Glass-Forming Ability and Crystallization Behavior of Mo-Added Fe_82−xSi₄B₁₂Nb₁Mo_xCu₁ (x = 0–2) Nanocrystalline Alloy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Fe-based soft magnetic alloys are perspective materials for many electrical components, such as transformers and inductors, since they have low core loss and coercivity (Hc) compared to usual silicon steel. To optimize the soft magnetic properties of the alloys a co-addition of transition metals like Mo and Nb is a promising way to reduce Hc and to increase effective permeability resulting in magnetic alloys with excellent properties for numerous applications. Therefore, the topic of the reviewed article and the results obtained are interesting and actual.

My critical comments are the following.

1. Figures should not be at the end of the article. Only inside the text !
2. The caption to Figure 2 is extremely unfortunate. It should be: Мо_х , and the scale of change of the variable Мо_х is from 0.0 to 2.0 .
3. The formatting of text between lines 161 and 174 contains defects. Expressions like ΔH_mix^AB, c_i c_j, ΔS_mix, ΔH_mix should be written with normal upper and lower indices, not in the Latex notation.
4. Can the height of nucleation barrier (Fig.4a) and the second transition barrier of amorphous+ alfa-Fe => alfa-Fe+ compound (Fig.2) be expressed through any thermodynamic parameters of the system, such as ΔHmix , ΔSmix , ΔGv , ΔG*, γ ?
5. There is a question on the mechanical strength of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ ribbons with increasing x. Mechanical properties are very important for practical applications, especially when it comes to miniaturized devices. Since the atomic mismatch (δ) increases with increasing x, one would expect the strength properties of the ribbons to deteriorate. Did the authors observe these tendencies in their experiments ?

I recommend the article for printing after the above corrections have been made.

Author Response

The full manuscript has been uploaded as a PDF file. 

Response to Reviewer 1

We sincerely thank the reviewer for the thorough reading of our manuscript and for the constructive comments and insightful suggestions. Your feedback was instrumental in helping us identify areas that required further clarification and refinement. We have carefully addressed each of your comments point by point, as detailed below.

[Comment 1]

Figures should not be at the end of the article. Only inside the text!

[Response 1]

We sincerely thank the reviewer for the helpful feedback regarding figure placement. In the original submission, figures were placed at the end of the manuscript, following common journal guidelines for initial review. However, we agree that embedding figures near their first mention improves readability and coherence.

In response, all figures have been repositioned directly after their initial citation in the text. We also reviewed and updated figure numbers, captions, and in-text references for consistency. We believe these changes enhance the clarity and overall presentation of the manuscript, and we appreciate the reviewer for pointing out this important improvement.

[Modification of the manuscript]

All figures have been appropriately repositioned within the main text, directly following their first mention, and the revised manuscript has been uploaded accordingly.

[Comment 2]

The caption to Figure 2 is extremely unfortunate. It should be: Мох, and the scale of change of the variable Мох is from 0.0 to 2.0.

[Response 2]

We appreciate the reviewer’s comment on the caption and labeling of Figure 2. In the original version, the definition and range of the compositional variable were unclear, which may have limited accurate data interpretation.

In response, we have revised the x-axis of Figure 2 to explicitly indicate “Mo contents (at.%)”, clearly denoting that the molybdenum content varies from 0.0 to 2.0 atomic percent in the Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) alloy system. This adjustment ensures a direct and intuitive correspondence between the x-axis and the compositional variable "x" used throughout the manuscript. Although the original caption “Mixing enthalpy (), mixing entropy (), and atomic mismatch () of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) melt-spun ribbons” remains scientifically accurate, we enhanced the clarity by aligning the figure labeling with the variable used in the text.

This revision enhances figure clarity and better defines the link between composition and thermodynamic properties, contributing to the overall improvement of the manuscript.

[Modification of the manuscript]

Figure 2. Mixing enthalpy (), mixing entropy (), and atomic mismatch () of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x= 0-2) melt-spun ribbons.

[Comment 3]

The formatting of text between lines 161 and 174 contains defects. Expressions like ΔH_mix^AB, c_i c_j, ΔS_mix, ΔH_mix should be written with normal upper and lower indices, not in the Latex notation.

[Response 3]

We appreciate the reviewer’s careful attention to the formatting inconsistencies in the text between lines 161 and 174. Upon review, we confirmed that several mathematical expressions such as ΔH_mix^AB, c_i c_j, and ΔS_mix were inadvertently left in LaTeX-style notation, which is not suitable for the final manuscript format. These formatting issues may hinder readability and do not align with the journal’s typesetting standards.

