Investigation of Magnetocaloric Properties in the TbCo₂-H System

Round 1

Reviewer 1 Report

In this manuscript, the authors investigate the effect of hydrogenation on the magnetocaloric properties of TbCo2-H. The study is well designed and well implemented. I therefore recommend its acceptance for publication in its current form. 

Author Response

Thank you for your detailed analysis of our work.

Reviewer 2 Report

Manuscript number: crystals-2051847 Crystals MDPI (type of the paper: Article, Section: Crystalline Metals and Alloys; Special Issue Intermetallic Compound (Volume II))

 

TITLE: Investigation of magnetocaloric properties in the TbCo2-H system

 

AUTHORS: Galina Politova, Irina Tereshina, Ioulia Ovchenkova, Abdu-Rahman Aleroev, Yurii Koshkid'ko, Jacek Ćwik, Henryk Drulis

 

 

The first review of the manuscript

 

 

Overall description of the manuscript

 

 

In the manuscript entitled “Investigation of magnetocaloric properties in the TbCo2-H system” authored by Galina Politova, Irina Tereshina, Ioulia Ovchenkova, Abdu-Rahman Aleroev, Yurii Koshkid'ko, Jacek Ćwik, Henryk Drulis, the authors present experimental investigations of properties of TbCo2 with addition of hydrogen. They presents X-ray diffraction patters obtained for characterization of the samples, which confirms that they are clean and contains one phase. Next, the results of magnetization measurements (as a function of magnetic field for fixed temperature). From these analyses (magnetization isotherms M(B) for different temperatures) the authors determine the magnitude of the magnetocaloric effect by indirect method for different fields. Finally, they presents discussion of critical exponents for detailed analysis of the nature of the magnetic phase transition in studied materials. The section “Materials and methods” clearly describes how the samples were prepared and measurements, what make the results reproducible by other groups. Nevertheless, unfortunately, the manuscript does not look like comprehensive and systematic studies of magnetic (in particular, of magnetocaloric effect) in studied compound with changing of the hydrogen included (effects of interstitial atoms of the TbCo2 compound).

 

The manuscript more or less fits the journal scope. The English language in the manuscript is very good. The paper has 10 pages and includes 43 references (equivalent to 2 pages), 6 figures (about 2), and 1 Table (1/2 page) – effectively about 5 pages of the main text (not counting abstract and the title). The diagrams (figures) are clear, they are essential and their captions are informative. The title clearly and concisely conveys the topic of the article. The abstract quite well describes the content of the manuscript. The findings look correctly. The discussion and conclusions are supported by the results.

 

However, I read the manuscript very carefully and, unfortunately, I cannot recommend publication of the manuscript in the present form. I have several issues, which require some improvement, additions or justifications.

 

 

Specific comments to the authors:

 

1) It is not clearly stated which sample of TbCo2Hx were obtained by authors. For example in Figure 1 they present results for x=0 and x=2.4, but on page 3 (line 114) the write about samples with x=0, 0.5, 2.4 (“X-ray diffraction analysis (see Fig.1) showed that in all the obtained TbCo2Hx (x = 0, 0.5, 2.4) compounds”). Figures 2, 4, and 6 presents data for x=2.4, but in Figure 3 we have data for x=0, x=2.0, x=2.4, x=3.9. In addition in Fig. 5(a) data for x = 2.43 (label in the figure, probably it should be x=2.4) are shown and in Fig. 5(b) the data for x=0 and x = 0.5 are presented. I understand the mainly data for x=2.4 are presented in the manuscript, but it should be commented and justified. And also it should be clearly mentored which samples (with which values of x) were investigated by the authors.

 

2) In addition, it is surprising for me, that there is no data for x=0.5 in Figure 3. What is the reason? The authors presents data for x=0.5 in Figure 5b, so they probably performed also measurement of the Curie temperature. Why the data presented for x=2.4 and x=0.5 in Figure 5 are not the data for the same quantities? In particular, why the temperature change of the sample during the adiabatic increase in the magnetic field is only shown for x=0.5? I thought that the main aim of the paper is investigation of the change of x on the magnetocaloric effect in the studied materials so probably  data for $\Delta S$ and $\Delta T_{ad}$ should be presented for all samples. From the presented data, the reader cannot have full picture of the evolution of the investigated properties with changing x. The presented data looks like the studies were not systematic.

