrum as the Zn content increases. The doublet spectrum begins to appear when x = 0. 6, while it begins when x = 0. 80 for the bulk materials. The results of magnetization and Curie temperature measurements indicate that the doublet spectrum is due to the surperparamagnetic state of the nanoparticles. Furthermore, the relationship between the hyperfine field variation and the cation distribution is discussed. The variation of magnetic properties is interpreted by the three-sublattice Yafet-Kittel （Y-K）model.

铁基纳米微晶薄膜巨磁阻抗效应的Mossbauer研究

本文采用 M?ssbauer 谱学方法以及其它手段对 FeCuNbSiB 薄膜样品在退火过程中出现的巨磁阻抗效应发生显著变化的原因进行了探讨。研究表明,样品在退火过程中除了生长纳米晶粒α ? FeSi相对提高材料的软磁性能有利外,同时随退火温度变化样品中磁矩分布方向会发生重取向。由制备态到 570 ℃退火温度期间,薄膜样品磁矩取向发生由平行于平面为主变为垂直为主,而后再转变为平行为主。这些因素对多层膜巨磁阻抗效应的变化会产生重要影响,尤其当磁矩在垂直于平面方向分布占优势时,磁阻抗效应会显著下降。

Bi_2DyFe_5O_（12－x）薄膜的磁性及MOSSBAUER研究

利用Ｘ－射线衍射，磁性测量及测量等手段研究了溅射态氧化物薄膜Ｂｉ＿２ＤｙＦｅ＿５Ｏ＿（１２－ｘ）的结构，磁性及晶化过程，得到了一些新的结果。

用Mossbauer谱探讨甲苯对NdFeB性能的影响

本文利用Ｍｏｓｓｂａｕｅｒ谱和退磁曲线探讨粉末冶金工艺生产的ＮｄＦｅＢ稀土强永磁合金材料的超精细磁场强度，研究在实际生产过程中防氧化保护介质甲苯的含量不同对磁体性能的影响．

BEHAVIORS OF THE HYPERFINE. FIELD AND THE ATOMIC MAGNETIC MOMENT IN AMORPHOUS Fe_(80-x)T_xB_(20)(T=Co,Ni,Mn,V,Ti) ALLOYS

The mean hyper fine field at the Fe nuclei in amorphous alloys Fe80-xTxB20(T=Co,Ni,Mn,V,Ti) by fitting the Moessbauer spectra is displayed. The behaviors of both the hyperfine field and the atomic magnetic moment in these amorphous alloys and the relation between both the properties are discussed.

Structural and Magnetic Analyses of Magnetic Nanoparticles Coated with Oleate Molecules

Physical and chemical properties of the magnetic nanoparticles coated with oleate have been investigated by means of transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Mossbauer spectroscopy, superconducting quantum interference device (SQUID) magnetometry, infrared spectra (IR) and the contact angle device. The results show that doped Al ions in Fe3O4 nanoparticles are located on the octahedral sites of the spinel structure. Oleate is coated on the magnetic nanoparticles with two layers by chemical absorbing, the outer layer can be washed away. The wetting of the surface of magnetic nanoparticles coated with monolayer has been changed from hydrophilicity to hydrophobicity, and the nanoparticles can be dispersed very well in some organic solutions.

Structural, M?ssbauer spectroscopy, magnetic properties, and thermal measurements of Y(3-x)Dy_x Fe_5O_(12)

Yttrium iron garnet powder samples（Y3-xDyxFe5O12）, where part of yttrium ions are substituted by dysprosium ions with different concentrations are prepared by the solid state reaction method. The properties of the prepared samples are examined by different methods such as x-ray diffraction（XRD）, Mssbauer spectroscopy, macroscopic magnetization measurements, and thermal measurements. The XRD measurements show that all the samples reveal the presence of a single garnet phase with a BCC structure. Room temperature Mssbauer spectra indicate that iron ions occupy three magnetic sites, i.e., two octahedral sites and one tetrahedral site. The saturation magnetization and the initial magnetic susceptibility decrease with the increase of Dy^3＋ substitution. The Curie temperature obtained from the thermal measurements seems to be independent of Dy^3＋ substitution.