In the revised manuscript, these expressions have been corrected using appropriate subscript and superscript formatting to ensure clarity and consistency. We also reviewed nearby sections to confirm that no similar issues remain.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 5, lines 174-186):

“, where  is the  between A and B elements and  are atomic percent. As Mo content increases in the Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) nanocrystalline soft magnetic ribbons,  continuously decreases.

The Mo0 alloy composition exhibits a relatively small  -15.57 J·mol^-1, while the Mo2 alloy composition shows -15.99 J·mol⁻¹. This suggests that the addition of Mo enhances the negative , thereby improving GFA. For the larger negative , atomic interactions between elements strengthen, enhancing stability, suppressing crystallization, and stabilizing the supercooled liquids [17, 27, 44, 45]. These findings emphasize the role of Mo in improving GFA and achieving stable amorphous phase formation in Fe-based nanocrystalline alloys.

Higher  increases compositional disorder, hindering atomic rearrangement into a crystalline structure This disorder enhances the stability of the amorphous phase, which is advantageous for improving GFA [46, 47]. “

[Comment 4]

Can the height of nucleation barrier (Fig.4a) and the second transition barrier of amorphous+ alfa-Fe => alfa-Fe+ compound (Fig.2) be expressed through any thermodynamic parameters of the system, such as , , , ,  ?

[Response 4]

We sincerely appreciate the reviewer’s thoughtful question regarding the thermodynamic interpretation of the nucleation and phase transition behaviors observed in Figures 2 and 4a. The nucleation energy barrier illustrated in Figure 4a, as well as the secondary transition from amorphous + α-Fe to α-Fe + intermetallic compounds shown in Figure 2, can be reasonably interpreted in terms of classical thermodynamic parameters.

In the revised manuscript, we have incorporated a more detailed explanation based on classical nucleation theory. According to this framework, the critical nucleation barrier  can be expressed as follows:

        (6)

where γ represents the interfacial energy and  is the volumetric free energy change associated with the phase transformation. Furthermore,  can be approximated using the Gibbs free energy of mixing:

       (5)

These formulations highlight how the nucleation barrier is fundamentally governed by the thermodynamic stability of the system, particularly the  and configurational  of the alloy, as well as its interfacial characteristics. In the present study, these parameters were quantitatively evaluated and presented in Figure 2 to clarify the compositional influences on nucleation behavior.

In addition, the second transformation pathway, in which amorphous + α-Fe evolves into α-Fe + Fe-metalloid compounds, can also be explained through the same thermodynamic considerations, especially the changes in ​ and interfacial energy driven by solute redistribution. A supplementary discussion addressing these implications has been added to Section 3.2 of the revised manuscript.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 7-8, lines 239-244):

These thermodynamic properties emphasize the crucial role of transition metals in the crystallization process [18, 43, 52, 53]. Mo and Nb reduce  and lower , thereby increasing  and promoting nanocrystallization [51-53]. Furthermore, the second transformation process from amorphous + α-Fe to α-Fe + intermetallic compounds, as depicted in Figure 2 can also be interpreted within the same thermodynamic context. Specifically, it is influenced by variations in  and interfacial energy, indicating that both the initial nucleation and subsequent phase transitions follow a unified thermodynamic perspective.

[Comment 5]

There is a question on the mechanical strength of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ ribbons with increasing x. Mechanical properties are very important for practical applications, especially when it comes to miniaturized devices. Since the atomic mismatch (δ) increases with increasing x, one would expect the strength properties of the ribbons to deteriorate. Did the authors observe these tendencies in their experiments?

[Response 5]

We thank the reviewer for raising this important point regarding the mechanical strength of the Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) ribbons. In this study, our primary focus was on investigating the thermal and magnetic properties; thus, quantitative mechanical characterization such as tensile strength or fracture toughness was not included. However, throughout the melt-spinning process and subsequent handling of the ribbons, no noticeable signs of brittleness or mechanical degradation were observed even for samples with higher Mo content (x = 2.0), which exhibit increased atomic mismatch (). The ribbons remained intact without visible cracks, edge defects, or delamination during sample preparation and measurement.

Although this does not constitute a quantitative mechanical assessment, these observations suggest that the increased δ associated with Mo addition does not negatively affect the practical workability of the ribbons under our experimental conditions. We acknowledge that more systematic mechanical characterization is necessary to confirm these effects and plan to include such analyses in future studies.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1.) The manuscript repeatedly refers, particularly in Section 3.3, to the influence of the structural state of the analysed ribbons. Given the recurrent and logically framed argument, the manuscript lacks documentation of the microstructural evolution, at least for the two extreme states, Mo0 and Mo2.

2.) What geometry was used for the XRD measurements: Bragg-Brentano or Debye-Scherrer? This essential information is missing in the experimental section, yet it is critical for interpreting the structural evolution based on the XRD results.