 

3) The results of the analysis of the critical exponents is presented only for x=2.4. Why similar analysis were not performed for other x and collected for example in Table 1. I wonder to know if the similar measurements presented for x=2.4 in, e.g., Figures 1, 2, and 4) were performed for other samples? In particular, how were the points in Figure 3 for x=2.0 and x=3.9 determined (i.e., the Curie temperature for these values of x)? Please modify.

 

4) If the data for x=0 we not obtained by the authors (like they indicate in Table 1), from which reference they took its Curie temperature? This temperature is important for the other points in Figure 3. It is not indicated even on page 2 (line 66), where the temperature is given. On the other hand, the authors claim that they also obtained the sample with x=0, so why their results are not presented for the comparison (particularly, in Table 1)? Please explain.

 

5) Any abbreviation or acronym should be defined in the place, where it is used for the first time (separately in the abstract and the main text). In particular, MCE is not explained in the abstract, which should be self-explanatory. Please revise the manuscript accordingly.

 

6) I found some minor typos which should be corrected, e.g., the-data (extra hyphen) (page 3, line 125); extra coma and dot next to $T_mid$ (page 5, line 177), “measu red” – extra space (page 6, line 185, caption of Figure 5), Tc in Eq. (4) – “c” should be in the lower index, “J. of Phys.: Conference Series” should be “J. Phys. Conf. Ser.” (page 9, line 315, Ref. [14]”, “Acta Physica Polonica A” should be “Acta Phys. Pol. A” (page 9, line 335, Ref [25]), “J. Alloys and Compounds” should be “J. Alloys Compd.” (page 10, line 355, Ref. [36]), “Journal of the Physical Society of Japan” should be “J. Phys. Soc. Jpn.” (page 10, line 362, Ref [39]). Please revise the text carefully with attention for proper formatting of references.

 

In my opinion, the manuscript cannot be published in the present form. The crucial points  are points 1)- 4) mentioned above. Nevertheless, I strongly believe this paper is might be suitable for publication in “Crystals” MDPI journal as an regular article. The topic of the paper, which is strongly associated with interesting magnetic materials, can attract a lot of attention (because of their potential applications in sensors and magnetic devices) and can be interesting for some groups of scientists.

Author Response

Thank you for such a detailed analysis of our work, carried out by you. We tried to answer all your questions and made the necessary changes to our article.

1) It is not clearly stated which sample of TbCo2Hx were obtained by authors. For example in Figure 1 they present results for x=0 and x=2.4, but on page 3 (line 114) the write about samples with x=0, 0.5, 2.4 (“X-ray diffraction analysis (see Fig.1) showed that in all the obtained TbCo2Hx (x = 0, 0.5, 2.4) compounds”). Figures 2, 4, and 6 presents data for x=2.4, but in Figure 3 we have data for x=0, x=2.0, x=2.4, x=3.9. In addition in Fig. 5(a) data for x = 2.43 (label in the figure, probably it should be x=2.4) are shown and in Fig. 5(b) the data for x=0 and x = 0.5 are presented. I understand the mainly data for x=2.4 are presented in the manuscript, but it should be commented and justified. And also it should be clearly mentored which samples (with which values of x) were investigated by the authors.

Thanks for the important note.

In the work, we obtained samples with x=0, 0.5, 2.4, i.e. with high and low hydrogen content. Samples with x=0 and 0.5 could be obtained in the cast state and studied by the MCE by the direct method. The sample x=2.4 turned out to be in the form of a powder, so it was possible to study the MCE for it only by an indirect method.

In the work of Mushnikov [30], the magnetic properties of TbCo2Hx samples with x = 0, 0.7, 2, 2.4, 3.9 were obtained and investigated. The magnetic moment at Co atoms and the Curie temperature were found to exhibit an increase at low hydrogen contents, whereas at high hydrogen contents, both magnetic characteristics decrease substantially. MCE was not studied in TbCo2-H system. It is also known [32] that high MCE values for RCo2 compounds with a Laves phase structure are achieved only at temperatures below 200 K. Therefore, new compositions with Tc less than 200 K are of particular interest.

