非晶Fe89.7 P10.3合金纳米线阵列的磁性研究

利用电化学沉积方法在阳极氧化铝模板中制备了Fe89.7P10.3非晶合金纳米线阵列.利用x射线衍射仪、透射电子显微镜、振动样品磁强计和穆斯堡尔谱仪研究了样品的结构和磁性,发现纳米线阵列是非晶结构,且拥有垂直磁各向异性和高的矫顽力,Hc=3.04×104A/m.纳米线内部的平均超精细场和平均同质异能移分别为2.15×106 A/m和0.07 mm/s;而纳米线末端的平均超精细场(2.33×106A/m)大于内部的值,平均同质异能移(0.04mm/s)小于内部的值.另外,纳米线内部Fe原子磁矩与线轴的夹角约为16°,而在纳米线末端Fe原子磁矩与线轴的夹角约为28°.这些结果表明,由于形状各向异性,在纳米线中实现了无序非晶合金磁矩的有序排列.     

Sputtered ductile amorphous Fe80B20 foils

Ductile amorphous foils of Fe₈₀B₂₀ have been sputter-deposited. We report here the results of structural and magnetic studies on these samples. Structural analysis shows slight differences between amorphous foils and ribbons. From the high-field measurements (H<15 T) the magnetic moment of Fe is estimated as 2.1±0.02 at 4.2 K in agreement with the value reported for ribbons. However, the magnetization is less temperature dependent in the foil, as compared to the ribbon. This result would indicate a lesser fluctuation in the exchange integralJ and hence lesser variations in the local environment of Fe. Finally the thermal stability is shown to be higher in the foils. It is suggested that sputtering technique could be used to prepare amorphous foils of large area for certain applications.     

Magnetic properties of lithographically defined lateral Co/Ni80Fe20 wires

A novel micro-fabrication technique has been used to create an array of lateral magnetic multilayers consisting of micron-sized sputtered Co and Ni₈₀Fe₂₀ wires. The structures were fabricated using conventional optical lithography and a combination of hard and soft lift-off methods. For the field applied parallel to the wires intrinsic easy axis, we observed two switching fields corresponding to the distinct coercive field of the Ni₈₀Fe₂₀ wires (H_c1) and Co wires (H_c2) constituting the lateral multilayer wire array. A state of anti-parallel relative alignment of magnetization was observed when the applied field is greater than the switching field of Ni₈₀Fe₂₀ wires but less than the switching field of Co wires. We found the region of anti-parallel alignment of magnetization between the Co and Ni₈₀Fe₂₀ wires to be very sensitive to the relative orientation of the applied magnetic field.     

Surface characterization of amorphous and crystallized Fe80B20

Recent studies of catalysis by amorphous metals have prompted an interest in their surface properties. We have utilized Auger electron spectroscopy, X-ray photoelectron spectroscopy and low energy alkali ion scattering to study the surface composition, electronic properties and topography of amorphous and crystallized Fe₈₀B₂₀ ribbons. The majorresults are that the surface stoichiometry is approximately that of the bulk, unaltered by segregation. Bulk crystallization results in the diffusion of impurities to the surface, but does not change the Fe/B ratio. A small shift in the B1s core level binding energy was observed on crystalline, annealed surfaces relative to amorphous or sputtered surfaces, but no shifts were observed in the iron core level energies. A weak feature due to the B2p levels was observed in the valence band spectra from sputtered surfaces. The surfaces exhibit atomic scale roughness which is not altered by bulk crystallization. Finally, there were no observable differences in the structure, composition or electronic properties between the two sides of the ribbons.     

Magnetic properties of metallic glasses of the type Fe80−x Pd x B20 and Fe80−x Pt x B20

Amorphous alloys of the type Fe_80???xPd_xB₂₀ and type Fe_80???xPt_xB₂₀ for 0?≤?x?≤?50 have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy and magnetisation measurements in temperatures from 4.2 up to 300 K. Curie temperatures and crystallisation temperatures are found by DTMG-DTA method. Mössbauer spectroscopy magnetic field is observed to visible increase for x?=?1 and 1.5% at room temperature for Pd, while a decrease is observed for higher x values. Curie temperature for Pd alloys has a maximum at x?=?4 with T _C?=?753 K, which supports enforcing influence of Pd at low concentrations of Pd for magnetic interactions. We discuss different explanations for these measurements and compare with other findings for high Pd concentrations and alloys with Pt instead of Pd.     

Magnetic clusters in amorphous Fe90Sc10 alloy

In order to obtain information on the nature of spin coupling in Fe-rich alloys, we performed high-precision⁵⁷Fe Mössbauer effect and magnetizations measurements in a wide temperature range. These results show that with increasing temperature amorphous Fe₉₀Sc₁₀ alloys undergo a transition from a cluster spin-glass to superparamagnetism followed by paramagnetism.     

EXAFS study of the atomic structure of amorphous Tb20Fe80

The atomic structure of amorphous Tb₂₀Fe₈₀ thin films has been studied by Extended X-ray Absorption Fine Structure (EXAFS) of both FeK and TbL _III absorption edges. The local site geometry around Fe atoms shows predominantly Fe nearest neighbors with an Fe-Fe distance distribution centered on 2.50±0.02 Å and a coordination number of 9.1±1. In contrast, the radial structure function (RSF) obtained at the Tb edge is broad and asymmetric. The peak in the RSF corresponds to a Tb-Fe near neighbor distance of 2.94±0.1 Å with no evidence for Tb-Tb nearest neighbor coordination. The width and the shape of the RSF suggest that the Tb-Fe atomic environment is anisotropic and strained probably as a consequence of the growth process. This distorted atomic environment is suggested to be responsible for the magnetic anisotropy in these alloys. Thermal annealing at 200 °C leads to reduction inK _u. We propose that this results from reordering of the Tb local environment such that the average structural anisotropy in the distribution is reduced. EXAFS data show that annealing at 400°C causes precipitation of bcc polycrystalline Fe. The addition of 7 at.% Au to the alloy prevents this recrystallization and preserves the amorphous state but does not prevent the structural relaxation which reducesK _u at lower temperatures.     

