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• Fe 84 Zr x B 16- x (x = 6, 8, and 10 at. %) alloys show pronounced β relaxation characteristic. • A positive correlation between the β relaxation and structural heterogeneity appears in Fe-based amorphous alloys. • With increased Zr/B ratio, β relaxation is easily activated and structure becomes more heterogeneous. • Alloys with easily activated β relaxation or more heterogeneous structure possess poor soft magnetic properties. Dynamic relaxation is an universal feature in amorphous alloys. However, few studies have been conducted on β relaxation of Fe-based amorphous alloys as most of them have insignificant β relaxation characteristics. In this work, the variation in β relaxation, structural heterogeneity, and soft magnetic properties are investigated in Fe-Zr-B amorphous alloys with pronounced β relaxation. β relaxation and structural heterogeneity are characterized by the ratio of β and α relaxation temperature (i.e., T β /T α) and correlation length, respectively. With the increase of Zr/B ratio, the value of T β /T α and the correlation length tend to decrease. Alloys with easily activated β relaxation or more heterogeneous structure possess poor soft magnetic properties, i.e., a significant reduction in saturation magnetic flux density and an increase in coercivity. [ABSTRACT FROM AUTHOR]

• The nanoscale structural heterogeneity and magnetic properties were analyzed by atomic force microscopy and Mössbauer spectroscopy. • The nanoscale structural heterogeneity of Fe 80 Si 9 B 11 amorphous alloy attenuates monotonically with a decrease in cooling rate. • The annihilation of flow units induces the enhancement in ferromagnetic exchange interaction and weakening of magnetic anisotropy. • The ameliorated magnetic properties with decreasing cooling rate can be attributed to the degeneration of nanoscale structural heterogeneity. Despite that the nanoscale structural heterogeneity of amorphous alloys has been confirmed by advanced experimental observations and theoretical simulations, the underlying link between the structural heterogeneity and magnetic properties remains poorly known. In this work, the effect of cooling rate on the nanoscale structural heterogeneity and magnetic properties of Fe 80 Si 9 B 11 amorphous ribbons (Fe-Si-BAR) was studied by atomic force microscopy and Mössbauer spectroscopy. The results show that the degeneration of nanoscale structural heterogeneity substantially induces an improvement in soft magnetic properties with decreasing cooling rate. Specifically, the volume fraction of flow units reduces significantly with the decrease of cooling rate, and some of the flow units annihilate and transform to the ideal elastic matrix. The structural densification and reduction of the number density of quasidislocation dipole result in an enhancement in ferromagnetic exchange interaction and weakening of magnetic anisotropy. Therefore, the saturation magnetic flux density increases and coercivity decreases with reducing cooling rate. Our results provide new insight into understanding the structural mechanism in the ameliorated magnetic properties of Fe-based amorphous alloys with decreasing cooling rate. [ABSTRACT FROM AUTHOR]

• Magnetic properties of a Fe-Si-B amorphous alloy with stress gradient were studied. • Magnetic anisotropy and coercivity evolve separately. • Compressive stress hinders the reversible magnetization vector rotation. • Coercivity is irrelevant to the coherent stress. The magnetic properties and domain structure of a Fe 78 Si 9 B 13 amorphous alloy with a stress gradient from upper to the lower surface were investigated. We found that the magnetic properties of the samples vary significantly upon stress variation. Specifically, the magnetic anisotropy increases linearly with the maximum stress, whereas the coercivity, although higher than the one without stress, remains reasonably small. The phase contrast in magnetic force microscopy image and the fingerprint-like domains in magneto-optical Kerr microscopy images for ribbon surface with compressive stress demonstrate the presence of perpendicular anisotropy due to the magneto-elastic coupling. As a result, the compressive stress hinders the reversible magnetization vector rotation and makes the magnetization hard to be saturated. However, the stress causes no irreversible effects, neither on the domain wall movement nor on the magnetization rotation. Thus it is irrelevant to the coercivity. These results are different from the situation of the inhomogeneously distributed quenched-in stress enlarging the coercivity in Fe-based amorphous alloys. [ABSTRACT FROM AUTHOR]

