Electrochemical Deposition of CoP and CoNiP as Hard Magnetic Scales in a Position Measurement System
Round 1
Reviewer 1 Report
This manuscript presents an as-plated process for hard magnetic Co-based material for application in magnetic scales of positioning systems with resolutions in the nanometer scale. The binary CoP process shows a suitable out-of-plane magnetization for be used as micro structured magnetic scale bars. This manuscript is well structured and written. However, authors could improve their manuscript considering the following comments:
1.-Introduction should add more recent references about investigations of magnetic material used in magnetic scales.
2.-Which are the main advantages and limitations of the proposed fabrication process with respect to other investigations reported in the literature?
3.-Authors should add discussion about mechanical reliability of the CoP films.
4.-Which are the main challenges to use the CoP films in magnetic scales?
5.-Authors could indicate the statistical data of the reported results.
Author Response
Reviewer 1
This manuscript presents an as-plated process for hard magnetic Co-based material for application in magnetic scales of positioning systems with resolutions in the nanometer scale. The binary CoP process shows a suitable out-of-plane magnetization for be used as micro structured magnetic scale bars. This manuscript is well structured and written. However, authors could improve their manuscript considering the following comments:
Answer: Thank you so much for the valuable comments and recommendations. We have included some more explanations and some literature in the reviewed version as described below.
1.-Introduction should add more recent references about investigations of magnetic material used in magnetic scales.
Answer: We have mentioned two more references concerning IC/CMOS compatible processes for fabricating magnetic material which are in principle suitable for magnetic scales.
- Reimer, F. Lofink, T. Lisec, C. Thede, S.Chemnitz and B. Wagner: Temperature-stable NdFeB micromagnets with high-energy density compatible with CMOS back end of line technology. MRS Advances, 2016, 1, 209-213. (DOI: 10.1557/adv.2015.19).
- Sharma, I. Radulov, M. Major, L. Alff: Evolution of Magnetic Anisotropy With Sm Contents in Sm–Co Thin Films. IEEE Transactions on Magnetics, 2018, 54(11). (DOI: 10.1109/TMAG.2018.2837006).
Furthermore, we have added related explanations in the introduction (s. also comment 2.)
2.-Which are the main advantages and limitations of the proposed fabrication process with respect to other investigations reported in the literature?
Answer: We have introduced the main aspects in the introduction as following:
“Thin film technologies such as sputtering and molecular beam epitaxy enable the deposition of thin magnetic films, e.g., Co-based or rare earth alloys such as SmCo with various magnetic anisotropy configurations. However, only relatively thin layers can be provided through these processes, which means that the effective magnetic field strength is usually too low at working distances typical for the respective application. Among the manufacturing processes for thick magnetic layers described in the literature, agglomeration of powder magnets by atomic layer deposition can be used to produce thick integrated micromagnets, with the drawback that the lower packing density requires the use of rare earths to achieve sufficiently high magnetic field strengths at a given distance. Electrochemical deposition of alloys, on the other hand, enables the cost-effective production of thick, integrated Co-based micromagnets with a high degree of geometric freedom and precision. A limitation of the application of this process is the small number of materials for which manufacturing processes exist.”
3.-Authors should add discussion about mechanical reliability of the CoP films.
Answer: We have added the following text:
“CoP and CoNi films offer the advantage that they can be deposited very homogeneously with respect to their microstructure. This is also evident with regard to their mechanical properties, such as hardness and indentation and Young’s modulus, respectively. With regard to hardness and elastic moduli, a dependence on the deposition temperature as well as the current density should be noted in particular, although this shows no influence on the homogeneity of the coatings. In addition to these factors, the coating thickness in particular is of decisive importance, as it fundamentally influences not only the mechanical properties but also the magnetic properties in particular. These phenomena have also been confirmed in own investigations. Due to the very good mechanical properties characterized by high hardness and very good wear and corrosion resistance, CoP films in particular will be a good alternative to hard chrome coatings in the future, already shown in Safavi et al. Environmentally safe process conditions can be used, allowing controlled deposition on various work pieces on a large scale, which is an important advantage over conventional hard chrome deposition.”
4.-Which are the main challenges to use the CoP films in magnetic scales?
Answer: We have added the following text:
“Another challenge with electrochemically deposited compact CoP and CoNiP thick films is to control the inherent mechanical strain so that crack-free micromagnets with good adhesion can be produced.”
5.-Authors could indicate the statistical data of the reported results.
Answer: The experiments shown in Fig. 2, 3 and 4 were performed with the rotating disc electrode to determine the influence of current density or fluidic conditions (here: rotational speed) on the phosphorus content and to determine the best working range for making the scales in terms of current density. Therefore, only one sample (one disc) per point was manufactured.
In our opinion a classical statistical evaluation (e.g. standard deviation for each point) was therefore not necessary as the results were significant enough to choose parameters for the further depositions of the scales and cannot be carried out due to the data (one disc/value per point).
Reviewer 2 Report
Ch.2.1 p 3
“For the CoP deposition a basic electrolyte according to [6] is used.”
The composition of the bath must be specified, I understand there is the reference, but the reader should be able to reproduce the experiment, which is the basis of science. Moreover, the following part of the text is devoted to illustrate the role of the different reagents, thus making a detailed description of the bath even more needed.
Few lines after: “phosphor ions.” Phosphor ions ??? this seems wrong, I m not aware of free P ions in solutions, what is supposed to be the relevant oxidation state ? I guess authors want to say hypophosphite anions due to the presence of sodium hypophosphite.
Few lines after: “A wetting agent and a grain refiner/stress reliever are essential to ensure 93 an error-free plating with low residual stresses.” Even here the detailed description is needed: chemicals and relevant concentration.
