The Structure and Magnetic Properties of Sm₂Fe₁₇C_x Compounds Prepared from Ball-Milled Mixtures of Sm₂Fe₁₇ and Carbon Nanotubes or Graphite

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please see the attached file. 

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

 

We are very grateful for your contribution to improving the quality of our article. We have thoroughly read your suggestions.

Q1: The reviewer suggests adding remarks on the potential application of Sm2Fe17 carbides as permanent magnets based on post-study findings. (How is coercivity/magnetization evaluated in comparison -for ex.- to Sm2Fe17 nitrides? Is it feasible to build a PM based on the investigated compounds?

A1:We have added remarks on potential applications of Sm2Fe17 carbides in the end of Results and Discussions section.

We have significantly improved the content of our paper with the help of your comments and suggestions and highly appreciate for that.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors obtained Sm2Fe17Cx, hard magnetic material, by ball milling method. The manuscript is written relatively well but some improvements to manuscript should be made.

Line 124 " The cell volume of Sm2Fe17Cx in CNT and graphite mixtures was 0.7906 ± 0.0004 and 125 0.7914 ± 0.0007 nm3, respectively, which corresponds to x = 0.2 ± 0.1 and 0.3 ± 0.1."

It is not clear how x is obtained.  Method description or references should be given.

The fitting to Mossbauer spectra is not perfect. Since the presence of carbon  may lead to iron carbide phases (θ -Fe3C and χ -Fe5C2) it is necessary to check whether subspectra of the iron carbides can prove fitting.  More information about carbides see: DOI: 10.1038/srep26184

Line 215 "The decrease of Sm2Fe17Cx mass fraction caused by these two phases formation  implies excessive carbon presence in the mixtures that can not be observed with XRD."  Carbon can be in pure crystalline iron carbides.

Line 232 "After annealing, hyperfine field parameter values µ0H of Fe atoms located in each of the Sm2Fe17Cx lattice sites increased, which indicates growth of atomic magnetic moments induced by interstitial carbon presence."

The relationship between hyperfine field and atomic valence state is complex - consist of several contribution. So it is not possible make such conclusion so easily. The change in hyperfine field is rather the consequence of annealing. At different sites, hyperfine field is different, so it depends on the distance to neigbouring iron and rare earth atoms. The annealing leads to more sharp Mossbauer lines, smaller linewidth, i.e. it may means better crystalline structure

What size of jar and balls used for milling?

Line134 "The first sextet in the Table 2 has an isomer shift value Is of 0.07 mm/s and a hyperfine magnetic field value µ0Hhf of 32.9 T, which corresponds to the α-Fe phase." Is isomer shift given relatively to α-Fe or source? Then what the matrix of 57Fe source? If is given relatively  to α-Fe the discrepancy may be too large. Indicate errors of parameters.

Tables captions

List and indicate names of given parameters

Comments on the Quality of English Language

Line 132-133, "specter" should be spectrum or spectra

Figure 3 "caculated" -calculated

              "velosity" -velocity

Author Response

Dear Reviewer,

We are very grateful for your contribution to improving the quality of the manuscript. We have thoroughly read all of your comments and suggestions.

The answers are listed in the same order as the comments and suggestions were:
Q1: Line 124 " The cell volume of Sm2Fe17Cx in CNT and graphite mixtures was 0.7906 ± 0.0004 and 125 0.7914 ± 0.0007 nm3, respectively, which corresponds to x = 0.2 ± 0.1 and 0.3 ± 0.1."
It is not clear how x is obtained.  Method description or references should be given.
A1: Thank you for the comment, the values of x were calculated by cell volume measurements using formula (2), which is described in Section 2.2 and additionally indicated a link to the calculation methodology in the text of the paper.

Q2: The fitting to Mossbauer spectra is not perfect. Since the presence of carbon  may lead to iron carbide phases (θ -Fe3C and χ -Fe5C2) it is necessary to check whether subspectra of the iron carbides can prove fitting.  More information about carbides see: DOI: 10.1038/srep26184
A2: Thank you for this valuable point. According to [DOI: 10.12989/amr.2017.6.3.245, and DOI: 10.1016/j.apt.2021.06.024], the formation of cementite after high-energy ball milling is possible for a similar system. We tried fitting cementite spectrum, but this did not lead to a better description of the Mössbauer spectrum. However, we have added corresponding references (including recommended one) in the Results and Discussion section.

Q3: Line 215 "The decrease of Sm2Fe17Cx mass fraction caused by these two phases formation  implies excessive carbon presence in the mixtures that can not be observed with XRD."  Carbon can be in pure crystalline iron carbides.
A3: We very appreciate you for the comment about line 215. We have changed the discussion of Mössbauer spectroscopy results.

Q4: The relationship between hyperfine field and atomic valence state is complex - consist of several contribution. So it is not possible make such conclusion so easily. The change in hyperfine field is rather the consequence of annealing. At different sites, hyperfine field is different, so it depends on the distance to neigbouring iron and rare earth atoms. The annealing leads to more sharp Mossbauer lines, smaller linewidth, i.e. it may means better crystalline structure
A4: Thank you for the significant remark about line 232, this is true so we have used softer wording in both the discussion of Mössbauer study of annealed samples and Conclusions.

Q5: What size of jar and balls used for milling?
A5: Thank you for noting the absence of jar volume and the size of balls, we have extended the 2.1 Materials subsection.

