Influence of structural relaxation on the magnetic permeability aftereffect of amorphous ferromagnetic alloys

Room temperature measurements of the aftereffect of the magnetic permeability have been performed on amorphous Fe-(Cu--Cr)-B ribbons annealed at various temperatures. The results, in good agreement with the predictions of a new theory, give information on the effect of structural relaxation on the shear stress defects responsible for the magnetic aftereffect.     

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.     

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.     

Weak ferromagnetic properties of amorphous FeGe alloys

Magnetization measurements of amorphous FeGe alloys containing 20 and 30 at.% iron have been made under high field and high pressure. These alloys possess a weakly itinerant ferromagnetic character although large inhomogeneous effects are superposed.     

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.     

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.     

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.     

Unified analysis of diffusion and relaxation processes in amorphous metallic alloys

Abstract

Self-diffusion data on amorphous metallic alloys determined in long-time radio-tracer experiments and activation-enthalpy spectra deduced from short-time structural relaxation studies on such materials are reviewed and analyzed in terms of current random transition rate models. It is shown that the seeming discrepancy between the self-diffusion enthalpies and the comparatively small enthalpies obtained from measurements of the magnetic after-effect arises from the existence of activation-enthalpy spectra. Whereas the short-time experiments reveal the small-activation-enthalpy parts of these spectra, the long-time self-diffusion experiments are controlled by the larger activation enthalpies. Assuming that the activation-enthalpy distributions are Gaussian, their characteristic parameters have been determined by comparing the two types of measurements. It is shown that the Arrhenius-type diffusion coefficients found by experiment are compatible with half-widths of the activation-enthalpy spectra of about 0.3 eV. Based on an analysis of the pre-exponential factors and other typical properties of the diffusion coefficients, potential mechanisms of the diffusion in amorphous alloys are proposed.     

Comparison of a fractal analysis and debye relaxation for the structural relaxation in amorphous metals

Abstract

Magnetic After-Effect isotherms have been measured on a metallic glass pre-annealed for different times. The results have been analyzed simultaneously by Debye relaxation functions leading to spectra of activation enthalpies and by extended exponential functions leading to a unique effective activation enthalpy. The thermodynamic activation parameters issued from both analyses compare well. The average values of the enthalpy spectra determined by assuming Debye relaxations are equal to the effective enthalpies resulting from the non-Debye relaxation.

Magnetische Nachwirkungs-Isothermen wurden an amorphen Legierungen gemessen, die mit verschiedenen Anlasszeiten vorbehandelt wurden. Die Ergebnisse wurden sowohl unter der Annahme von Debye-Relaxationsprozessen analysiert, die mit Aktivierungsspektren beschrieben wurden, als auch mit gestreckten Exponentialfunktionen, die zu einer einheitlichen effektiven Aktivierungsenthalpie führt. Die thermodynamischen Parameter von beiden Analysen sind gut vergleichbar. Die Mittelwerte der Aktivierungsenthalpie-Spektren, welche sich bei Zugrundelegung der Debye-Relaxationsprozesse ergeben, entsprechen den effektiven Enthalpien, die sich bei Anwendung der gestreckten Exponentialfunktionen ergeben.

Des isothermes de trainage magnétique ont été réalisées sur des echantillons de verres métalliques ayant subi des traitements thermiques de différentes durées. Les résultats ont été simultanément analysés par des processus de relaxation de Debye engendrant des distributions d'enthalpies d'activation, et par des exponentielles etirées possédant des enthalpies effectives. Les paramètres thermodynamiques issus des deux analyses sont cohérents et comparables. Les valeurs moyennes des distributions d'enthalpies résultant de la relaxation de Debye sont identiques aux enthalpies effectives qui découlent des exponentielles etirées.     

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.     

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.     

Magnetic phases of amorphous transition metal-metalloid alloys

Hysteresis loop and ac susceptibility measurements were performed on three series of amorphous alloys: (A_wB_1-w)₇₅P₁₆B₆Al₃, where (A, B) are (Fe, Ni), (Co, Ni) and (Fe, Mn). Upon cooling, low w alloys undergo paramagne t to spin glass transitions. Alloys with higher w first experience a Curie transition to a ferromagnetic state, and then a spin freezing transition to a spin glass state. the T dependence of the width of the ac hysteresis loop is used to determine the spin freezing transition temperature. A magnetic phase diagram is presented for each alloy series and the value of w required for ferromagnetism, w_C, is determined. When measured in the presence of small constant fields, the ac susceptibility of alloys with w just above w_C has maxima near both transition temperatures. The field and temperature dependences of the peaks are explained by scaling arguments, used to determine the critical exponent δ for the Curie transition, and suggest that a similar scaling law holds for the ferromagnet to spin glass transition.     

Superconducting properties of amorphous transition metal alloys

We have co-sputtered amorphous films of several Mo and W-based superconducting alloys. Measurements of T_c, ($\text{d}\text{H}{}_{\mathrm{c2}}\text{d}\text{T}$)_Tc and the normal state resistivity near T_c were made on a number of these alloys. Our results and other data from the literature are studied to examine the correlation between T_c and the dressed density of states at the Fermi level.     

Electronic structure of amorphous transition metal alloys

The electrical resistivity, the Hall coefficient and the magnetic susceptibility of amorphous alloys (Metglass 2826A, Allied Chemical) have been measured above room temperature. The experimental data show strong similarities with liquid alloys.     

Thermoelectric power of amorphous alloys near the metal-insulator transition

The thermoolectric powerS and the electrical conductivity σ of amorphous Au_xSb_100-x and Cu_xSb_100-x films have been measured in the temperature range between about 2 K and 350 K for concentrations close to the eetal-insulator transition. In both systems the transition occurs at a critical concentrationx _c≈8 at.% noble metal content. A characteristic feature of the transition is in both cases a strong increase of the low temperature slope of the thermopower, i.e.S/T| _t»0 , when approachingx _c from the metallic side. The results are compared with different theoretical predictions for the metal-insulator transition. Furthermore we report on the changes ofS and σ during annelaing. It will be shown that especiallyS(T) of the samples withx close tox _c depends strongly on the annealing state of the films.     

Magnetovolume effect in transition metal-metalloid amorphous alloys

The thermal expansion, spontaneous volume magnetostriction ω_s, forced volume magnetostriction $\text{(}\text{?ω}\text{?H}\text{)}$ and Young's modulus of amorphous Fe-B, Fe-P, Co-B and (Fe-M)₇₇Si₁₀B₁₃ (M = Cr, Mn, Co, Ni) alloys have been measured to make clear the magnetovolume effect in transition metal-metalloid amorphous alloys. The thermal expansion coefficient α, ω_s and $\text{(}\text{?ω}\text{?H}\text{)}$ are dependent on the number of d-electrons per transition metal atom n_eff calculated based on the charge transfer model. The n_eff vs. α, ω_s and $\text{(}\text{?ω}\text{?H}\text{)}$ curves are quite similar to the corresponding curves in fcc alloys. The maxima in those curves are, however, found at n_eff ≈ 8.2 for the amorphous alloys in contrast with n_eff ≈ 8.7 for the fcc Fe-Ni alloys. On the other hand, Young's modulus measured under the saturation of magnetization is governed by the molar volume, irrespective of n_eff. The magnetovolume effect in transition metal-metalloid amorphous alloys is discussed in connection with the instability of ferromagnetism of amorphous Fe.