3.) What was the X-ray source used in the diffractometer? If a copper anode was employed, this choice is questionable, as the absorption edge of Fe lies below the energy of Cu Kα radiation. This leads to a strong fluorescence effect in the sample, which significantly affect the obtained diffraction data. The use of a copper anode may be acceptable in this case, but the reader must have this important information about the experimental conditions.

4.) Figures 6a and 6b: On logarithmic axes, minor ticks between major values should be added to improve readability of the plotted data.

5.) Authors should reconsider the use of the term HR-TEM or HR-STEM. These terms are typically reserved for atomic-resolution imaging enabled by specific contrast mechanisms. The presented TEM images was not acquired under such conditions.

6.) Line 103: The heating rate is specified for the DSC experiment but not for the heat-treatment processing. Given that heating rate significantly influences the onset of crystallization and final crystal size, this missing information should be completed.

7.) Line 105: The sentence appears incomplete: “Before observing the microstructure of the ribbons, with high-resolution scanning transmission electron microscopy (STEM).” Please revise for grammatical correctness and clarity.

8.) Line 154: The delta symbol (Δ) appears twice. Is one redundant, or there is something missing?

9.) Line 194: What experimental evidence supports the claim that the XRD peaks result from surface crystallization rather than bulk crystallization throughout the ribbon cross-section?

10.) Line 258: According to the graph, except Mo2 all alloys exhibit comparable values of coercivity (Hc). Only the Mo2 alloy shows a significant decrease. Is the effect of Mo gradual, or does it manifest only at Mo2? This behaviour should be discussed. If the focus is on Hc at 470 °C, the recommendation is to provide an additional dedicated x–y plot for this temperature only to clearly illustrate the effect of Mo contain.

11.) Line 261: On what basis do the authors claim that nanocrystals are coarsened at 510 °C? This claim should be supported by experimental evidence.

12.) Line 310: The sentence "The EDS mapping images in Fig. 7d show the distribution of each element, while the high-angle annular dark-field (HAADF) images provide precise confirmation of the distribution of Fe, Mo, and Nb" is unclear. It should be revised or clarified. Moreover, the HAADF images do not confirm elemental distribution. The presented HAADF image depicts crystallites formed in the alloy, not the spatial distribution of elements.

Author Response

The full manuscript has been uploaded as a PDF file. 

Response to Reviewer 2

We sincerely thank the reviewer for their thorough reading of our manuscript and for the constructive comments and suggestions. We have carefully revised the manuscript based on the provided feedback. Below, we present detailed, point-by-point responses to each comment, outlining the corresponding changes made to the manuscript.

[Comment 1]

The manuscript repeatedly refers, particularly in Section 3.3, to the influence of the structural state of the analysed ribbons. Given the recurrent and logically framed argument, the manuscript lacks documentation of the microstructural evolution, at least for the two extreme states, Mo0 and Mo2.

[Response 1]

We sincerely thank the reviewer for pointing out the lack of microstructural comparison between the two compositional extents (Mo0 and Mo2), which is a critical aspect of validating the structural evolution discussed in Section 3.3. In the original manuscript, we presented detailed characterization results for the Mo2 ribbon, including STEM images, SAED patterns, grain size distributions, and EDS mappings (as shown in Fig.7), since this composition exhibited the refined nanocrystalline structure and optimal magnetic properties.

Although TEM analysis data for the Mo0 ribbon are not included, its microstructural characteristics may be reasonably inferred based on supporting evidence from XRD, DSC, and magnetic measurements. The Mo0 as-cast ribbon exhibits crystalline peaks in the XRD results, a lower onset crystallization temperature in DSC, and significantly higher coercivity (H_c) and lower permeability () compared to Mo2. In addition, as shown in Fig. 2, the mixing entropy of Mo2 is significantly higher than that of Mo0. This increase in mixing entropy results from the increased Mo content in the alloy. As discussed in Section 3.2 (Influence of Mo Addition on Nanocrystalline Structure Formation), a higher mixing entropy can reduce the nucleation energy barrier and promote the formation of more nuclei. Based on this, it can be inferred that Mo2 contains a larger number of nuclei and higher glass-forming ability facilitates the formation of a fully amorphous phase compared to Mo0. Consequently, a refined nanocrystalline matrix is formed after heat treatment.

Although we acknowledge the absence of direct microstructural data for Mo0, we believe that this set of converging indirect evidence reasonably supports the compositional influence on microstructural evolution. To better reflect the correlation between nanocrystalline refinement and magnetic performance, we have revised the main text to explicitly state that the Mo2 ribbon, characterized by its fine and uniform nanostructure, exhibits the lowest H_c and the highest maximum  among the evaluated samples. The reviewer’s comment prompted us to clarify these relationships more explicitly in the revised manuscript, thereby strengthening the logical connection between composition, structure, and magnetic properties.