Necessary additions have been made to the sections Introduction and Materials and methods. Necessary corrections have also been made to the Figures.

 

2) In addition, it is surprising for me, that there is no data for x=0.5 in Figure 3. What is the reason? The authors presents data for x=0.5 in Figure 5b, so they probably performed also measurement of the Curie temperature. Why the data presented for x=2.4 and x=0.5 in Figure 5 are not the data for the same quantities? In particular, why the temperature change of the sample during the adiabatic increase in the magnetic field is only shown for x=0.5? I thought that the main aim of the paper is investigation of the change of x on the magnetocaloric effect in the studied materials so probably  data for $\Delta S$ and $\Delta T_{ad}$ should be presented for all samples. From the presented data, the reader cannot have full picture of the evolution of the investigated properties with changing x. The presented data looks like the studies were not systematic.

 

The main purpose of this paper is to present our data by focusing on TbCo2H with high hydrogen content, comparing and analyzing them with already known literature data, when possible (for example, for the analysis of Tc). Data for x = 0.5 has been added to Figure 3, and a corresponding description is given in the text.

 

3) The results of the analysis of the critical exponents is presented only for x=2.4. Why similar analysis were not performed for other x and collected for example in Table 1. I wonder to know if the similar measurements presented for x=2.4 in, e.g., Figures 1, 2, and 4) were performed for other samples? In particular, how were the points in Figure 3 for x=2.0 and x=3.9 determined (i.e., the Curie temperature for these values of x)? Please modify.

 

At present, it is impossible to determine the critical parameters for all known hydrides due to the difficulty of obtaining them in a single-phase state.

To determine the Curie temperatures for x=2.0 and x=3.9, we analyzed the course of the temperature dependences of the magnetization, taken from the work of Mushnikov. To determine the Curie temperatures for the TbCo2-H system, we used also inflection point technique based on analysis of the behavior of the temperature dependences of the magnetization in magnetic field [30].

Table 1 contains our data on the initial sample, which are in good agreement with the literature data. The critical values for our composition x=2.4 are compared with those of other substituted compositions, since there are no data for hydrides.

 

4) If the data for x=0 we not obtained by the authors (like they indicate in Table 1), from which reference they took its Curie temperature? This temperature is important for the other points in Figure 3. It is not indicated even on page 2 (line 66), where the temperature is given. On the other hand, the authors claim that they also obtained the sample with x=0, so why their results are not presented for the comparison (particularly, in Table 1)? Please explain.

 

Thank you for your comment. We unconditionally obtained the TbCo2 initial compound  and did structural and magnetic studies for it. The data obtained from this sample were in good agreement with the literature data, and therefore, in our article, we focused on the work of other authors in order to emphasize the priority of their work. We added the data we obtained for the TbCo2 initial compound to the table and figures.

 

5) Any abbreviation or acronym should be defined in the place, where it is used for the first time (separately in the abstract and the main text). In particular, MCE is not explained in the abstract, which should be self-explanatory. Please revise the manuscript accordingly.

 

Thank you for your comment, we have edited the text accordingly.

 

6) I found some minor typos which should be corrected, e.g., the-data (extra hyphen) (page 3, line 125); extra coma and dot next to $T_mid$ (page 5, line 177), “measu red” – extra space (page 6, line 185, caption of Figure 5), Tc in Eq. (4) – “c” should be in the lower index, “J. of Phys.: Conference Series” should be “J. Phys. Conf. Ser.” (page 9, line 315, Ref. [14]”, “Acta Physica Polonica A” should be “Acta Phys. Pol. A” (page 9, line 335, Ref [25]), “J. Alloys and Compounds” should be “J. Alloys Compd.” (page 10, line 355, Ref. [36]), “Journal of the Physical Society of Japan” should be “J. Phys. Soc. Jpn.” (page 10, line 362, Ref [39]). Please revise the text carefully with attention for proper formatting of references.

Thanks, corrections made.

