Spin-Topological Electronic Valve in Ni/hBN–Graphene–hBN/Ni Magnetic Junction

Round 1

Reviewer 1 Report

Wicaksono et al. conducted spin-polarized DFT calculations on junction device structures of the type Ni/hBN–graphene–hBN/Ni. The authors investigated twelve different stacking configurations and analyzed their impact on the electronic and magnetic structure. The configuration structures were based on anti-parallel (APC) and parallel (PC) states and differed in terms of overall energy. The authors further classified the stacking configurations into three groups depending on their relative energy.

Group I (least favourable) - The magnetic proximity effect from B atoms has a small impact on graphene's chiral symmetry. Group II - Configurations exhibit a wide mass-gapped Dirac cone in the spin majority channel due to the influence of the Ni surface state. Group III (most favourable) - Graphene's C atoms are affected by both upper and lower Ni slab surface states, resulting in a noticeable mass gap in the APC state and varying gaps in the PC state.

By mapping the spin LDOS, the authors demonstrate the potential use of the device as a topological/mechanical electronic valve.

Overall, the work is well-written and easy to follow. However, there are two minor remarks and one suggestion:

1. The term "mechatronics" used by the authors is misleading, as it does not relate to robots. Instead, the more appropriate term for such devices is "topological electronics." (Reference: https://pubs.rsc.org/en/content/articlelanding/2020/cs/c9cs00893d)

2. Suggestion: It may be advantageous for the authors to include clear multi-stack diagrams from both side and top views, showing the different layering configurations of their devices from a structural perspective.

3. Please provide geometries, preferably in CIF, POSCAR, or CELL file formats, of all studied configurations as supporting information files.

Author Response

We would like to thank reviewer 1 for his/her important question and suggestion. Here are our responses for each point of review:

Point 1:

The term "mechatronics" used by the authors is misleading, as it does not relate to robots. Instead, the more appropriate term for such devices is "topological electronics." (Reference: https://pubs.rsc.org/en/content/articlelanding/2020/cs/c9cs00893d)

Response:

We would like to thank reviewer 1 for the suggestion. As suggested, we replaced the "spin-mechatronic valve" terminology with "spin-topological electronic valve" in the revised manuscript.

Point 2:

Suggestion: It may be advantageous for the authors to include clear multi-stack diagrams from both side and top views, showing the different layering configurations of their devices from a structural perspective.

Response:

We would like to thank reviewer 1 for the suggestion. We added the clear multi-stack diagram in the "Supplementary Information" file as Figure S1.

Point 3:

Please provide geometries, preferably in CIF, POSCAR, or CELL file formats, of all studied configurations as supporting information files.

Response:

We would like to thank reviewer 1 for the suggestion. We added the crystal structure detail in the "Supplementary Information" file as Tables S1-S4.

By adding the Supplementary Information and omitting the misleading term of mechatronics, we hope our revised version will be sufficient for publication.

Reviewer 2 Report

The manuscript represents a very detailed theoretical and computational study a multilayer Ni/hBN–graphene–hBN/Ni heterostructure with various stacking configurations and different relative directions of the magnetization in Ni layers. The main emphasis is put on the magnetic proximity effect on the electronic structure and especially on the formation of the band gap in the Dirac spectrum. Such heterostructures are of interest from the viewpoint of the possible large magnetoresistance effect and provide an opportunity of fine tuning the band gap. The manuscript provides a comprehensive picture of possible configurations and the related physical effects in such heterostructures with a special focus on spintronic applications. The performed analysis appears to be novel and important, and it is of interest for many researchers dealing with magnetic junctions. Therefore, I would recommend the manuscript for publication in the Magnetochemistry journal.

However, it seems to me reasonable to clarify several issues.

1. The role of hBN layer should be discussed in more detail: whether it serves as a simple spacer for revealing the proximity effect or its role is more important.

2. In the very detailed analysis of 12 stacking configurations divided into three groups, it is rather difficult to understand what configuration corresponds to the ground state, and whether the tunneling between different configurations is possible.