Ch.2.2 p 3
“A homogeneous magnetic field HFA is applied in the 129 out-of-plane direction (growth direction) during the electrochemical deposition using a 130 ferromagnetic material. Then the magnetic domains form in a way to reduce or avoid the 131 formation of an external magnetic stray field in an effort to remain in an energetically 132 stable state. The magnetic field was generated by three ferrite permanent magnets (10 × 133 15 × 2 cm³). Two magnets stacked together are placed right behind the cathode with 3 mm 134 distance between magnet surface and wafer and the other is placed behind the anode. 135 The anode/cathode gap is 16 cm.”
The description is not superclear, a figure would help.
Ch.2.2 p 4
Figure 2
Specify how the data have been obtained: I understand was a galvanostatic electrodeposition process, how much time ? it would be interesting to report the potential vs time curves (like supp info).
What methodology was used to measure the Cobalt content ?
P5 Figure 3 and 4 are impossible to read instead of black and dark blue, change to black and red. The legend must report in detail a description of the experiment.
Figure 8 p7. Legend: “The in-plane and out-of-plane measurements are supposed to be major and 219 minor loops, respectively.” Why “supposed” ? I think “supposed” it should be deleted.
Author Response
Reviewer 2
Answer: We thank the reviewer very much for the valuable and helpful questions and comments.
Ch.2.1 p 3
“For the CoP deposition a basic electrolyte according to [6] is used.”
The composition of the bath must be specified, I understand there is the reference, but the reader should be able to reproduce the experiment, which is the basis of science. Moreover, the following part of the text is devoted to illustrate the role of the different reagents, thus making a detailed description of the bath even more needed.
Few lines after: “phosphor ions.” Phosphor ions ??? this seems wrong, I m not aware of free P ions in solutions, what is supposed to be the relevant oxidation state ? I guess authors want to say hypophosphite anions due to the presence of sodium hypophosphite.
Few lines after: “A wetting agent and a grain refiner/stress reliever are essential to ensure 93 an error-free plating with low residual stresses.” Even here the detailed description is needed: chemicals and relevant concentration.
Answer: We have added a table and a sentence containing the composition of the electrolyte:
Table 1. Basic electrolyte
|
Chemical |
Concentration (mol L-1) |
|
|
Cobalt sulfate (CoSO4 6H2O) |
0.12 |
|
|
Sodium hypophosphite (NaH2PO2 2H2O) |
0.06 |
|
|
Boric acid (H3BO3) |
0.49 |
|
|
Sodium sulfate (Na2SO4) |
0.16 |
|
|
Sodium saccharin (C7H4NO3SNa2 H2O) |
0.01 |
|
“The CoNiP electrolyte is identical except the addition of 0.13 (mol L-1) nickel sulfate (NiSO4 6H2O).”
Ch.2.2 p 3
“A homogeneous magnetic field HFA is applied in the 129 out-of-plane direction (growth direction) during the electrochemical deposition using a 130 ferromagnetic material. Then the magnetic domains form in a way to reduce or avoid the 131 formation of an external magnetic stray field in an effort to remain in an energetically 132 stable state. The magnetic field was generated by three ferrite permanent magnets (10 × 133 15 × 2 cm³). Two magnets stacked together are placed right behind the cathode with 3 mm 134 distance between magnet surface and wafer and the other is placed behind the anode. 135 The anode/cathode gap is 16 cm.”
The description is not superclear, a figure would help.
Answer: Thank you for pointing this out. We have described the arrangement of the magnets more clearly. Hopefully this is easier to understand now.
“Field-assisted deposition is used to study the induction of an out-of-plane magnetic anisotropy. For this purpose, a homogeneous magnetic supporting field is applied perpendicular to the wafer plane (in-growth direction). This supporting field was generated by two ferrite permanent magnets (10 × 15 × 2 cm³). One of the magnets is placed directly behind the cathode with 3 mm distance between the magnet surface and the wafer and the other is placed behind the anode. The distance between anode and cathode is 16 cm.”
Ch.2.2 p 4
Figure 2
Specify how the data have been obtained: I understand was a galvanostatic electrodeposition process, how much time ? it would be interesting to report the potential vs time curves (like supp info).
What methodology was used to measure the Cobalt content ?
Answer: Thank you very much for this valuable questions. We have described the procedure leading to the results presented in Figure 2 in its subtitle and with the following text in Chapter 2.1. “The deposition was carried out in galvanostatic mode with a constant current applied. The deposition time to reach a theoretical thickness of 10µm was calculated via Faraday’s law assuming a current efficiency of 90%. The exact thickness of each disc varies depending on the real current efficiency.”
Further remarks: While we had a three electrode setup installed we carried out the depositions outlined in the manuscript in galvanostatic mode alone. We did not record the potential curve and only checked the initial potential to ensure stable initial conditions after the polishing of the discs.
The cobalt content in the CoP-layers has been measured by EDX. We calculated the Co content in the electrolyte from the original concentration and the amount of deposition during the experiments.
P5 Figure 3 and 4 are impossible to read instead of black and dark blue, change to black and red. The legend must report in detail a description of the experiment.
Answer: We have changed the color of all figures into black and red. We also have included the examination methods in the legend of the figures.
Figure 8 p7. Legend: “The in-plane and out-of-plane measurements are supposed to be major and 219 minor loops, respectively.” Why “supposed” ? I think “supposed” it should be deleted.
Answer: We have deleted “supposed to”.
Round 2
Reviewer 1 Report
This second version of manuscript has been improved considering the reviewer's comments.
