Tensile stress dependence of the Curie temperature and hyperfine field in Fe-Zr-B-(Cu) amorphous alloys

Influence of long- and short-range chemical order on spontaneous magnetization in single-crystalline Fe0.6Al0.4compound thin films

We systematically investigate the long- and short-range chemical order, lattice volume, and spontaneous magnetization in single-crystalline Fe0.6Al0.4compound thin films. The vapor-quenching method based on a molecular beam epitaxy technique is utilized to fabricate the single-crystalline Fe0.6Al0.4compound with the differentB2 long-range order parameterS. Swas varied by the deposition temperatureTd,and it increases with increasingTd. The lattice volumeVdecreased with increasingTd, while the tetragonal distortion, ∼4%, due to epitaxial strain were observed. The changes inSandVwere accompanied with the change in the magnetic moment per Fe,μFe.μFeshowed the monotonic decrease as a function ofSwhereasμFemonotonically increases withV. With considering tetragonal distortion,μFe-Vrelationship has a good agreement with the previous reports. TheμFe-Srelationship showed the steep decrease ofμFearoundS∼ 0.6. In contrast toμFe-Vrelationship,μFe-Srelationship does not match only from ours to previous studies but also among other reports. It implies the statistical number of the nearest-neighbor Fe-Fe bonds, i.e.S, cannot be an enough explanatory parameter. To clarify the structural origin of change inμFe, the short-range order (SRO) parameter inferred from the analysis of superlattice diffractions were introduced. They showed the clear difference for the films with high and lowμFe. The results suggest that the transition from the long- to the SRO state plays the significant role onμFe.

Unveiling the local structure of the amorphous metal [Formula: see text] combining first-principles-based simulations and modelling of EXAFS spectra

Amorphous alloys exhibit useful properties such as the excellent soft magnetic behaviour of Fe-based metallic glasses. The detailed structure of amorphous [Formula: see text] with x = 0.07, 0.10, and 0.20 is in this work explored through a synergetic combination of atomistic simulations and experimental characterisation. Thin-film samples were investigated using X-ray diffraction and extended X-ray absorption fine structure (EXAFS), while the corresponding atomic structures were simulated using an efficient first-principles-based method called stochastic quenching (SQ). The simulated local atomic arrangements are investigated by constructing the radial- and angular-distribution functions, as well as by Voronoi tesselation. The radial distribution functions are then used to construct a model to fit simultaneously the experimental EXAFS data of multiple samples with different compositions, creating a simple yet accurate description of the atomic structures valid for any composition in the range x = 0.07 to 0.20, using a minimal number of free parameters. This approach significantly improves the accuracy of the fitted parameters and allows us to relate the compositional dependence of the amorphous structures with the magnetic properties. The proposed EXAFS fitting process can be generalised to other amorphous systems, contributing to the understanding of structure-property relationships and the development of amorphous alloys with tailored functional properties.

The Influence of Boron on Microstructural Evolution, Mechanical and Magnetic Behavior of Amorphous Fe91−x(Zr5-Nb4)Bx Melt-Spun Alloys

In this work, we report a systematic study on the microstructure evolution of rapid solidified Fe91−xZr5Nb4Bx alloys (x = 10, 15, 20, 25, 30 at%) under melt-spinning conditions. Mechanical and magnetic properties are also evaluated. X-ray diffraction patterns indicate that the microstructure across the compositional series consists of an amorphous matrix with partial crystallization when boron concentration is increased. These features were identified by transmission electron microscopy (TEM). The radial distribution function (RDF) affords to resolve the nearest-neighbor configuration. The tensile and microhardness properties were measured to correlate the microstructural evolution with boron content. On the other hand, the magnetic properties of these alloy series were determined by vibrating sample magnetometry (VSM); the saturation magnetization and Curie temperature showed an increasing tendency when increasing the boron content, reaching values up to 110 Am2kg−1 and 465 K, respectively. In addition to the aforementioned, the coercive field remained constant. All these magnetic properties were correlated with the microstructure features observed by XRD, RDF and TEM.

Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent 'Stoner type' magnetization for the amorphous alloys in contrast to 'Heisenberg type' in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

Pressure dependence of magnetic properties in Fe-Mn-B amorphous alloys: evidence for inhomogeneous ferromagnetism

The pressure dependence of the saturation magnetization and Curie temperature was studied in melt-spun Fe60Mn20B20, Fe56Mn24B20 and Fe75B25 amorphous alloys up to 0.9 GPa, corresponding to volume changes up to 0.45%. In addition, in situ high-pressure (up to 40 GPa) x-ray diffraction was performed to determine the compressibility of the latter two alloys. Both the Curie temperature TC (at atmospheric pressure TC = 201 ± 3 and 159 ± 3 K) and the low-temperature saturation magnetization M5 K,5 T decrease remarkably with increasing pressure: dTC/dp =- 31 ± 0.5 and -32 ± 5 K GPa(-1) and dlnM5 K,5 T/dp =- 0.15 ± 0.02 and -0.13 ± 0.03 GPa(-1) for xMn = 20 and 24 at.%, respectively. Compared to dlnM5 K,5 T/dp =- 0.016 ± 0.003 GPa(-1) measured for Fe75B25, the pressure dependence of M5 K,5 T is one order of magnitude larger in the ternary alloys. The bulk moduli for the Fe56Mn24B20 and Fe75B25 glasses were measured to be 152 GPa and 173 GPa, respectively. These data are also compared with the pressure dependence of the hyperfine field and theoretical calculations of the saturation moment for Fe-B alloys reported in the literature. The results were interpreted within an inhomogeneous itinerant-electron model of ferromagnetism.

Magnetization Dynamics of Amorphous Ribbons and Wires Studied by Inductance Spectroscopy

Inductance spectroscopy is a particular formulation variant of the well known complex impedance formalism typically used for the electric characterization of dielectric, ferroelectric, and piezoelectric materials. It has been successfully exploited as a versatile tool for characterization of the magnetization dynamics in amorphous ribbons and wires by means of simple experiments involving coils for sample holding and impedance analyzer equipment. This technique affords the resolution of the magnetization processes in soft magnetic materials, in terms of reversible deformation of pinned domain walls, domain wall displacements and spin rotation, for which characteristic parameters such as the alloy initial permeability and the relaxation frequencies, indicating the dispersion of each process, can be defined. Additionally, these parameters can be correlated with chemical composition variation, size effects and induced anisotropies, leading to a more physical insight for the understanding of the frequency dependent magnetic response of amorphous alloys, which is of prime interest for the development of novel applications in the field of telecommunication and sensing technologies. In this work, a brief overview, together with recent progress on the magnetization dynamics of amorphous ribbons, wires, microwires and biphase wires, is presented and discussed for the intermediate frequency interval between 10 Hz and 13 MHz.