3. In the description of the suggested application of the structures under study for a spin mechatronic valve, it is not clear what potential barriers it is necessary to overcome in the relative motion of the layers and what is the order of magnitude of the forces needed for such motion.

Author Response

We would like to thank reviewer 2 for his/her important questions. Here are our responses for each point of review:

Point 1:

The role of the hBN layer should be discussed in more detail: whether it serves as a simple spacer for revealing the proximity effect or its role is more important.

Response:

We would like to thank reviewer 2 for pointing out this important point. We added the following explanation in the last paragraph of "1. Introduction" in the revised manuscript:

"The hBN is a very important spacer in this system due to its insulator nature (huge band gap) and one atomic layer thickness which optimizes the propagation of surface state in creating a proximity effect on graphene. Its huge band gap also has little effect on the graphene's Dirac cone, so the electronic Dirac properties of graphene were solely controlled through the proximity effect. Additionally, the weak van Der Waals bonding formed between graphene and hBN creates easy controllability on the mechanical translation of the system."

Point 2:

In the very detailed analysis of 12 stacking configurations divided into three groups, it is rather difficult to understand what configuration corresponds to the ground state and whether tunneling between different configurations is possible.

Response:

We would like to thank reviewer 2 for pointing out this important point. We revised the first paragraph of section 3.1 by emphasizing the ground state among those three groups by referring to their total energy. Furthermore, at room temperature, each configuration has van Der Waals interaction/bonding between hBN and graphene, which hold their respective configuration and prevent it from tunneling. The changes between configurations are applicable only when the external perturbation is introduced.

Point 3:

In the description of the suggested application of the structures under study for a spin mechatronic valve, it is not clear what potential barriers it is necessary to overcome in the relative motion of the layers and what is the order of magnitude of the forces needed for such motion.

Response:

We would like to thank reviewer 2 for pointing out this important point. We added the following explanation in section 3.6 in the revised manuscript:

"Additionally, Since the van Der Waals bonding difference between each group configuration is so small, in the range of 50 - 70 meV where it is in the order of 10^-21 Nm, it is reasonable to have translation motion between two different configurations of two different groups."

By addressing each point of the question and making a revision based on it in the revised manuscript, we hope our revised version will be sufficient for publication.

Reviewer 3 Report

Journal: Magnetochemistry

Manuscript ID: magnetochemistry 2330551

Manuscript Type: Research Article

Manuscript Title: The importance of the interface in a Ni/hBN-graphene-hBN/Ni magnetic

junction on the graphene Dirac cone control for spin-mechatronics device  

Minor Comments:

1.     Title: The title requires minor amendment. Avoid using two similar words, i.e., ‘with’ in the title.  The title of this manuscript does not portray the significance of this research work. The title used is lengthy, consists of 19 words. Additionally, avoid using similar words repeatedly, i.e., “the” in the title.  there are many “the” words in the title, up to three times.  

2.     Abstract and Introduction: What is the novelty of this study? The novelty was not highlighted well for this study, in both abstract and introduction section. What is the importance of first-principles investigation? This needs to be highlighted as well.

3.     Introduction: The recent references (2020-2022) are from the authors. Please include more recent references from other group of researchers who conducted similar works and bridge the research gaps with previous researches.

4.     Conclusion: This section is too lengthy. The main outcomes from this research were not brought up concisely.

5.     Mechanist aspect: Usage of capital and lower-case letters were mixed-up in the manuscript. Please check the manuscript thoroughly.

6.     References: It is notified that the cited recent references (2020-2022) are from the authors. Please include more recent references from other group of researchers who conducted similar works.

7.     English problem: I suggest the authors to check the English language by native English speakers. There are grammatical mistakes spotted throughout the manuscript.

In general, the authors have attempted to study and conducted the first-principles study of the interface in a Ni/hBN-graphene-hBN/Ni magnetic junction on graphene Dirac cone control for spin-mechatronics device applications. However, novelty of this study needs to be strengthened. Therefore, the authors are required to make substantial improvement for this manuscript according to the points given above.

