Magnetization Dynamics in FexCo1-x in Presence of Chemical Disorder
Round 1
Reviewer 1 Report
The paper treats the basic magnon dispersion band and magnon damping coefficients for Fe-Co alloys. The magnon frequencies and spectral widenings are obtained via evaluating the Furier-transformed spin-spin correlation function and compared to the results of atomistic simulations of the Landau-Lifshitz-Gilbert dynamics. The method is interesting and the results are of importance for experimental measurements of material parameters.
However, several points require to be clarified. First, in formulation of the model, what value is taken by Delta parameter of the XXZ model applied? It is probably negligible within linear approximation applied since magnon-magnon scattering is stated to be omitted. If so, this should written explicitely. More importantly, confining the spin Hamiltonian to the XXZ model raises the question about the reason for neglecting the single-ion anisotropy of Fe-Co alloys, thus, to the correctness of the ASR calculations.
The comparison of ASR and ASD methods suffers from explicite conclusions. Which one is better and to what purposes? If I understand well, the comparison allows one for distinguishing between the correlation and hybridization effects in the magnon spectrum and its broadening. Unfortunately, Figs. 2(c) and 3(g) which are crucial for that comparison are cut and invisible in the given manuscript version.
There are many misprints in the text, e.g. in page 2: "The is similar.." instead "There is similar...". In page 9, first paragraph contains 7 consecutive statement initializing from "This" or "It is". Such a composition makes the paragraph not readable.
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Reviewer 2 Report
This manuscript presents a theoretical formulation of magnetization dynamics in disordered binary alloys based on Kubo linear response theory interfaced with the combination of density functional based tight-binding linear muffin-tin orbitals, generalized recursion and Augmented space formalism. This method is applied to study the magnetization dynamics in chemically disordered FexCo1-x (x = 0.2, 0.5, 0.8) alloys. The method is sound, the results are resonable and interesting. The writing and structure of the manuscript is nice. I suggest accept for publication in Magnetochemistry.
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Reviewer 3 Report
The authors have the lifetime and energy of the magnon in the bcc-FeCo alloy. They have been calculated by augmented space formalism (ASF) and atomistic spin dynamics (ASD). For example, significant magnon softening has been observed in Fe20Co80 at the boundary of the Brillouin zone. This knowledge is essential for the realization of new spintronics devices. We recommend the publication of this paper after revision for the following comments.
1. Because the Fe-Fe, Fe-Co, and Co-Co exchange parameters have different values, the FeCo alloys would have larger unit cell and smaller first Brillouin zone than Fe-bulk. The size of the unit cell and the number of atoms in the unit cell would be different for Fe20Co80 and Fe50Co50. However, the size of the Brillouin zone in the results of Figs. 2 and 3 is similar to that of bcc-Fe. The H-points of Fe20Co80 and Fe50Co50 and the H-points of bcc-Fe would all have different values of the wavenumber. Can the authors add a comment on the relationship between each symmetry point, wavenumber, and the first Brillouin zone? Can authors illustrate the unit cell used to calculate the magnons for FeCo alloys at x=0, 0.2, 0.5, 0.8?
2. On page 8, line 193, the authors wrote that The magnon softening is clearly visible in Fe20Co80 at the zone boundary. From which results did the authors conclude this? Please explain in more detail. Additionally, what is the value of q of the zone boundary?
3. On page 8, line 209, the authors wrote that the temperature is 0.1 K. How did the authors include the temperature in the ASD calculation? In section 2.4, the authors did not discuss the temperature. Please add about this.
4. On page 8, line 209, the system size is written as 120x120x120. Please add a dimension of 120.
5. On page 8, line 216, the authors wrote that "the softening of magnon spectra for Fe20Co80 alloy is similar to that obtained from ASR calculations shown above." From which results did the authors conclude this? Please explain in more detail.
Author Response
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Round 2
Reviewer 1 Report
I have received satisfacory author's response and I recommend publication of the manuscript
