Short range order in amorphous FeGe alloys

The short range order in Fe_xGe_1-x amorphous alloys is analysed by use of electron diffraction diagrams. It is shown that the number of nearest neighbours increases from a value of 4 when x equals zero to a value of 9 for x ≥ 0.47. It is suggested that hybridization between the sp states of germanium and the d states of iron plays an important role in stabilizing the high coordination amorphous phase found in the alloys with high content of iron.     

Invar-type new ferromagnetic amorphous Fe-B alloys

Measurements of magnetization, electrical resistivity, thermal expansion and differential thermal change were made on amorphous Fe_100-xB_x (9 ≦ X ≦ 21) alloys prepared by rapid quenching from the liquid state.With decreasing boron content in the alloys, the Curie temperature falls remarkably, while the magnetic moment increases sluggishly. The thermal expansion curves exhibit the invar characteristics below the Curie temperature due to a large positive spontaneous volume magnetostriction, and the reduced magnetization curves decrease much more rapidly with increasing temperature than those of other ferromagnetic amorphous alloys.     

Short-range order in amorphous ferromagnetic Fe-B alloys

Amorphous and quenched crystalline Fe-B alloys in the composition range of 4–25 at % B were prepared by melt spinning and investigated by ⁵⁷Fe Mössbauer spectroscopy at T = 87 K. The states of iron atoms in the α-Fe phases, including iron atoms having boron atoms in the nearest coordination sphere, and in the orthorhombic (o) and tetragonal (T) Fe₂B phases are detected in the microcrystalline alloys. The short-range order and the local atomic structure of the amorphous Fe-B alloys are determined. The amorphous alloys consist of microregions (clusters) with short-range order of the t- and o-Fe₂B and α-Fe types. The dependence of the content of various types of clusters on the alloy composition is quantitatively estimated.     

源于非晶合金的透明磁性半导体

磁性半导体兼具磁性和半导体特性,通过操控电子自旋,有望实现接近完全的电子极化,提供一种全新的导电方式和器件概念.目前磁性半导体的研究对象主要为稀磁半导体,采用在非磁性半导体中添加过渡族磁性元素使半导体获得内禀磁性的方法进行制备.但大部分稀磁半导体仅具有低温磁性,成为限制其在室温可操控电子器件中应用的瓶颈.针对这一关键科学问题,本文提出与传统稀磁半导体制备方法相反的合成思路,在磁性非晶合金中引入非金属元素诱发金属-半导体转变,使磁性非晶获得半导体电性,研制出具有新奇磁、光、电耦合特性的非晶态浓磁半导体,揭示其载流子调制磁性的内禀机理,发展出可在室温下工作的p-n结及电控磁器件.     

On the resistivity minimum in amorphous ferromagnetic alloys

We present a theoretical approach which, taking into account the amorphous nature of the system and the correlations between nearest-neighbour magnetic ions, gives a plausible explanation of some features present in the electrical resistivity of amorphous ferromagnetic alloys with transition metals.     

Effect of electric current on the magnetic and magnetoelastic properties of amorphous ferromagnetic alloys

The magnetic and magnetoelastic parameters of Fe₆₄Co₂₁B₁₅ and Fe_81.5B_13.5Si₃C₂ amorphous ferromagnetic alloys treated by direct electric current in air are studied as functions of the applied magnetic field and current density. The samples of the alloy have the form of narrow strips with different lengths. It is found that the magnetoelastic parameters of the dc-treated alloys depend on the magnetic field in a qualitatively different way. From the behavior of the magnetic and magnetoelastic parameters of the alloys in the magnetic field a model of magnetization nonuniform distribution in amorphous ferromagnetic alloys subjected to dc treatment is proposed.     

Theory of the coercive field in amorphous ferromagnetic alloys

The coercive field of amorphous ferromagnetic alloys is determined by defect structures, surface irregularities, relaxation phenomena and intrinsic fluctuations of the material properties. Within the framework of micromagnetism these different contributions are determined quantitatively. It is shown that in magnetostrictive alloys defect structures are dominant whereas in non-magnetostrictive materials surface irregularities and relaxation effects become important.     

Magnetic properties of amorphous alloys

The magnetic properties of existing amorphous iron based materials, i.e., Fe--metalloid, Fe--early transition metals and Fe--rare earth alloys, are briefly discussed for some representative alloys. The spin orientation of amorphous Fe--metalloid alloys has been determined by the angular dependence of hyperfine interactions. It is shown that in iron--early transition metals ferromagnetic order is not long-ranged, but determined by magnetic clusters. The magnetic hyperfine field distributions of Fe-rich iron--early transition metals consist of a high and a low field tail. The magnetic structure has been investigated for two representative Fe--RE (RE = Er, Ce) amorphous alloys. For the first time, the magnetic coupling phenomenon in amorphous/crystalline multilayers has been discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Continuous versus discrete hyperfine-field distributions in amorphous ferromagnetic iron alloys

The Mössbauer spectra of amorphous alloys possess broad absorption lines which are usually attributed to a continuous hyperfine-field distribution. The analysis of such spectra can be made simpler and less ambiguous by eliminating the second and fifth lines (the Δm_I = 0 transitions). By applying a large external magnetic field parallel to the propagation direction of the γ-ray, four-line Mössbauer spectra have been obtained for amorphous Fe₇₈B₁₂Si₁₀ and Fe₄₀Ni₄₀P₁₄B₆ (METGLAS® 2826). A discrete hyperfine-field distribution based on Bernal's liquid-structure model fits the data well. Other aspects of the results are discussed.     

