The paper reports the results of the synthesis and magnetic characterization of Ni nanotubes (NT) arrays together with complementary simulations results to help in the interpretation of the results.

The authors first present a facile synthesis route to produce the nanotube arrays, explaining in detail the different steps in the preparation conditions and the characteristic times need in each step. They prepare samples with NT of different ticknesses, that can be controlled by catodic reduction potential. This is an interesting achievement that will allow them to study the dependence of magntic properties on this parameter, which in other synthesis routes cannot be so easily manipulated. In a subsequent passivation step thet are able to demonstrate the formation of an oxide layer at the inner surface of the NT which will turn out to be relevant to understand the magnetic properties.

The magnetic characterization is performed by studying the hysteresis loops at room and low temperature (T= 10 K) for the four set of samples. I think that the presentation of these results needs further attention as there are some conclusions that are not easy to follow or not well sustained as they are written. Moreover Sec. 3.2 is plagued with incorrect syntax in some sentences that will need deep grammar revision. In the attached pdf, some of them has been pointed out as notes, but the list is not complete. As I detail in the comments below and the attached pdf, the presentation of the simulation model and results deserve further improvement. In particular, regarding the connection with experimental ones.

In conclusion, in my opinion, the manuscript cannot be accepted for publication in the present form. Major revision is needed and a second round of refereeing of the resubmitted manuscript will be needed before it can be recommended for publication in Nanomaterials.

Comments :

• Introduction is too long, giving too many details that are not really relevant in the context of the work presented here. Please, consider rewritting it so that is easier to follow.

• Consider a grammar revision in deep. I have highlighted some of the mistakes in the attached pdf, but the list is not complete.

• In page 11 , authors state that "Therefore, other interactions of a more significant effect have to be present in the analyzed systems and a first hint in this respect was provided by the hysteresis loops of the samples collected at 10 K and presented in Fig. 8."

• Line 338: the sentence "the blocking temperature for the exchange bias effect (TB)," makes an incorrect use of the concept of blocking teperature. By this, the authors are refering to the temperature at which the loop shift desappears call it T_0, but this has nothing to do with a blocking phenomenon. TB is related to the dynamics of the typical experimental observation times and can be higher or lower than T_0. Please amend this conceptual error by using a different name.

• Line 385: regarding the conclusiion of sentence "in contrast to the theoretical estimations presented in Fig. 7h." After reading the section up to this point, and seeing the authors statement, I cannot see then the point in performing simulations if they cannot support the experimental phenomenology. Authors should state more clearly the usefulness of the simulations within the context of their study and they should state more clearly also the conclusions from the simulation results. As the manuscript is written, it seems to me that none of the simulated results helps or give any insight on the experimental ones.

• An important ponit when comparing simuations to experimental results is that in the latter the NT have an oxide layer that, as far as I understood, is not included in the model. I think that this is a critical point. Could the authors elaborate further on this point?