AN INVESTIGATION OF THE PERMANENT MAGNETS Nd_(15)(Fe, Co)_(77)B_8 WITH Dy AND Al ADDITIVES

Nd-(Fe,Co)-B alloys with Dy and Dy-Al additives have been studied by the Mossbauer effect and X- ray diffraction. The results indicate that the alloys consist of a tetragonal phase, a B-rich phase and a Nd-rich phase. The average magnetic moment of Fe atoms in the tetragonal phase has been determined. The variation of remanence due to Dy and Dy- Al additives has been derived from the Mossbauer data and found to agree with the results of magnetic measurements. The site substitutions of Dy and Al in the alloys are also discussed.

MSSBAUER EFFECT STUDY OF MAGNETIC INTERACTIONS IN Eu(Fe_(0.8)M_(0.2))O_3 (M=Sc, Cr, Mn, Co)

The solid state solutions of europium transition element oxides Eu (Fe0.8M0.2)O3 (M=Sc, Cr, Mn, Co) are synthesized. The X-ray diffraction of the compound shows that all the compounds possess the perovskite structures. Both the 151Eu Mossbauer spectra and the Fe Mossbauer spectra are measured. The hyperfine magnetic field and non-axisymmetric electric field gradient are observed in the Eu Mossbauer spectrum. The 57Fe Mossbauer spectrum shows that there are four components of hyperfine fields corresponding to four kinds of different neighbours of the Fe ion.

MSSBAUER STUDIES ON THE HYDROGEN DECREPITATION AND DESORPTION OF Nd_(16)Fe_(76)B_8 MAGNET

Hydrogen decrepitation and desorption of the Nd16Fe76B8 magnet are studied by X-ray diffraction analysis and Fe Mossbauer spectroscopy. The results of the as-cast alloy samples treated under various hydrogen gas pressures at various temperatures are reported. A special hydrogenation- dehydrogenation treatment of the Nd- Fe- B cast alloy can produce excellent isotropic magnet powders and the treated sample has passed a hydrogenation- disproportion- recombination process. The effect of the presence of α- Fe in magnet powders is discussed.

Mossbauer Measurements of Amorphous Nd-Fe Films

The 57Fe Mossbauer measurements for amorphous NdxFe1-x films (x=0.20-0.40), prepared by flash evaporation with substrate temperature 77K, show a broad hyperfine distribution and it is nearly independent of Nd content x. The effective magnetic moment of Fe atoms in the film is μFe=1.30μB and independent of x within the investigated composition range. The magnetic ordering temperatures Tc deduced from Mossbauer measurements are consistent with those from magnetic measurements under the same conditions (H&rarr0).

Mossbauer Study of Brucite (Mg,Fe)(OH)_2

Mossbauer spectra of brucite mineral from Shanxi in China were measured over a temperature range from 12 K to 500 K. Each spectrum consists of a dominant ferrous doublet and an additional ferric doublet. The most interesting result is the temperature dependence of the line broadenings at T <400 K, with the negative velocity line always more broadened than the positive one. A possible explanation of these systematic broadenings is the presence of a small magnetic perturbation in brucite.

Electromagnetic wave absorbing properties and hyperfine interactions of Fe–Cu–Nb–Si–B nanocomposites

The Fe-Cu-Nb-Si-B alloy nanocomposite containing two ferromagnetic phases （amorphous phase and nanophase phase） is obtained by properly annealing the as-prepared alloys. High resolution transmission electron microscopy （HR- TEM） images show the coexistence of these two phases. It is found that Fe-Si nanograins are surrounded by the retained amorphous ferromagnetic phase. Mossbauer spectroscopy measurements show that the nanophase is the D03-type Fe- Si phase, which is employed to find the atomic fractions of resonant 57Fe atoms in these two phases. The microwave permittivity and permeability spectra of Fe-Cu-Nb-Si-B nanocomposite are measured in the frequency range of 0.5 GHz- 10 GHz. Large relative microwave permeability values are obtained. The results show that the absorber containing the nanocomposite flakes with a volume fraction of 28.59% exhibits good microwave absorption properties. The reflection loss of the absorber is less than -10 dB in a frequency band of 1.93 GHz-3.20 GHz.