Fabrication and Properties of Axially Compressed Isotropic Epoxy-Bonded NdFeB Magnets with Partial Rare-Earth Substitution

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors studied the effect of LaCe substitution on the magnetic properties of the bonded magnets. The experiments are properly designed. The structure of the manuscript is logically organized. Some improvements can be considered to improve the manuscript quality.

1. In the introduction, please clearly state the innovation of this work. What have been done in compression molding for NdFeB and how does the results achieved in this work compared to the literature?
2. The dash sign in equation 1 is confusing and can be mistaken as the minus sign.
3. Page 3, how much difference is there by magnetizing the samples while they are hot compared to cooled to RT?
4. Use a higher image quality for figure 4.
5. In figure 5, the x=0 data has an obvious endothermal event at ~520. What is this event if it is not the Curie temperature?
6. Page 12, please elaborate on the underlying reasons for the improved beta after substitution. 
7. The author stressed that less epoxy ratio could improve magnetic properties at the cost of the mechanical properties. How does the two epoxy ratios compare in terms of the mechanical properties?

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

This work investigates the fabrication and performance of axially compressed isotropic epoxy-bonded Nd-Fe-B magnets derived from melt-spun powders. The study only emphasizes that the as-prepared magnets outperform existing commercial products in terms of temperature stability. It is recommended that the performance gaps between the prepared magnets and commercial products in other aspects can also be clarified. In addition, the data require in-depth interpretation rather than merely describing the content presented in the figures. The paper contains numerous formatting issues, and its overall quality is deemed insufficient to meet the requirements for scientific paper publication.

1. Although the refined data in the figures are in excellent agreement with the experimental data, it is advisable to provide parameters that reflect the quality of the Rietveld refinement, such as the R factors.
2. For the two groups (x=5 and x=8) with relatively small Curie temperature variations, would the M-T measurement be more accurate?
3. The enhanced temperature stability after substitution should be elaborated with detailed explanations.
4. The units of magnetic parameters in the paper need to be unified. For instance, the unit of coercivity (H_c) is inconsistently expressed as kA/m in some cases and T in others.
5. According to Equation (1), the substitution ratios on the horizontal axis of Figure 7 were calculated as 20%, 30% and ~80% . Is this calculation correct?
6. The paper states that “Additionally, increasing the powder fraction from 95-5% to 96.5-3.5% enhances the magnetic parameters in all compositions, as evident from the broader and higher loops.” However, this trend is not observed in Table 4.
7. Why is the unit of density expressed as gr/cm²?
8. Unify the chemical formula format of the initial powder materials.
9. Why is the REFe₂ phase not detected when LaCe substitution is performed at x=21?
10. Figures 4 and 9 cannot directly adopt the original test graphs from the equipment, they should be replaced with standardized graphs.

 

 

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

General Comments:

This paper describes the fabrication, characterization, and performance of axially compressed, epoxy-bonded isotropic Nd-Fe-B permanent magnets produced from melt-spun powders. The study focuses on the partial substitution of Neodymium-Praseodymium (Nd-Pr) with more abundant and cost-effective light rare-earth elements, Lanthanum (La) and Cerium (Ce). Four alloy compositions and two powder-to-binder weight ratios (95:5 and 96.5:3.5) were investigated.
The work establishes that the resulting magnets can reach densities up to 80% of the theoretical value through high-pressure axial compaction (~500 MPa). Furthermore, the study demonstrates that substituting up to 80% of the RE content with La-Ce is possible while maintaining the tetragonal 2:14:1 phase at high weight fractions (~95 wt.%), which is a significant level of substitution for maintaining hard-magnetic properties. A notable finding is that the temperature coefficients for coercivity and maximum energy product are reported to be superior (lower in magnitude) compared to commercial pure or bonded Nd-Fe-B magnets.

Despite the interesting nature of the study, there are several conceptual and technical issues that the authors must address:

• The authors refer to the compositions as "high-entropy Nd-Fe-B-type alloys". Traditionally, high-entropy alloys require five or more elements in near-equiatomic proportions. In this case, the structure remains dominated by the 2:14:1 tetragonal phase. Labeling this system as "high-entropy" appears exaggerated or technically inaccurate;
• The manuscript lacks a detailed microstructural investigation. The inclusion of SEM (Scanning Electron Microscopy) images and EDS (Energy Dispersive Spectroscopy) mapping is essential to confirm phase distribution homogeneity and the quality of the powder/binder interface;
• The reduction in lattice parameters is attributed to Ce^{3+}/Ce^{4+} ionic substitution. However, this claim is not supported by experimental data, such as XPS (X-ray Photoelectron Spectroscopy) or XANES (X-ray Absorption Near Edge Structure). Without such data, the explanation remains speculative;
• Figure 9 is of very low quality, and its description in the text is insufficient. Furthermore, the authors claim the curves exhibit a "sharp knee". Visually, the second quadrant of isotropic bonded magnets is typically much more linear; a true "sharp knee" is generally only prominent in high-quality sintered magnets;
• While the 95:5 ratio was chosen to ensure mechanical properties, no compression or tensile strength tests were provided to validate this. Additionally, Nd-Fe-B magnets containing La-Ce are highly sensitive to corrosion. The study would benefit significantly from accelerated aging tests or chemical stability analysis for industrial context;
• The general formula presented for the alloys is confusing and unconventional, which hinders the reproducibility of the study;
• Finally, the text requires a thorough grammatical review. There are also errors in mathematical notations and units. In addition, several figures feature fonts that are too small to be legible.