• The nanoscale structural heterogeneity was analyzed by small-angle X-ray scattering and atomic force microscopy. • The microalloying of Co and Ni exhibits an opposite effect on the nanoscale structural heterogeneity. • The variation of mechanical behavior further proves the evolution of the nanoscale structural heterogeneity with Co and Ni substitution. • The evolution of magnetic properties induced by microalloying can be attributed to the variation of nanoscale structural heterogeneity. Nanoscale structural heterogeneity is a critical parameter for understanding the structure-property relationships in amorphous alloys. Herein, the small-angle X-ray scattering and atomic force microscopy were utilized to quantitatively investigate the nanoscale structural heterogeneity of the Fe 80- x M x Si 9 B 11 (M = Co and Ni; x = 0, 2, 4) amorphous alloys. The results show that the nanoscale structural heterogeneity of the amorphous alloys increases prominently with Ni substitution, but gradually decreases with the increase of Co content. Such evolution of structural heterogeneity was further verified by the changes in mechanical behavior. The microalloying of Ni can increase the plastic deformation ability and reduce the microhardness, whereas an opposite effect is found in the Co-doped alloys. Finally, Mössbauer spectroscopy reveals an enhancement in ferromagnetic exchange interaction and magnetic anisotropy with Co substitution, while the microalloying of Ni leads to a deteriorative result. Such variations in magnetic properties can be attributed to the evolution of nanoscale structural heterogeneity with Co and Ni additions. Our observation serves as a link between the nanoscale structural heterogeneity and magnetic properties, providing a new sight into understanding the structural origin of the changes in magnetic properties of Fe-based amorphous alloys. [ABSTRACT FROM AUTHOR]

The disastrous annealing embrittlement of Fe-based metallic glasses with excellent soft magnetic properties is a long-standing issue. In order to alleviate the annealing embrittlement without worsening the soft magnetic properties, ferromagnetic elements Co and Ni are introduced to the Fe 84 Si 2 B 13 P 1 metallic glasses. The microstructure, mechanical and magnetic properties are investigated by synchrotron diffraction, two-point bending test and magnetometry. It is found that, in contrast to Co, proper Ni substitution for Fe significantly optimizes the H c of Fe 84 Si 2 B 13 P 1 metallic glasses and keeps the B s at a high level. According to bending tests, the ductile-brittle transition temperature of the metallic glasses increases slightly with Ni substitution and decreases prominently with Co substitution. Ultimately, the ductile Fe 82 Ni 2 Si 2 B 13 P 1 metallic glasses with B s of 1.65 T and H c of 3.4 A/m have been successfully obtained. Macroscopically, the cheerful propensity to form well-distributed shear bands during bending of Ni-substituted annealed alloys contributes to their good ductility. Furthermore, the alteration of ductile-brittle transition temperature can be conducted by the structural change at the medium-range scale as revealed by the pair distribution function measurements. After annealing the compression at atomic scale ranging from 6 Å to 16 Å of Co-substituted metallic glasses may hinder the creation of well-distributed shear bands and give rise to the deterioration of bending ductility. This work provides a perspective to understand the ductile-brittle transition of metallic glasses from the atomic scale. • With proper substitution of Ni for Fe, H c of Fe 84 Si 2 B 13 P 1 alloys decreases and B s keeps at a high level. • The bending ductility of annealed ribbons improves by Ni substitution. • The Ni-substituted alloys show good propensity to form well-distributed shear bands during bending. • Medium-range structure compression of Fe 78 Co 6 Si 2 B 13 P 1 alloy results in its ductility deterioration. [ABSTRACT FROM AUTHOR]