Furthermore, as shown in the revised Section 3.3 (Fig. 6a–c), the magnetic measurements directly support the inference of microstructural evolution. The Mo2 ribbon exhibited the lowest H_c and the highest  under optimal annealing conditions, suggesting a highly uniform and refined nanocrystalline structure. In contrast, the Mo0 ribbon showed higher Hc and lower , consistent with insufficient amorphous stabilization and potential surface crystallization. These clear distinctions in soft magnetic properties quantitatively reflect the underlying structural differences, reinforcing the compositional effect on nanocrystalline development. The detailed analysis of these magnetic trends was incorporated to complement the lack of direct microstructural data for Mo0 and better align the experimental observations with the structural discussion.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 9-10, lines 292–309):

“As shown in Fig. 6a, the ribbons annealed at 470 °C exhibit the lowest H_c, which is attributed to optimized thermal conditions during annealing. Notably, the Mo2 ribbon exhibits an exceptionally low H_c value of 4.54 A/m, significantly lower than those of the other compositions. This indicates that the addition of Mo effectively suppresses the increase in coercivity. As further illustrated in Fig. 6b, the reduced H_c in the Mo2 composition is likely associated with decreased domain wall pinning, which allows for easier domain wall movement. This improvement in magnetic softness contributes to the improvement of superior soft magnetic properties.

The inhibition of grain growth by adding Mo leads to a more homogeneous microstructure, thereby enhancing soft magnetic properties. Conversely, at annealing temperatures above 510 °C, the H_c of the Mo0 and Mo0.5 ribbons increases markedly, likely due to nanocrystal coarsening that enhances domain wall pinning effects [1,13]. In contrast, the Mo1.5 and Mo2 ribbons maintain relatively low H_c values, indicating that an optimal Mo content plays a critical role in preserving refined microstructures and minimizing H_c. Although direct microstructural analysis was not conducted at 510 °C, the increased H_c in Mo0 and Mo0.5 strongly implies grain coarsening at this temperature. This trend is consistent with previous studies, where increased grain size is known to degrade soft magnetic performance due to enhanced pinning effects [1,6,8,12–13].”

The revised manuscript is on the Results and Discussions (page 12, lines 372-373):

“Compared to other ribbons, the Mo2 ribbon exhibits the lowest H_c and highest , reflecting the superior magnetic softness resulting from its finely refined nanocrystalline structure. Similarly, Nb is also located in the amorphous residual phase, further contributing to grain size refinement [12, 67]. These mapping results are consistent with previous studies, which indicate that the co-addition of transition metals, such as Mo and Nb, more effectively controls the refinement of the nanocrystal size compared to single-element addition [66]. The co-addition of Mo and Nb effectively suppresses grain growth, leading to the formation of fine nanocrystals.”

[Comment 2]

What geometry was used for the XRD measurements: Bragg-Brentano or Debye-Scherrer? This essential information is missing in the experimental section, yet it is critical for interpreting the structural evolution based on the XRD results.

[Response 2]

We sincerely thank the reviewer for pointing out this important omission. In our experiments, the X-ray diffraction (XRD) measurements were conducted using the Bragg-Brentano geometry with a θ–2θ configuration. The measurements were performed using Cu Kα radiation (λ = 1.5406 Å) under standard conditions, and the incident beam was aligned normal to the ribbon plane to ensure accurate detection of crystalline phases across the ribbon cross-section.

We have now revised the Experimental Section of the manuscript to include this information, which is critical for properly interpreting peak broadening, crystallite size estimation, and phase identification. We appreciate the reviewer’s attention to this detail, which has helped improve the clarity and completeness of our experimental description.

[Modification of the manuscript]

The revised manuscript is on the Experiments (page 3, lines 103-109):

“The amorphous and crystallization peaks of both as-spun and annealed ribbons were identified by X-ray diffractometry (XRD, Rigaku D/Max-2500VL/PC), using Bragg-Brentano geometry (θ–2θ configuration) with Cu Kα radiation ( = 1.5406 Å). The incident beam was aligned perpendicular to the ribbon surface, and measurements were conducted from the free side. Microstructural observations were performed using high-magnification scanning transmission electron microscopy (STEM), with cross-sectional samples prepared accordingly. The H_c, relative permeability () was measured using a DC B-H loop tracer (REMAGRAPH C-500) under an applied field of 800 A/m, while the M_s was determined by a vibrating sample magnetometer (VSM, Riken Denshi, BHV-525) with an applied field up to 15,000 O_e.”