Mössbauer spectroscopy of amorphous metglass Fe80B20

Amorphous metals (Metglass Fe₈₀B₂₀) have been studied by Mössbauer spectroscopy. In the analysis the radial distribution function of Bernal's liquid-structure model has been correlated with the distribution of magnetic hyperfine spectra.     

Study of the structural relaxation and crystallization in amorphous Fe80P20 alloy by mössbauer effect

The structural relaxation and crystallization of amorphous Fe₈₀P₂₀ alloys have been investigated by Mössbauer spectroscopy. The result indicates that the process of the crystallization of Fe₈₀P₂₀ makes slow progress and it was occur from outside into inside. The amorphous alloys may be classified into six different stages from amorphous to crystalline state during annealing.     

Magnetic properties of amorphous Ge–Fe thin films

Thin films of Ge_100−xFe_x (x in at%) alloys, fabricated by thermal co-evaporation, have an amorphous structure at compositions x<∼40, although an unidentified crystalline phase with an FCC symmetry also exists at low Fe content. Magnetization versus temperature curves show that saturation magnetization is non-zero (1 to 2.5 emu/cm³) and remains nearly unchanged up to the highest measured temperature of 350 K. Magnetic hysteresis loops at room temperature show a typical ferromagnetic shape, complete saturation occurring by 1–2 kOe. These results may indicate ferromagnetic ordering at room temperature. No definite tendency is observed in the compositional dependence of saturation magnetization.     

PES study of amorphous alloy Fe40Ni40P20

The electron structure of amorphous Fe₄₀NI₄₀P₂₀ has been investigated before and after annealing by XPS and UPS (HeI, HeII). It is shown that the spectra of UPS were modified obviously by various degree of annealing. Composition and chemical states of the components on the surface of the sample are also presented and the effect of structural ordering on the density of states (DOS) of the valence band is discussed.     

退火诱导亚稳态Fe80Cu20合金固溶体的结构相变

利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe80Cu20合金固溶体的结构随退火温度的变化特点.结果表明,在300-873 K温度范围内,随着退火温度的升高,bcc结构物相的晶格常数近于线性降低,这主要是由于Cu原子从bcc结构Fe80Cu20合金固溶体中逐渐偏析出来,生成面心立方(fcc)结构的Cu物相所致.经603 K退火后,Cu原子的平均键长RCu-Cu增加了0.003 nm左右,大约有50%的Cu原子从bcc结构的Fe80Cu20合金固溶体中偏析出来.在773 K退火后,bcc结构Fe80Cu20合金固溶体近于完全相分离,生成了bcc结构的α-Fe与fcc结构的Cu物相.     

Structure of amorphous Fe80-P13-C7 alloy by X-ray diffraction

In the frame of a semiclassical picture a systematic approximation scheme for the hopping-conductivity is derived which provides a classification in terms of the length of correlated hopping-chains. With the aid of an integral equation for the propagation probability of carriers and a decoupling procedure for configuration averages, conductivity is expressed by the zeroth and second moments of independently averaged contributions of paths containing less than a fixed number of hops. A sum rule allows to carry out the static limit explicitly. The lowest order conductivity reduces to a simple form which is presented for later evaluations.     

Structural relaxation effects on the hyperfine parameters in Fe80B20 amorphous alloys

We have studied the influence of the relaxation effects on the different kinds of short range order structures which can be distinguished inFe ₈₀ B ₂₀ amorphous alloys by Mössbauer spectroscopy. The analysis of the distribution function of the hyperfine fields gives results on the variations of the chemical and topological short-range orders in good agreement with those known in literature. Attempt to give quantitative results is made.     

Magnetic interaction between ultrafine amorphous Fe1-xCx alloy particles in ferrofluids

Ferrofluids with ultrafine magnetic particles of amorphous Fe_1-xC_x were studied by Mössbauer spectroscopy, transmission electron microscopy and magnetic measurements. Magnetic measurements showed that the initial susceptibility follows a Curie-Weiss law, indicating magnetic interaction between the particles. The influence of the magnetic interaction on the estimation of the particle size, made from the field dependence of the induced hyperfine splitting, is discussed.     

Diffusion of Au and Cu in amorphous Fe80B20 and Fe82B18 alloys

Diffusion rates (D) of Au in two amorphous alloys, Fe₈₀B₂₀ and Fe₈₂B₁₈, and of Cu in amorphous Fe₈₂B₁₈ alloy were measured in the temperature range 546–645 K by using the technique of Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES), respectively. The diffusion of Au was found to be 3 to 6 times faster in Fe₈₀B₂₀ than in Fe₈₂B₁₈, though both the alloys had almost similar crystallization temperatures. The observed differences in the diffusion rates corroborate the fact that Fe₈₀B₂₀ has a more open structure than Fe₈₂B₁₈ as revealed from the reported values of the metal packing fractions of these two alloys. Also, the diffusivities of smaller sized Cu atoms (radius: 0.128 nm) were found to be higher by more than an order of magnitude than those of larger sized Au atoms (radius: 0.146 nm), suggesting a dependence ofD on the size of the diffusing species.