Author Response

We would like to thank reviewer 3 for his/her important questions. Here are our responses for each point of review:

Point 1:

Title: The title requires minor amendment. Avoid using two similar words, i.e., ‘with’ in the title.  The title of this manuscript does not portray the significance of this research work. The title used is lengthy, consists of 19 words. Additionally, avoid using similar words repeatedly, i.e., “the” in the title.  there are many “the” words in the title, up to three times.  

Response:

We would like to thank reviewer 3 for suggesting the implication of the title and improvement to increase the significance of the manuscript. We revised our title as follows by following the suggestions of reviewers 1 and 3:

"Spin-topological electronic valve in Ni/hBN-graphene-hBN/Ni magnetic junction"

Point 2:

Abstract and Introduction: What is the novelty of this study? The novelty was not highlighted well for this study, in both abstract and introduction section. What is the importance of first-principles investigation? This needs to be highlighted as well.

Response:

We would like to thank reviewer 3 for suggesting an improvement in the abstract and introduction to highlight the novelty of the research. We revised the abstract and introduction by emphasizing the novelty of this study on the findings of the spin-topology electronic valve and its possible application to create three or more non-volatile memory states that cannot be found in conventional magnetic junctions.

For the abstract, we revised the manuscript by revising the abstract to be followed:

"A spin-topological electronic valve was discovered in a Ni/hBN--graphene--hBN/Ni magnetic junction to control the in-plane conductance of graphene. By manipulating the mass-gapped Dirac cone (MGDC) of graphene's topology using the magnetic proximity effect, the spin-topological electronic valve was made possible. The first-principles investigation was conducted to show how the mechanism of graphene's MGDC is controlled. Twelve stacking configurations for the anti-parallel configuration (APC) and parallel configuration (PC) of the magnetic alignment of Ni slabs were calculated using spin-polarized density functional theory. Three groups can be made based on the relative total energy of the 12 stacking configurations, which corresponds to a van der Waals interaction between hBN and graphene. Each group exhibits distinctive features of graphene's MGDC. The configuration of the Ni(111) surface state's interaction with graphene as an evanescent wave significantly impacts how the MGDC behaves. By utilizing the special properties of graphene's MGDC, which depend on the stacking configuration, a controllable MGDC using mechanical motion was proposed by suggesting a device that can translate the top and bottom Ni(111)/hBN slabs. By changing the stacking configuration from Group I to II and II to III, three different in-plane conductances of graphene were observed, corresponding to three non-volatile memory states. This device opens the insight to MJs having three or more non-volatile memory states that cannot be found in conventional MJs."

For the introduction, we revised the manuscript by adding the following explanation at the beginning and end of the last paragraph of the introduction:

"In this study, we present a spin-topological electronic valve in Ni/hBN--graphene--hBN/Ni magnetic junction to control the IMR of graphene. The spin-topological electronic valve can be realized by controlling the topological nature of graphene's mass-gapped Dirac cone (MGDC) through the magnetic proximity effect. A first-principles study in which the magnetic proximity effect of the Ni surface state was used to control the pseudospin of graphene is proposed to understand the mechanism of a spin-topological electronic valve. ..."

and

"... By changing the stacking configuration from one group to another, three different in-plane conductance of graphene was observed, corresponding to three non-volatile memory states. This device opens the insight into magnetic junctions having three or more non-volatile memory states that cannot be found in conventional magnetic junctions."

Point 3:

Introduction: The recent references (2020-2022) are from the authors. Please include more recent references from other group of researchers who conducted similar works and bridge the research gaps with previous researches.

Point 6:

References: It is notified that the cited recent references (2020-2022) are from the authors. Please include more recent references from other group of researchers who conducted similar works.