[Comment 3]

What was the X-ray source used in the diffractometer? If a copper anode was employed, this choice is questionable, as the absorption edge of Fe lies below the energy of Cu Kα radiation. This leads to a strong fluorescence effect in the sample, which significantly affect the obtained diffraction data. The use of a copper anode may be acceptable in this case, but the reader must have this important information about the experimental conditions.

[Response 3]

We thank the reviewer for this insightful comment regarding the X-ray source. The XRD measurements in our study were carried out using a Rigaku D/Max-2500VL/PC diffractometer equipped with a Cu Kα radiation source (λ = 1.5406 Å), operating under a Bragg–Brentano geometry. This information has now been explicitly added to the revised manuscript.

We fully acknowledge the reviewer’s concern regarding the potential fluorescence effects when using Cu Kα radiation for Fe-based alloys, as the absorption edge of Fe (~7.11 keV) lies just below the energy of Cu Kα (~8.04 keV). Indeed, this can lead to an increase in background intensity due to Fe fluorescence. However, in our experimental setup, this effect did not hinder the identification of key diffraction peaks. The amorphous halo and crystalline peaks were well-resolved, allowing reliable phase analysis and structural interpretation.

We have now included this clarification in the Experimental Section, and we will consider using radiation sources less susceptible to fluorescence for future studies involving Fe-rich materials to further improve data quality.

[Modification of the manuscript]

The revised manuscript is on the Experiments (page 3, lines 103-109):

“The amorphous and crystallization peaks of both as-spun and annealed ribbons were identified by X-ray diffractometry (XRD, Rigaku D/Max-2500VL/PC), using Bragg–Brentano geometry (θ–2θ configuration) with Cu Kα radiation ( = 1.5406 Å). The incident beam was aligned perpendicular to the ribbon surface, and measurements were conducted from the free side. Microstructural observations were performed using high-magnification scanning transmission electron microscopy (STEM), with cross-sectional samples prepared accordingly. The H_c, relative permeability () was measured using a DC B-H loop tracer (REMAGRAPH C-500) under an applied field of 800 A/m, while the M_s was determined by a vibrating sample magnetometer (VSM, Riken Denshi, BHV-525) with an applied field up to 15,000 O_e.”

[Comment 4]

 Figures 6a and 6b: On logarithmic axes, minor ticks between major values should be added to improve readability of the plotted data.

[Response 4]

We thank the reviewer for the valuable and detailed comment. We fully agree that the lack of minor ticks on the logarithmic axes may hinder precise interpretation of the impedance behavior, especially across wide frequency ranges. As suggested, we have revised Figures 6a and 6b to include minor ticks between the major values on the logarithmic frequency axis to enhance clarity and readability.

We appreciate the reviewer’s thoughtful suggestion, which helped improve the presentation quality of our data.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 9-10, lines 292–299):

“As shown in Fig. 6a, the ribbons annealed at 470 °C exhibit the lowest H_c, which is attributed to optimized thermal conditions during annealing. Notably, the Mo2 ribbon exhibits an exceptionally low H_c value of 4.54 A/m, significantly lower than those of the other compositions. This indicates that the addition of Mo effectively suppresses the increase in coercivity. As further illustrated in Fig. 6b, the reduced H_c in the Mo2 composition is likely associated with decreased domain wall pinning, which allows for easier domain wall movement. This improvement in magnetic softness contributes to the improvement of superior soft magnetic properties”

Figure 6. (a) Variation in H_c of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) ribbons as a function of annealing temperature, (b) Variation in H_c with Mo content for Fe₈₂₋ₓSi₄B₁₂Nb₁MoₓCu₁ (x=0–2) ribbons annealed at 470 °C for 10 minutes, (c) Variation in  of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) ribbons, (d) Variation in M_s of Mo1.5, Mo2 ribbons annealed at 430-510 °C for 10 min.

[Comment 5]

 Authors should reconsider the use of the term HR-TEM or HR-STEM. These terms are typically reserved for atomic-resolution imaging enabled by specific contrast mechanisms. The presented TEM images was not acquired under such conditions.

[Response 5]

We sincerely thank the reviewer for the insightful comment regarding the use of the term “high-resolution STEM.” We understand that the term “high-resolution STEM” may imply a level of resolution and instrumentation that goes beyond the conditions used in our study. In this manuscript, the term was intended to refer to high-magnification STEM images capable of identifying the size and distribution of nanocrystals.

To avoid overstatement and prevent possible confusion for readers, we have replaced “high-resolution STEM” with “high-magnification scanning transmission electron microscopy (STEM)” in the revised manuscript. This change has been implemented in the Experimental section and relevant figure captions.

We appreciate the reviewer’s suggestion, which has helped us improve the clarity and precision of terminology in our manuscript.