Q6: Line134 "The first sextet in the Table 2 has an isomer shift value Is of 0.07 mm/s and a hyperfine magnetic field value µ0Hhf of 32.9 T, which corresponds to the α-Fe phase." Is isomer shift given relatively to α-Fe or source? Then what the matrix of 57Fe source? If is given relatively  to α-Fe the discrepancy may be too large. Indicate errors of parameters.
A6: Thank you for finding a misprint about isomer shift of the a-Fe phase, the calibration of spectra was made relatively to α-Fe. Also, we have indicated errors of Mössbauer spectra parameters.

Q7: Tables captions
List and indicate names of given parameters
A7: The parameters are now indicated in the footers of all the Tables, we appreciate your guidance.

Q8: Line 132-133, "specter" should be spectrum or spectra
Figure 3 "caculated" -calculated
              "velosity" -velocity
A8: Thanks for your attentiveness, we have corrected the spelling in the Figure 3, and made minor language corrections in the whole manuscript.

We have substantially improved the content of our paper with the help of your comments and suggestions and highly appreciate for that.

Reviewer 3 Report

Comments and Suggestions for Authors

In the manuscript ' The structure and magnetic properties of Sm2Fe17Cx compounds prepared from ball-milled mixtures of Sm2Fe17 and carbon nanotubes and graphite' authors synthesized and gave thorough analysis of structure and magnetic properties of targeted compounds. Introduction was given briefly containing the most interesting open topics regarding Sm2Fe17C and related magnetic materials. The influence of carbon modification on the structure and magnetic properties was posed as a central question and motivation for this research. Materials and methods used in this study are sufficiently described.  Results are presented in clear and analytical form with strong conclusions derived. The real joy for the reader was to have clearly presented experimental data and relevant conclusions that steam from them without unfounded scenarios we frequently meet with in papers. For entire work on this interesting subject I would like to thank the authors and to recommend this paper for publication in Metals, however after clarification of minor remarks:

1. In the 2.1 chapter it would be useful to give temperature range for annealing as stated later in the manuscript (I think only at p6)

2. Page 3, line 132 and 133: Möss specter should be changed to Möss spectrum

3. line 146 I didnt understand how relative areas of the sextets corresponds well to site occupancies, especially it is not the case for M+A samples. Please, explain. Also there are strong disagreement about percentage of alpha iron from XRD and Mossbauer fit for M+A CNT samples. Discuss.

4. Did you collect Moss room T spectrum for graphite M and M+A samples? Are they similar to CNT?

5. I was wondering if is it possible to find C in lattice sites, not only in interstitial sites?

There is a record of monoclinic C2/m structure, please see:

https://next-gen.materialsproject.org/materials/mp-1219267#crystal_structure

in comparison to

https://next-gen.materialsproject.org/materials/mp-1426/#crystal_structure

you have obtained. I would appreciate to hear your opinion.

Author Response

Dear Reviewer,

We are very grateful for your contribution to improving the quality of the article. We have thoroughly read all of your comments and suggestions.
The answers are listed in the same order as the comments and suggestions were:
Q1: In the 2.1 chapter it would be useful to give temperature range for annealing as stated later in the manuscript (I think only at p6)
A1: We have added the annealing temperature range in the 2.1 Methods subsection. Thank you for the suggestion.

Q2: Page 3, line 132 and 133: Möss specter should be changed to Möss spectrum
A2: We have made minor language corrections in the whole manuscript, thanks for your attentiveness.

Q3: line 146 I didnt understand how relative areas of the sextets corresponds well to site occupancies, especially it is not the case for M+A samples. Please, explain. Also there are strong disagreement about percentage of alpha iron from XRD and Mossbauer fit for M+A CNT samples. Discuss.
A3: Thank you for this valuable comment, we appreciate your thoughtful examination of the results. The applied Mössbauer spectroscopy method is sensitive to 57Fe isotopes exclusively. For example, the M+A CNT sample consisted of 70 % of Sm2Fe17Cx , 24% of α-Fe and  6% of Sm2O3 according to XRD analysis. The mass fraction of iron in the Sm2Fe17Cx phase is 54 %. Then, the fraction of iron in the Sm2Fe17Cx phase will constitute 68 %, and the fraction of iron in the α-Fe will constitute 32 %. The latter value corresponds with Mössbauer spectroscopy data when taking into account errors.

Q4: Did you collect Moss room T spectrum for graphite M and M+A samples? Are they similar to CNT?
A4: We appreciate your interest, the spectra were measured and they qualitatively coincided with that of CNT. We have added a corresponding remark in the Results section in order not to clutter the manuscript with data.

Q5: I was wondering if is it possible to find C in lattice sites, not only in interstitial sites?
A5: The formation of substitutional solid solution is possible. However, the lattice periods should decrease in this case that is not observed experimentally. Therefore, we have made a conclusion that carbon dissolved interstitially. Thank you for this important question, we have added the corresponding discussion to the Results and Discussions section.

Q6: There is a record of monoclinic C2/m structure, please see:
https://next-gen.materialsproject.org/materials/mp-1219267#crystal_structure
in comparison to
https://next-gen.materialsproject.org/materials/mp-1426/#crystal_structure
you have obtained. I would appreciate to hear your opinion.
A6: Thank you for the suggested C2/m crystal structure of Sm2Fe17 carbide. We tried fitting it for the experimental spectra, the description turned out less accurate than that for the R-3m structure. We consider C2/m to be a theoretical modification that was calculated by machine learning while the R-3m is a stable structure proven with experimental data.

We have substantially improved the content of our paper with the help of your comments and suggestions and highly appreciate for that.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Authors took the given comments well enough into account when revising the manuscript.