Combined response for points 3 and 6:

We would like to thank reviewer 3 for suggesting an additional reference from other groups conducting similar research. In the last second paragraph of the introduction, we added the following statement in the revised manuscript:

"Recent studies reported that by considering a van der Waals heterostructure of graphene sandwiched with other 2D materials, the MGDC of graphene can be controlled through a proximity effect by twisting [28,29] the interface or giving strain to graphene [30]. "

And add references [28-30] in the references section.

Point 4:

Conclusion: This section is too lengthy. The main outcomes from this research were not brought up concisely.

Response:

We would like to thank reviewer 3 for suggesting an improvement of the conclusion to make it more concise. We revised the conclusion to be more concise as follow:

"In this study, we proposed a spin-topological electronic valve in Ni/hBN--graphene--hBN/Ni magnetic junction to control the in-plane conductance of graphene. The spin-topological electronic valve can be realized by controlling the topological nature of graphene's MGDC through the magnetic proximity effect. The first-principles investigation was conducted to show how the mechanism of graphene's MGDC is controlled. Twelve stacking configurations were proposed with two magnetic configurations on upper and lower Ni slabs, APC and PC. The 12 stacking arrangements were divided into three groups based on their relative total energy. Group I included configurations with a total energy range of 0--2 meV, with HC1B--BC2H and HC1H--BC2B having the lowest total energy. Group II included configurations with a total energy range of 55--65 meV, such as HC1N--BC2H, BC1B--NC2H, HC1H--NC2B, and HC1B--NC2N. Group III consisted of stacking configurations with relative total energies between 100 and 130 meV. The study found that the properties of graphene's MGDC in Group I depended on the arrangement of the upper and lower B atoms. When the arrangement of B atoms is asymmetric, the MGDC is able to open and close in APC and PC states, respectively. On the other hand, when the arrangement of B atoms is symmetric, the MGDC remains open for both APC and PC states. Nevertheless, a relatively small gap in the MGDC was observed in Group I. In Group II, the Ni surface state directly affected the mass-gapped Dirac cone of graphene, resulting in a wider gap of MGDC in the spin majority channel. However, since only one part of the Ni surface state, either from the upper or lower slab, affected one of the graphene sublattices, both APC and PC states resulted in an open MGDC. In Group III, the upper and lower Ni slab surface states affected both C atoms sublattices of graphene. In the APC state, a noticeable mass gap was observed for both asymmetric and symmetric cases, with the spin majority and minority channels overlapping. On the other hand, when the PC state is considered, a symmetric arrangement shows one of the spin channels has a larger mass gap than in Group II, while another spin channel has a relatively smaller mass gap. However, the chiral symmetry is preserved in the PC state in the asymmetric case, producing a spin-polarized Dirac cone. By utilizing the unique properties of graphene's MGDC in Ni/hBN--graphene--hBN/Ni magnetic junction, which depends on the stacking configuration, a controllable MGDC using mechanical motion can be proposed by suggesting a device that can translate the top and bottom Ni(111)/hBN slabs. This can be realized by considering an APC state on Ni/hBN--Gr--hBN/Ni and changing its configuration from HC1B--BC2H to BC1B--NC2H followed by BC1B--NC2H to BC1N--NC2B. Three different in-plane conductance of graphene was observed, corresponding to three non-volatile memory states. This device opens the insight into magnetic junctions having three or more non-volatile memory states that cannot be found in conventional magnetic junctions. "

Point 5:

Mechanist aspect: Usage of capital and lower-case letters were mixed-up in the manuscript. Please check the manuscript thoroughly.

Point 7:

English problem: I suggest the authors to check the English language by native English speakers. There are grammatical mistakes spotted throughout the manuscript.

Combined response for points 5 and 7:

We would like to thank reviewer 3 for pointing out some grammatical errors in the manuscripts. To address this problem, we asked an English editing service to check the grammar error in our manuscript, and the result of the correction has been implemented in our revised manuscript.

By addressing each point of the question and making a revision based on it in the revised manuscript, we hope our revised version will be sufficient for publication.