Reviewer 3 Report

The research topic is quite interesting. The presentation and discussion of the content meet the requirements of the journal. I estimate that their manuscript is now ready for publication.

Author Response

Thank you for your detailed analysis of our work. 

Reviewer 4 Report

Dear Authors,

 In this work the MCE in the region of the Curie temperature was studied both by direct and indirect methods in external magnetic fields. The authors have paid special attention to the magnetic and magnetothermal properties of the hydro- gen-containing TbCo2–H system. The mechanisms responsible for the change in the Curie temperature were established, and the field and temperature dependences of the magneto- caloric effect were analyzed in detail. Additionally, the magnetocaloric properties for various systems according to the TbCo2 compound were compared. Generally, the manuscript  presented acceptable results in the field; however, it needs some minor revisions before publication.

-The abstract needs basic modification. It is recommended to rewrite the abstract. It should be a reflection of all sections of the manuscript.

-There are some English Language errors in the manuscript that should be addressed.

-Conclusion should present important achievements of the study. It should be rewrite to present the significance of the study. It may be presented using bullet points.

-Introduction should be extended. Further updated references should be used in the section.

-References should be updated. There are many old ones in this section. It is recommended to use more updated references from the journal.

 Regards

Author Response

Dear Reviewer,

I'm sorry that this happened, that you received an answer in Russian. It seems that somewhere when inserting text into forms, an auto-translator into Russian worked. I'm trying to fix it).

Thanks for the detailed analysis of our work.

We have tried to make the changes recommended by you to the abstract, introduction and conclusion:

-The abstract needs basic modification. It is recommended to rewrite the abstract. It should be a reflection of all sections of the manuscript.

Abstract corrected

-There are some English Language errors in the manuscript that should be addressed.

We have tried to eliminate errors in the language.

-Conclusion should present important achievements of the study. It should be rewrite to present the significance of the study. It may be presented using bullet points.

The conclusion was rewritten according to your recommendations.

-Introduction should be extended. Further updated references should be used in the section.

The introduction has been extended and supplemented with references.

-References should be updated. There are many old ones in this section. It is recommended to use more updated references from the journal.

Recent references added.

Round 2

Reviewer 2 Report

Manuscript number: crystals-2051847 Crystals MDPI (type of the paper: Article, Section: Crystalline Metals and Alloys; Special Issue Intermetallic Compound (Volume II))

 

TITLE: Investigation of magnetocaloric properties in the TbCo2-H system

 

AUTHORS: Galina Politova, Irina Tereshina, Ioulia Ovchenkova, Abdu-Rahman Aleroev, Yurii Koshkid'ko, Jacek Ćwik, Henryk Drulis

 

 

The second review of the manuscript

 

 

In the revised version of the manuscript entitled “Investigation of magnetocaloric properties in the TbCo2-H system” authored by Galina Politova, Irina Tereshina, Ioulia Ovchenkova, Abdu-Rahman Aleroev, Yurii Koshkid'ko, Jacek Ćwik, Henryk Drulis, the authors included some modification and improvements according the Referees’ comments, which made the manuscript better and more clear for the reader. I have one minor comments.

 

In the reply for my comment point 3) from the previous report, the authors wrote “To determine the Curie temperatures for x=2.0 and x=3.9, we analyzed the course of the temperature dependences of the magnetization, taken from the work of Mushnikov. To determine the Curie temperatures for the TbCo2-H system, we used also inflection point technique based on analysis of the behavior of the temperature dependences of the magnetization in magnetic field [30].” In such a case, in my opinion, the reference [30] should be also mentioned in the caption of Figure 3, where only Refs. [38] and [39] are mentioned currently. This discrepancy should be removed.

 

In my opinion, based on the content and the scientific value, the manuscript can be published in the present form including the modification mentioned. I strongly believe this paper is suitable for publication in “Crystals” MDPI journal as an regular article in the Special Issue Intermetallic Compound (Volume II). The topic of the paper, which is strongly associated with interesting magnetic materials, can attract a lot of attention (because of their potential applications in sensors and magnetic devices) and can be interesting for some groups of scientists.

Author Response

Thank you for your comment! The required reference [30] is added to the figure caption.