[Modification of the manuscript]

The revised manuscript is on the Experiments (page 3, lines 108-109):

“Microstructural observations were performed using high-magnification scanning transmission electron microscopy (STEM), with cross-sectional samples prepared accordingly. “

[Comment 6]

 Line 103: The heating rate is specified for the DSC experiment but not for the heat-treatment processing. Given that heating rate significantly influences the onset of crystallization and final crystal size, this missing information should be completed.

[Response 6]

We sincerely thank the reviewer for this valuable comment. We fully agree that the heating rate during annealing plays a crucial role in determining the crystallization behavior and final nanostructure of the material. In our study, the isothermal annealing process was conducted after placing the ribbons in a preheated muffle furnace that had already reached the target temperature. Therefore, the heating was effectively instantaneous with no ramping stage, corresponding to a rapid heating condition. This point has now been clarified in the revised Experiments section.

[Modification of the manuscript]

The revised manuscript is on the Experiments (page 3, lines 101):

“The ribbons were isothermally annealed in a muffle furnace at temperatures ranging from 430 to 550 °C for 10 minutes in an argon atmosphere, with rapid heating achieved by placing the samples directly into a muffle furnace.”

[Comment 7]

 Line 105: The sentence appears incomplete: “Before observing the microstructure of the ribbons, with high-resolution scanning transmission electron microscopy (STEM).” Please revise for grammatical correctness and clarity.

[Response 7]

We thank the reviewer for pointing out the grammatical issue in the sentence. It was confirmed that the sentence had been inadvertently left incomplete due to an oversight during manuscript preparation. We have now revised the sentence to ensure clarity and grammatical correctness.

[Modification of the manuscript]

The revised manuscript is on the Experiments (page 3, lines 108-109):

“Microstructural observations were performed using high-magnification scanning transmission electron microscopy (STEM), with cross-sectional samples prepared accordingly.”

[Comment 8]

 Line 154: The delta symbol () appears twice. Is one redundant, or there is something missing?

[Response 8]

We sincerely thank the reviewer for pointing out the duplication of the delta symbol in Line 154. Upon careful review, we found that the delta symbol () was unintentionally repeated due to a typographical error. This has now been corrected in the revised manuscript to reflect the appropriate notation.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 5, lines 167-168):

“Fig. 2 presents the calculation of , , and  value for _Fe82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) nanocrystalline alloy composition.”

[Comment 9]

 Line 194: What experimental evidence supports the claim that the XRD peaks result from surface crystallization rather than bulk crystallization throughout the ribbon cross-section?

[Response 9]

Thank you for your insightful comment regarding the origin of the XRD peaks and the experimental evidence supporting the interpretation that they result from surface crystallization rather than bulk crystallization throughout the ribbon cross-section.

The XRD patterns presented in Fig. 2 were obtained from the free side of the melt-spun ribbons, which is the surface exposed to ambient air during rapid solidification. In samples with lower Mo content, localized crystallization was observed on the free side due to the reduced glass-forming ability (GFA), as also discussed in the main text in relation to the deterioration of magnetic properties.

We conducted additional XRD measurements on the wheel side of the ribbons, which was in direct contact with the copper wheel during melt spinning. The results of this additional analysis are provided in the response to the reviewer. In all compositions, XRD results of the wheel side ribbons exhibited broad pattern, indicating the formation of a fully amorphous phase. This strongly supports that crystallization occurred selectively on the free side where the cooling rate was relatively lower.

These results are consistent with the thermal gradient conditions inherent to the melt-spinning process. The wheel side, being in direct contact with the high-thermal-conductivity Cu wheel, experiences rapid cooling that favors amorphous structure formation. The free side, being cooled by air, experiences a reduced cooling rate that facilitates crystallization in compositions with limited glass-forming ability [Refer.].

Therefore, the comparative XRD analysis of the free side and wheel side confirms that the observed diffraction peaks originate from surface crystallization rather than bulk crystallization, which substantiates the interpretation presented in this study.

[Refer.] Gao, J.; Wei, Y.; Zhao, H.; Qin, F.; Zhang, T. Anomalous Precipitation of the γ-Fe Phase in Fe-Based Nanocrystalline Alloys and Its Impact on Soft Magnetic Properties. Acta Mater. 2023, 246, 118682.

According to Gao et al. [Refer.], the high thermal conductivity of the copper roller enables the wheel-side surface of melt-spun ribbons to undergo ultra-rapid quenching with a cooling rate exceeding 10⁹ K/s, which effectively suppresses crystallization and stabilizes a fully amorphous structure. In contrast, the free side, being cooled by air, exhibits a relatively lower cooling rate though still above 10⁶ K/s which may intersect the α-Fe phase formation region in compositions with limited glass-forming ability. As a result, partial crystallization can occur near the surface, while the rest of the material solidifies into an amorphous matrix.