 

Conclusion: While the development of a scalable methodology for high-density isotropic magnets with low-cost substitutions is of interest, the points mentioned above regarding conceptual rigor and characterization must be addressed before the paper can be reconsidered for publication.

 

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

The authors of manuscript “Fabrication and properties of axially compressed isotropic epoxy-bonded Nd–Fe–B magnets with partial rare-earth substitution” describe results of rare-earth substitution in Nd-Fe-B type permanent magnets and their influence on magnetic properties. While the work shows interesting results, some corrections are required, especially concerning magnetic properties:

In the sentence in lines 244-245 authors write that Ms and Mr gradually decrease with increasing substitution, but from Fig. 6, it is visible that this is not true. The sample with x=8 has the lowest Ms, and the sample with x=5 has the largest. Furthermore, the M(H) curves do not seem to be fully saturated.

A little lower in the text, in the sentence in lines 250-251, you mention the dilution of the magnetic Fe sublattice. It should be corrected.

The scales of the bottom and middle/top x-axes on Figure 6 are different.

The label for the x-axis in Figure 7 is x, but the values do not agree with that. What are they?

Sentence in lines 312-314 states that the “increase of powder fraction … enhances the magnetic parameters in all composites”. According to the results presented in Table 4, it is not true and should be correct. The statement is repeated in lines 344-346.

The section concerning the temperature dependence of magnetic properties must be rewritten. The way the experiment was performed and the parameters (what is T0, Hcj, Hcb, what do the alpha and betta parameters mean) must be better explained. Why does Figure 10 show the median values and not the values for each sample? Furthermore, the sentence in lines 361-362 is confusing, and the reference [13] is about something else.

 

Some other issues:

In conclusion, you wrote that the substitution is up to 80%, whereas in the main part of the text, it is 21%.

No information in the Materials and Methods section about measurements of particle sizes and their distribution.

The quality of Figures 4, 8 and 9 is very low and must be improved. The axis and the values must be well visible.

When introducing the full composition of your alloy, please explain what you mean by writing different elements in brackets, like (Nd-Pr), (La-Ce) or (Co, Zr). Typically, it refers to the substitution of one element for another, so what are the substitution levels?

Table 2, it should be g, not gr, for grams.

Caption of Tables 1 and 2 uses the RE-HEAx abbreviation not introduced in the text.

Line 155, the sentence should be corrected.

Author Response

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Before the article is accepted for publication, the following minor issues need to be revised:

1.Table 4 has been modified, but the table caption has not been updated.

2.There are two sections labeled 3.3 in the article.

3.Regarding the use of symbols such as B_r, some appear to have been created using the formula editor, while others were typed directly. Please standardize this.

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

The authors have satisfactorily addressed most of the concerns raised in the previous review round.

Regarding the suggestion for mechanical and corrosion testing, the authors acknowledged this limitation. While direct corrosion tests would strengthen the industrial relevance of La-Ce substituted magnets, their expanded analysis of thermal stability (temperature coefficients) provides a reasonable alternative metric for stability within the scope of this specific study. The explanation regarding the Ce3+/Ce4+ ionic substitution is now properly framed as a hypothesis supported by literature rather than a direct experimental finding, which is acceptable.

The manuscript is now technically sound and suitable for publication.

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

I appreciate the corrections made by the authors; they have significantly improved the manuscript. However, I still have minor issues.
-    Again, the problem with up to 80% substitutionn mentioned in conclusion. It should be 75% (as in revised Figure 8).
-    Another two issues concern the description of magnetic properties. In the sentence starting in line 430, you write about “... improved β coefficient observed after (La,Ce) substitution …”. But in the text, you mention only one value of the β coefficient, probably the mean one. Therefore, it is impossible to verify this statement. It could be possible if not the second issue that concerns the description of Figure 11 (paragraph starting from line 437). In the text, you write that this figure shows Hcj data, while it presents Hcb.
-    Again, the ticks of Figure 7 (in revised version) are different for the top/middle and bottom x axis, as well as for the left and right of the y axis. It must be corrected.

Author Response

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