The Impact of Ho Addition on the Microstructural Features and Magnetic Performances of Sintered NdFeB Magnets

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

   The manuscript reports the study of the effect of grain boundary diffusion of Tb on the coercivity of sintered NdFeB-type magnets. The authors compared magnetic performance of two magnets, one of which was doped by holmium. Using XRD and SEM measurements they found that, in addition to Nd2Fe14B phase, fine precipitates of Ho2Fe14B phase appear in the Ho-doped magnet. The precipitates initiate refinement of the grains and facilitate diffusion of Tb within the magnet. The manuscript contains new information and can be published after the following points are considered.

1. As seen from Table 1, the compared samples contain different values of the rare earth (Nd+Ho): 28 wt.% for sample A and 31 wt.% for sample B. As a result, a larger amount of the grain boundary phase is observed by SEM images (compare (b0) vs. (a0) in Fig. 4). It is well-known that the coercivity depends on the amount of the grain boundary phase. What arguments can be given in favor of the fact that the increase in coercivity from 11.10 up to 12.54 kOe is associated with the introduction of holmium?
2. Section Materials and Methods should include the detailed information on sample preparation procedure. Usually, for grain boundary diffusion process for NdFeB magnet the diffusion path can reach up to 5 mm. What is the sample size used for magnetic measurements? How were SEM images taken at 50, 100 and 300 µm depth? Why XRD patterns were taken at the surface only?
3. Page 6, Line 250-251. In magnet B, the concentration of Ho inside the matrix grains is higher than that at the grain boundaries. This statement contradicts to Fig. 4c, according to which the grain boundary phase contains lager amount of Ho.
4. As seen from Fig. 5, the Tb concentration at 300 μm appears to be very small. Is it still high enough to create the core-shell structure responsible for the coercivity increase?
5. What is the reason why the solid solution (Nd,Ho)2Fe14B is not formed in the magnet B, while the (Nd,Tb)2Fe14B shell is formed?
6. In Fig. 5(a1,b1), the areas (structures) are marked as I, I, I. Is it correct?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have studied priston NdFeB doped with Ho, and starting materials have been subsequently studied for the Ta diffusion process. They have found an interesting and potentially technologically useful effect in the case of Ho samples, where better diffusion of  Tb is established and the anti-shell structure is removed.  Besides extensive structural analysis by using XRD, FESEM, and EPMA, the authors have also performed measurements of the coercivity field. They have found that adding Ho creates a higher coercivity field in NdFeB.

 

The paper deserves to be published in Magnetochemistry. My only objection is that the authors could give a more detailed description of the sample preparation procedure. It looks from the present description that it would be hard to accurately reproduce the experiment.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed all issues identified in the previous review report positively. The revised version of the manuscript is suitable for publication.