Response Fig 3. XRD patterns of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x= 0-2) melt-spun ribbons illustrating the effect of varying Mo content: (a) Free side (b) Wheel side.

[Comment 10]

  Line 258: According to the graph, except Mo2 all alloys exhibit comparable values of coercivity (H_c). Only the Mo2 alloy shows a significant decrease. Is the effect of Mo gradual, or does it manifest only at Mo2? This behaviour should be discussed. If the focus is on H_c at 470 °C, the recommendation is to provide an additional dedicated x–y plot for this temperature only to clearly illustrate the effect of Mo contain.

[Response 10]

We thank the reviewer for this valuable observation. We acknowledge that our original description may have given the impression that the effect of Mo appears only at the Mo2 composition. However, our intention was to emphasize that the Mo2 alloy exhibits the most significant reduction in H_c among all compositions.

As shown in Fig. 6a, the lowest H_c is observed for the Mo2 ribbon annealed at 470 °C, indicating that this condition achieves the most favorable soft magnetic properties.

To clarify this effect and strengthen our discussion, we have revised the corresponding paragraph in the manuscript and additionally included a dedicated x–y plot (Fig. 6b) highlighting the H_c values of all samples annealed at 470 °C.

Furthermore, the sharp drop in H_c observed for Mo2 suggests that Mo addition plays a critical role in reducing domain wall pinning and enhancing magnetic softness. Although direct structural analysis was not conducted, the observed magnetic behavior may be associated with Mo-induced effects such as improved thermal stability, enhanced nucleation tendency, or facilitated Cu clustering, which have been reported to contribute to the development of refined magnetic microstructures and reduced coercivity in similar systems.

Compared to the other compositions, the Mo2 alloy exhibits the highest mixing entropy and atomic mismatch, which not only enhances its glass-forming ability (GFA) but also promotes the formation of a greater number of nuclei during the nanocrystallization stage, as confirmed by thermodynamic calculations. Accordingly, as shown in Figure 6(b), the coercivity of Mo0, Mo0.5, and Mo1 which contain pre-existing crystalline phases is relatively high, whereas Mo1.5 and Mo2 exhibit significantly lower coercivity. Notably, the Mo2 alloy shows the lowest coercivity compared to other compositions, and it also demonstrates the highest permeability. We confirmed that the Mo2 alloy possesses the most favorable characteristics through magnetic properties, the presence of a fully amorphous structure in the as-spun ribbon, and the thermodynamic analysis. Furthermore, the nanocrystal size observed in Figure 7 for the Mo2 alloy is remarkably fine, averaging below 20 nm. Such refinement is believed to enhance the magnetic properties through stronger exchange interactions between the nanocrystals.

We have incorporated this explanation in the revised manuscript to more clearly clarify why the Mo2 composition exhibits distinctly superior magnetic properties compared to the other samples.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 9, lines 292–299):

“As shown in Fig. 6a, the ribbons annealed at 470 °C exhibit the lowest H_c, which is attributed to optimized thermal conditions during annealing. Notably, the Mo2 ribbon exhibits an exceptionally low H_c value of 4.54 A/m, significantly lower than those of the other compositions. This indicates that the addition of Mo effectively suppresses the increase in coercivity. As further illustrated in Fig. 6b, the reduced H_c in the Mo2 composition is likely associated with decreased domain wall pinning, which allows for easier domain wall movement. This improvement in magnetic softness contributes to the improvement of superior soft magnetic properties.”

Figure 6. (a) Variation in H_c of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) ribbons as a function of annealing temperature, (b) Variation in H_c with Mo content for Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) ribbons annealed at 470 °C for 10 minutes, (c) Variation in  of Fe_82-xSi₄B₁₂Nb₁Mo_xCu₁ (x=0-2) ribbons, (d) Variation in M_s of Mo1.5, Mo2 ribbons annealed at 430-510 °C for 10 min.

[Comment 11]

  Line 261: On what basis do the authors claim that nanocrystals are coarsened at 510 °C? This claim should be supported by experimental evidence.

[Response 11]

We thank the reviewer for raising this important point. Although we did not directly obtain XRD or TEM data for the samples annealed at 510 °C, our interpretation is based on the magnetic behavior—particularly the significant increase in H_c observed for the Mo0 and Mo0.5 ribbons under this condition. In soft magnetic materials, such a sharp rise in H_c is commonly associated with nanocrystal coarsening, as larger grains enhance domain wall pinning and impede magnetic reversibility.