Metallic glasses are structurally heterogeneous on the atomic and nano scales. However, few investigations have been conducted on how the structural heterogeneities in these two scales co-evolve during annealing. In this work, the atomic and nanoscale structural heterogeneity evolution accompanying the magnetic softness is systematically discussed based on the literature and our previous synchrotron X-ray diffraction and atomic force microscopy results. We revealed the co-evolution mechanism of structural heterogeneities on the atomic and nano scales during annealing via the insight of percolation theory from the point of view of the local five-fold symmetry of the clusters. The results indicate that the reduction of atomic-scale structural heterogeneity during annealing is accompanied by an increase in the degree of local five-fold symmetry of the clusters and an alteration in their connection patterns. As the local five-fold symmetry of clusters in Fe-based metallic glasses reaches the percolation threshold, the nanoscale liquid-like regions tend to transform into solid-like regions. The great degree of percolation causes the pronounced weakening of the nanoscale structural heterogeneity accompanying changes in the shape and number of the liquid-like regions. The reduction of the number of liquid-like regions causes a reduction in vertical anisotropy and magnetic softening due to a more uniform and less free volume within the sub-circular shaped liquid-like region. • The evolution of the atomic/nano scale structural heterogeneity and its relation to the magnetic softness was discussed • The co-evolution mechanism of structural heterogeneities on the atomic and nano scales during relaxation is revealed. • The shape of liquid-like regions tend to become nearly circular during relaxation contributing to magnetic softening. [ABSTRACT FROM AUTHOR]

• The relaxation-induced evolution of nanoscale structural heterogeneity is analyzed by atomic force microscopy in Fe 80 Si 9 B 11 metallic glass. • The degeneration of nanoscale structural heterogeneity induces the improvement of soft magnetic properties. • The soft magnetic properties can be optimized by selectively tailoring the intrinsic structural heterogeneity of Fe-based metallic glass. Despite the mesoscopic isotropic nature of metallic glasses, there is a certain degree of structural heterogeneity down to the nanoscale. However, how structural heterogeneity affects the magnetic properties is still unclear. In this work, the relaxation-induced structural heterogeneity and magnetic properties evolution of Fe 80 Si 9 B 11 metallic glass were investigated by atomic force microscopy (AFM) and Mössbauer spectroscopy. We revealed that the correlation-length of nanoscale heterogeneity relates closely with the ferromagnetic exchange interaction together with the magnetic anisotropy, providing experimental evidence of the intrinsic link between the nanoscale structural heterogeneity and magnetic properties for Fe-based metallic glasses. The degeneration of nanoscale structural heterogeneity induces the enhancement of the ferromagnetic exchange interaction and weakening of the magnetic anisotropy. Our results have a vital significance in understanding the structure-property relationship of metallic glass. [ABSTRACT FROM AUTHOR]

The structure-property relationships in amorphous alloys are far from being fully understood. Here we show an unusual structural rearrangement occurring over medium-range length scale prior to crystallization for a (Fe 0.5 Co 0.5) 72 Si 4 B 20 Nb 4 amorphous alloy ribbon upon heating by in-situ synchrotron diffraction, whereas the short-range structure shows no anomaly. During the above process, local stress field generates and results in the enlargement of coercivity. This can be further supported by the magnetic force microscopy images showing an enhancement of magnetic phase contrast after annealing the sample at a temperature where the unusual structural change occurs. Moreover, the average grain size derived from the transmission electron microscopy images of the crystallized (Fe 0.5 Co 0.5) 72 Si 4 B 20 Nb 4 ribbon is much smaller than that of (Fe 0.5 Co 0.5) 76 Si 4 B 16 Nb 4 , suggesting the slow crystallization kinetics caused by the local stress field. This work highlights the role of medium-range order in determining the properties of amorphous alloys. • Unusual structural change at medium-range occurs in a Fe-based amorphous alloy. • Coercivity increases drastically due to the enhanced stress-induced anisotropy. • The structural rearrangement results in slow crystallization kinetics. [ABSTRACT FROM AUTHOR]