Note on the formation and the magnetic properties of amorphous Eu-Ag alloys

Results are reported of an investigation of several amorphous alloys of Eu and Ag made by melt spinning. The crystallization temperatures were determined by differential scanning calorimetry. By means of magnetic measurements it was established that the Eu ions are divalent in all amorphous Eu-Ag alloys. In order to compare the magnetic coupling in the amorphous alloys with that in crystalline compounds, an investigation was also made of the magnetic properties of the compounds Eu₃Si₂ (tetragonal, U₃Si₂-type) and EuAg (orthohombic, FeB-type). Their magnetic properties and lattice constants are given together with those of the compounds EuAg₂ and EuAg₅.     

Magnetic properties of amorphous rare-earth—Iron alloys

The magnetic properties of various amorphous alloys of the type R_1-xFe_x (R = Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu) have been determined in the concentration range 0.3 ? x ? 0.5. With the exception of the Gd and Lu alloys pronounced thermomagnetic history effects were observed in the temperature dependence of the magnetization. These effects are due to a strong temperature dependence of the coercive force (H_c) which is found to obey an exponential law of the form H_c ∞ exp(-αT). ⁵⁷Fe Mössbauer spectra were obtained on the alloys of a composition close to 40 at% Fe. From the combined results of the Mössbauer spectroscopy and magnetic measurements it is derived that the Fe moment decreases if one passes through the rare-earth series. It is postulated that this decrease is due to small differences in the compositional short-range order in the amorphous alloys caused by the heat of mixing becoming more negative in the same sense.     

Resistivity and magnetoresistivity of amorphous rare-earth alloys

The resistivity and magnetoresistivity of amorphous rare-earth alloys are studied starting from the general approach of Van Peski-Tinbergen and Dekker. The random axial crystal-field and the magnetic correlations between the rare-earth ions are consistently taken into account. The characteristic features of the available experimental data are explained both of the case of random ferromagnetic and antiferromagnetic order.     

Stress dependence of the magnetic properties of amorphous Co-Fe-Si-B alloys

For the amorphous alloys Co_75−xFe_xSi₁₅B₁₀ (x = 0, 2, 4, 4.6) and Co₇₅Si₅B₂₀, we have studied the stress depe ndence of the coercive field, the initial susceptibility, the effective anisotropy, and the reduced remanence. The experimental results are in good agreement with a model due to Vázquez, Fernengel and Kronmüller. From our measurements, we obtain the magnetostriction, as well as information about quenched-in stresses and anisotropy mechanisms in these materials.     

Electrical and magnetic properties in Co-P amorphous alloys

Different anomalies in the Hall effect, electrical resistivity, and magnetic susceptibility of simple Co-P amorphous alloys have been observed. We show that the anomalies detected are due to a transition from “para” to “ferromagnetic” order. The transition, which is not well defined, suggests a large compositional inhomogeneity in the samples with high content in P.     

An influence of pressure on magnetic properties of some amorphous alloys

Abstract

The paper presents the results of measurements of of magnetic properties of some Fe based amorphous alloys. The magnetization curves B(H) have been investigated within the range of pressure up to 2.5 GPa showing considerable changes with pressure. The reduction of spontaneous magnetization has been observed due to the pressure shift of Curie temperature. In some cases the total disappearence of ferromagnetism with increase of pressure has been observed at isothermal conditions.     

Magnetostriction and other magnetic properties of Co-Ni based amorphous alloys

The magnetostriction coefficients λ_s of (Co_1−xNi_x)₇₅Si₁₅B₁₀ amorphous alloys have been determined in the range 0 ⩽ x ⩽ 0.41. The dependence of the magnetostriction on temperature T has been related to that of the magnetic polarization J_s in a phenomenological way as λ_s(T) = α[J_s(T)]³ + β[J_s(T)]². The compositional dependence of the coefficients α and β has been obtained.From the studies of the magnetostriction in the region close to the Curie temperature it has been possible to evaluate the magnetostriction critical exponent K.     

Distribution of crystal electric fields in amorphous rare-earth alloys

We report magnetic measurements on extensive series of amorphous alloys containing small concentrations of rare-earths. We find that the magnetic properties of the rare-earth ions are strongly affected by crystal-field effects, particularly for non-Kramers ion such as Pr (J = 4), Tb and Tm (J = 6). Our results cannot be accounted for in models based on simple uniaxial crystal fields. Their analysis in a more general model of quadratic crystal field allows us to derive the distribution of the asymmetry parameter η. Finally we discuss the change of the magnetic behavior and of the local symmetry distribution induced by a structural relaxation of our alloys.     

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.     

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.     