At elevated annealing temperatures, increased atomic mobility promotes grain boundary migration and grain growth. This thermal effect likely leads to the coarsening of nanocrystals in Mo0 and Mo0.5 ribbons at 510 °C, which in turn causes a degradation in soft magnetic performance. This interpretation is supported by previous studies: Herzer [1,13] provided a theoretical framework showing how increased grain size elevates H_c through enhanced domain wall pinning; Matsuura et al. [6] reported magnetic property degradation resulting from microstructural evolution under high-temperature annealing; Yoshizawa et al. [8] highlighted the importance of ultrafine grain structures in maintaining low Hc; and Lashgari et al. [12] reviewed how thermal and compositional factors influence grain growth and coercivity in Fe-based alloys.

In contrast, the Mo1.5 and Mo2 ribbons maintain relatively low H_c values even at 510 °C. This implies that an optimal Mo content helps suppress nanocrystal coarsening by enhancing thermal stability and inhibiting grain boundary motion, possibly due to solute drag or reduced atomic diffusivity. We have clarified this interpretation in the revised manuscript and added the relevant references to support this explanation.

[Modification of the manuscript]           

The revised manuscript is on the Results and Discussions (page 9-10, lines 300-306):

“In contrast, the Mo1.5 and Mo2 ribbons maintain relatively low H_c values, indicating that an optimal Mo content plays a critical role in preserving refined microstructures and minimizing H_c. Although direct microstructural analysis was not conducted at 510 °C, the increased H_c in Mo0 and Mo0.5 strongly implies grain coarsening at this temperature. This trend is consistent with previous studies, where increased grain size is known to degrade soft magnetic performance due to enhanced pinning effects [1,6,8,12–13]”

[Mentioned Refer]

[1] Herzer, G. Nanocrystalline soft magnetic alloys. Handb. Magn. Mater. 1997, 10, 415–462.

▪ Presents a theoretical model showing how nanocrystal coarsening increases domain wall pinning and H_c.

[6] Matsuura, M.; Nishijima, M.; Takenaka, K.; Takeuchi, A.; Ofuchi, H.; Makino, A. Evolution of fcc Cu clusters and their structure changes in the soft magnetic Fe_85.2Si₁B₉P₄Cu_0.8 (NANOMET) and FINEMET alloys observed by X-ray absorption fine structure. J. Appl. Phys. 2015, 117, 17D124.

▪ Reports degradation in magnetic properties due to grain growth and Cu cluster evolution at elevated annealing temperatures.

[8] Yoshizawa, Y.; Oguma, S.; Yamauchi, K. New Fe-based soft magnetic alloys composed of ultrafine grain structure. J. Appl. Phys. 1988, 64, 6044–6046.

▪ Demonstrates that loss of ultrafine grain structure through coarsening leads to increased H_c and reduced soft magnetic behavior.

[12] Lashgari, H.; Chu, D.; Xie, S.; Sun, H.; Ferry, M.; Li, S. Composition dependence of the microstructure and soft magnetic properties of Fe-based amorphous/nanocrystalline alloys: A review study. J. Non-Cryst. Solids 2014, 391, 61–82.

▪ Reviews how alloy composition and annealing temperature affect grain coarsening and magnetic deterioration in Fe-based nanocrystalline alloys.

[13] Herzer, G. Nanocrystalline soft magnetic materials. J. Magn. Magn. Mater. 1992, 112, 258–262.

▪ Provides a direct relationship between grain coarsening, enhanced domain wall pinning, and H_c increase.

[Comment 12]

 Line 310: The sentence "The EDS mapping images in Fig. 7d show the distribution of each element, while the high-angle annular dark-field (HAADF) images provide precise confirmation of the distribution of Fe, Mo, and Nb" is unclear. It should be revised or clarified. Moreover, the HAADF images do not confirm elemental distribution. The presented HAADF image depicts crystallites formed in the alloy, not the spatial distribution of elements.

[Response 12]

We appreciate the reviewer’s insightful and technically accurate comment regarding the interpretation of HAADF images. We fully acknowledge that HAADF (High-Angle Annular Dark Field) imaging, used in STEM, provides contrast based on the atomic number, where heavier elements appear brighter due to increased electron scattering at high angles. However, HAADF imaging does not provide direct elemental distribution; instead, it highlights structural morphology and crystallite boundaries with atomic-number-sensitive contrast.

Our original intent was to distinguish between the structural information obtained from the HAADF images and the elemental distribution revealed by EDS mapping. However, we agree that the original sentence was unclear and may have caused confusion. Therefore, we have revised the sentence for clarity as follows:

We thank the reviewer again for pointing out this important clarification.

[Modification of the manuscript]

The revised manuscript is on the Results and Discussions (page 12, lines 367-369):

“The EDS mapping images in Fig. 7d show the spatial distribution of each element (Fe, Mo, and Nb), while the corresponding high-angle annular dark-field (HAADF) image highlights the nanocrystalline morphology and contrast due to atomic number differences.”

Author Response File: Author Response.pdf