Question for Tc calculation with ferrimagnetism material

[lei qiao]

Hello everyone,

I'm simulating Tc of a 3D ferrimagnetism material. There are 12 atoms (first 8 are spin up and last 4 are spin down). Here I set the initial spin direction, (001) for first 8 and (00-1) for last 4. The results are very good except for the low temperature region data.

Please see the 2 figures, the curve is perfect for temperatures above 40K, but the data is clearly wrong at low temperatures. I also tried using the default initial spin direction (001), but the result is the same. I can't understand what is the reason for this?

I have also attached my input files, which may be helpful for your analysis.

Many thanks to you!

Lei

[lei qiao]

I'm using Version 5.0.0, and when I set initial-spin-direction=false as that in manual, Vampire give me an error which indicate initial-spin-direction must be three values.

[gabo...@gmail.com]

Sorry, I don't know the cause of your low temperature problem.  Maybe one of the others in the list will respond later, if they have experienced the issue.

It does look interesting, however, that you defined material[1], material[2], ..., and material [12] in your Co.mat file, whereas it looks like the entire structure uses only the material[1] as it is being set with mat_id 0 for all atoms in your file.ucf:

# ... id cx cy cz mat cat hcat:
0    0.000000000    0.333332981    0.496120977    0    1    0    
1    0.499999989    0.833333020    0.496120977    0    1    0    
2    0.500000005    0.166667000    0.503879023    0    1    0    
3    0.000000000    0.666666980    0.503879023    0    1    0    
4    0.000000000    0.333332981    0.003879000    0    1    0    
5    0.499999989    0.833333020    0.003879000    0    1    0    
6    0.500000005    0.166667000    0.996121011    0    1    0    
7    0.000000000    0.666666980    0.996121011    0    1    0    
8    0.000000000    0.333332981    0.250000000    0    1    0    
9    0.499999989    0.833333020    0.250000000    0    1    0    
10    0.500000005    0.166667000    0.749999983    0    1    0    
11    0.000000000    0.666666980    0.749999983    0    1    0

Kind Regards,

Gavin

VAMPIRE user

[gabo...@gmail.com]

The initial-spin-direction can specified in the mat file as a vector or as a bool flag.

If a vector, the spin can be set in a direction such as (100):

material[1]:initial-spin-direction=1,0,0

The initial-spin-direction could instead be set randomly by using a bool flag, where random is currently the only valid flag for that.

If you look at rocksalt.mat [1], you can see in that example it is used as:

material[2]:initial-spin-direction=random

[1] https://github.com/richard-evans/vampire-workshop/blob/master/input-files/1_intro/1d_visualisation/rocksalt.mat

Kind Regards,

Gavin

VAMPIRE user

[lei qiao]

Dear Gavin

Not sure why my reply didn't show up, anyway, thanks a lot for pointing that out, when I changed the numbers under the mat_id, all the data was perfect.

Best wishes,

Lei Qiao

[lei qiao]

Dear Gavin,

Are there any output tags for outputting specific heat in Curie temperature Monte-Carlo simulation? I did not find it in PDF type manual.

Thanks.

Lei Qiao

在2022年10月23日星期日 UTC+2 01:01:38<gabo...@gmail.com> 写道：

[gabo...@gmail.com]

By specific heat, if you are referring to that given by Cv = (<E^2> - <E>^2)/(k_B*T^2) like in the post at [1] or equation (3.14) on page 61 of the University of York dissertation titled "Atomistic simulations of iron oxides" by D. Meilak [2].

It looks like there is an output command, which is output:mean-specific-heat,  that can be put in the input file that is now available in VAMPIRE 6.0.

The VAMPIRE developers may have a better way of creating the pdf manual from their tex files, but in the manual folder for the VAMPIRE version 6.0 source code [3], I ran the following terminal command on my Ubuntu 22.04.1 LTS computer:

username@computername:~/vampire/manual$ xelatex vampire-manual.tex

Even though some error/warning messages were encountered during compiling of the XeTeX [4] using xelatex, it still created a vampire-manual.pdf file.

Attached is a snippet from the vampire-manual.pdf on the output:mean-specific-heat:

[1] https://groups.google.com/g/vampire-users/c/W-98FRlaof4/m/9KUxt6WZGAAJ

[2] https://etheses.whiterose.ac.uk/29771/

[3] https://github.com/richard-evans/vampire/tree/v6.0/manual

[4] https://en.wikipedia.org/wiki/XeTeX

Kind Regards,

Gavin

VAMPIRE user

[lei qiao]

OK, I will try this way to get a new manual. Thanks very much.