Structure and magnetic properties of iron-and cobalt-based amorphous alloys versus nanocrystallization conditions

The effect of the structural state of Fe₅Co₇₀Si₁₅B₁₀, Fe₆₀Co₂₀Si₅B₁₅, and Co_81.5Mo_9.5Zr₉ amorphous alloys on their magnetic properties is studied under different nanocrystallization conditions. A permanent magnetic field applied during thermomagnetic treatment is found to affect structuring in the amorphous alloys at the initial stage of devitrification. The fine structure of the devitrified amorphous alloys is shown to correlate with the field shifting the hysteresis loop. A mechanism accounting for a hysteresis loop shift in amorphous alloys is discussed.     

Long-term stability of soft magnetic properties of amorphous and nanocrystalline alloys based on iron

In the present paper long-term stability of magnetic properties of different amorphous and nanocrystalline alloys was studied. Magnetic properties were measured for annealed samples (300<Ta<900 K) directly after annealing and after long-term aging at room temperature. It was shown that for the Fe_75.3Cu₁Zr_1.7Si₁₃B₉ alloy magnetic permeability of the optimized samples is stable during 8 years aging. For Fe_86−xNb_xB₁₄ alloys the observed long-term instability (3 years aging) is due to annealing out of free volume leading to formations of small iron clusters coherent with the amorphous surroundings.     

169Tm Mössbauer effect studies of rare-earth amorphous alloys

Tm-M amorphous alloys with M=Cu, Al, Ag, and Fe have been studied using the Mössbauer effect in¹⁶⁹Tm over a temperature range of 0.05 K to room temperature. The spectra for all alloys are strikingly similar, in contrast to those of the crystalline counterparts. The most notable feature of all spectra taken at temperatures below about 30 K is the existence of two distinct subspectra, one with high magnetic hyperfine field that shows no sign of electronic relaxation effects, and the other with low (or zero) field. The origin of the two component subspectra and their temperature dependences is still an open question.     

铁基非晶的低频脉冲磁场处理效应

对非晶合金Fe₇₈ Si₉ B₁₃进行了低频脉冲磁场处理，用穆斯堡尔谱学、透射电 镜等方法观察处理试样的微观结构变化.研究发现，当脉冲频率20—25Hz,磁场16—32kA/m,作用时间≤2min，合金发生了纳米晶化，纳米相岐睩e(Si)晶粒尺寸为10nm. 而且，在低频脉冲磁场处理过程中，非晶试样的温升≤20℃. 关键词： 非晶态合金 脉冲磁场处理 纳米晶化     

Itenerant magnetic properties of amorphous metallic systems: Numerical studies of the Fe-B alloys

A self-consistent method to compute local magnetic moments and spin polarized electron densities of states and to test the stability of the ferromagnetic vs. the paramagnetic state is developed within the framework of the itinerant electron theory. The tight-binding Hamiltonian, with Coulomb correlation among d electrons, is parametrized according to the Slater-Koster interpolation scheme. The method goes beyond the rigid band splitting approximation. We apply it to the Fe_1−xB_x amorphous system for 0 ⩽x⩽0.6 and obtain the magnetization for T=0 as a function of x in agreement with experimental data in the experimentally-accessible concentration region.     

Effects of Mo additions on the glass-forming ability and magnetic properties of bulk amorphous Fe-C-Si-B-P-Mo alloys

Glass formation, mechanical and magnetic properties of the Fe76-xC7.0Si3.3B5.0P8.7Mox (x=0, 1 at.%, 3 at.% and 5 at.%) alloys prepared using an industrial Fe-P master alloy have been studied. With the substitution of Mo for Fe, glass-forming ability (GFA) was significantly enhanced and fully amorphous rods with a diameter of up to 5 mm were produced in the alloy with 3% Mo. The Mo-containing amorphous alloys also exhibited high fracture strength of 3635–3881 MPa and excellent magnetic properties including a high saturation magnetization of 1.10–1.41 T, a high Curie temperature and a low coercive force. The unique combination of high GFA, high fracture strength and excellent magnetic properties make the newly developed bulk metallic glasses viable for practical engineering applications.     

Co-Si-B and Fe-Co-B amorphous alloys: Induced anisotropy and various magnetic properties

The dependence on the metalloid content of some magnetic properties of Co_100−x(Si_0.6B_0.4)_x (22.5 ⩽ x ⩽ 30) and Co₇₅Si_25−xB_x (10 ⩽ x ⩽ 25) amorphous alloys has been studied.Ribbons were subjected to different kinds of heating treatments: field annealing, stress annealing and stress-field annealing (tensile stress and longitudinal magnetic field applied simultaneously). While the anisotropies induced by simple field annealings are of the order of magnitude of 0.1 kJm^-3, the anisotropy induced by stress-field annealing can reach values up to 0.5 kJm^-3. The preferred axis is longitudinal for most of the annealing conditions. The temperature and composition dependence of the magnetostriction have been studied too.Stress, field and stress-field induced anisotropies have also been measured in Co₆₆Fe₉B₂₅ samples (λ_s > 0). In this case the preferred axis is transverse to the ribbon axis.     

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).