Temperature rescaling of Gilbert damping

[Peela baradwaj naidu]

Hello VAMPIRE Users,
Can anyone shed light on temperature rescaling of Gilbert damping? From what I understand VAMPIRE has inbuilt frameworks to rescale material properties like anisotropy to change as a function of simulation temperature although we set a constant number for these material parameters, I am wondering if VAMPIRE has a similar rescaling function for Gilbert damping as well. From what I understand through literature is that Gilbert damping can have strong dependance on temperature as shown in this paper here [1]. Additionally, if VAMPIRE doesn't have such framework how would one get started with defining time dependent Gilbert damping ?
Thank You.

[gabo...@gmail.com]

By Gilbert damping α, if you mean the material:damping-constant for LLG given in the VAMPIRE 7.0 manual [2] on page 63 (pdf page 64), that looks like it can only be specified as a constant value as far as I know.  Though, anyone is this group can correct me, if they know differently.

If doing separate simulations, you could likely make a shell script that the changes the material:damping-constant in the material file for the corresponding sim:temperature set in the input file.  That should be a way to simulate a temperature dependent damping, α(T).

By temperature rescaling, if you mean material:temperature-rescaling-exponent on page 71 (pdf page 72) of [2], that α looks to be different.  I think that's the exponent on (Texp/Tc)^α given in equation (9) of the article at [3] for Monte Carlo.

For material:damping-constant, it may be important to note that may not be the typical phenomenological damping constant α (i.e., "macroscopic" ).  Under section "4.0.1. Spin dynamics" in the article at [4] in equation (13) for the LLG has λ where it describes in more detail about it being a "microscopic" phenomenological damping constant.

The above is from a continuous integral viewpoint.  If you were going to implement that in code, you would change that over to solve the equation by discrete integration in order to perform as a numerical calcaulation.  When putting in Google search, the AI output seems to illustrate that well in a table:

Therefore, you would likely have to find and modify the LLG code, if you wanted to do time-dependent damping α(t).

The atomistic_llg_heun.cpp and micromagnetic_llg.cpp files for example seen at [5] maybe were you would have to start to look for trying to do something like that.

Hopefully that helps.

[2] https://vampire.york.ac.uk/resources/vampire-manual.pdf

[3] https://arxiv.org/abs/1409.7397v2

[4] https://doi.org/10.1088/0953-8984/26/10/103202

[5] https://github.com/richard-evans/vampire/tree/develop/src/micromagnetic

Kind Regards,

Gavin

VAMPIRE user

[Richard Evans]

Dear Peela,

Just to add to the discussion, the intrinsic temperature-dependent damping (eg for the 50 nm Py sample in the paper you linked) is included in the thermal fluctuations in VAMPIRE - you can calculate this using the effective damping program. More complex effects like surface damping are more difficult to deal with, and depends on the specific physics. I would say that this is an emergent property of the system, so it should be possible to include it naturally.

Cheers,

Richard

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