Effect of pressure oh the ferromagnetic transition of Fe-Ni-Cr-Mo-B-Si amorphous alloys

Pressure effects on the Curie temperature in FeNiCrMoSiB amorphous alloys are discussed in terms of the Wagner and Wohlfarth theory for magnetic inhomogeneous states.The authors wish to thank Dr.P.Duhaj of the Institute of Physics, Slovak Acad.Sci., for supplying the amorphous alloys examined in the present study.     

Distribution of dipole fields in disordered crystalline and amorphous ferromagnetic alloys

By means of computer simulation we have calculated the distribution functions of dipole fields in disordered crystalline and amorphous ferromagnetic alloys A_1-xB_x. It is shown that for all cubic lattice sites in simple cubic, body-centred cubic and face-centred cubic materials as well as for amorphous materials the envelopes of the distribution functions may be obtained in a satisfactory approximation by considering only the nearest contributing atoms. Whereas in crystalline materials we have a complicated structure of the distribution functions for arbitrary values ofx, we obtain simple Gaussian distributions for the case of amorphous materials, using Heimendahl's model of the amorphous structure. The influence of isotropic and anisotropic short-range order is discussed in detail.     

Reappraisal of the published neutron diffraction data on amorphous ferromagnetic alloys

A reanalysis of the previously reported neutron diffraction data on glassy ferromagnetic alloys suggest that the spin-wave energies of some glasses renormalize in accordance with the predictions of the itinerant-electron model. This observation is shown to have a direct bearing on the discrepancy between the spin-wave stiffness coefficient values D_s (neutron diffraction) and D_m (magnetization) found in certain amorphous ferromagnets.     

Mössbauer studies of moment distribution in amorphous ferromagnetic alloys

A spin spatial distribution in terms of an expansion in spherical harmonics containing deviation parameters from the symmetry axis P (0, ?) is used to describe the moment distribution of amorphous ribbon alloys. According to the theoretical analysis and Mössbauer measurement, P (0, ?) values and squareness S_xy (0, ?) and S_z can be obtained. The P (0, ?) distribution of FeNiSiBC and hydrided FeCrSiB amorphous alloys are studied.     

Magnetization processes in the narrow domain structures of amorphous ferromagnetic alloys

The magnetization processes within the narrow domain laminae of amorphous ferromagnetic alloys have been investigated by means of the magneto-optical Kerr effect. Changes of the domain width of the closure domains by a magnetic field applied perpendicular to the laminae have been determined for the alloys Fe₈₀B₂₀ and Fe₄₀Ni₄₀P₁₄B₆. These results are compared with theoretical calculations, assuming that wall displacements within the closure domains and rotations of the magnetization in the bulk domains take place simultaneously and a stray field free domain structure is developed. It turned out, that the closure domain structure on the surface of the sample vanishes at the same magnetic field where magnetic saturation is approached.     

Magnetic properties of amorphous NiP alloys

Magnetization, NMR and coercive force measurements were performed on amorphous Ni_1?cP_c alloys for concentration ranging between 0.15 and 0.25. The experimental results show that the magnetism is not of the same nature below and above some critical concentration c₀ which determines the concentration ranges: the first one (0.15 < c < 0.18) presents the characters of a weak homogeneous ferromagnetism, while inhomogeneities dominate the magnetic properties of the second one (0.18 < c < 0.25).     

Mechanical properties of Co-Si-B amorphous alloys

The ternary amorphous systems Co_xSi₅B_95?x with 7070Si _y B_30?y with 5<y<18 were studied for their mechanical properties at room temperature. Structure sensitive parameters as density, Young's modulus, micro-hardness and crystallization temperature were investigated as a function of Co and Si contents. The value of density increases with higher Co content but not linearly as for Co-B. Young's modulus, micro-hardness and crystallization temperature decrease with increasing Co concentration. The packing fractionη was calculated using 12-coordinated Goldschmidt atomic radii. It is shown that changes in the proportions of metalloids contents in the alloys have more significant influence on the atomic structure and therefore on the mechanical properties than changes of Co content. The maximum tensile elastic strain for the Co-Si-B system was estimated. Influence of magnetic moment on Young's modulus is discussed.     

Magnetic properties for heterogeneous weakly ferromagnetic alloys

Using the Landau theory of phase transitions, Arrott plots, the high field and the paramagnetic susceptibility and the magnetization of heterogeneous weakly ferromagnetic alloys are calculated analytically for a simple model for the heterogeneity.     

The microwave resonance line shape in ferromagnetic cubic FeGe

The ferromagnetic resonance as well as the antiresonance in cubic FeGe have been studied in the temperature range 77–300 K using the frequencies 9·5 and 35 GHz. The observed line broadening was found to be due to the shape of the samples. Experimentally determined values are given for saturation magnetizations, g-factors and demagnetization factors. The latter differ considerably from those calculated in the ellipsoidal approximation. The g-factor increases from 2·07 at 35 GHz to 2·18 at 9·5 GHz. The line shape of the magnetic resonances has been calculated for an external magnetic field parallel as well as perpendicular to the plane of a disc-shaped sample. The calculations are outlined in the paper and the results are presented in the form of the derivatives of the calculated spectra. The latter are found to be in excellent agreement with experimental results. Exchange and spin pinning turned out to have negligible influence on the lines. The theoretical results have been obtained from the perturbation theory of Lax and Button which was modified by augmenting the dynamic susceptibility with a constant in order to account for the behavior of the cavity fields at the walls.