How to apply a spin-transfer torque pulse?

[Xue Ma]

Hello everyone,

I'm currently trying to work with applying magnetic and electric fields to a structure, but I'd like to apply a spin transfer torque pulse or a pulsed field that decays over time? Or something similar? Are there any parameters that must be added to the input to enable STT and control the pulse size and duration?

Thanks,

Xue

[gabo...@gmail.com]

In the VAMPIRE article by A. Meo et al [1], the spin-transfer torque field (B_STT) of equation (12) is proportional to the current density (je):

B_STT ∝ je

In the article, there is je = 5 x 10^12 Am^-2. From that, it looks like a constant value is used.  Though, it sounds like you want a variable value je(t) for a current pulse (or a current density as a function of time).  So, as far as I know, a spin polarized current pulse for spin transfer torque hasn't been implemented in the code yet.

The spintorque folder in the develop branch of VAMPIRE [2] seems like it contains the implementation used in that article.  However, there seems to be a lack of documentation for using it.

I've not tried reaching out to the first author of that article on it usage, but maybe they could be reached with the contact information at [3].

VAMPIRE has a magnetic field pulse (sim:program = field-pulse [4]) but its functionality seemed a bit limited.  Due to that, I saw in one case a previous user modifying the source code as seen in the post at [5].

[1] https://dx.doi.org/10.1088/1361-648X/ac9c80

[2] https://github.com/richard-evans/vampire/tree/develop/src/spintorque

[3] https://www-users.york.ac.uk/~am1808/

[4] https://groups.google.com/g/vampire-users/c/3JXYRDkZeRU/m/y0IwABmnBQAJ

[5] https://groups.google.com/g/vampire-users/c/EjqwEhvlaK0/m/_5NSl_OzBgAJ

HTH and kind regards,

Gavin

VAMPIRE user

[Xue Ma]

Thanks for your reply, I will try it.

[Xue Ma]

If I want to apply STT as in [1], what parameters should I add to my input file?


How do I enable STT or SOT? Just set the current density? Which parameter is the direction?

Looking forward to your reply, thank you！

Xue

[gabo...@gmail.com]

If I want to apply STT as in [1], what parameters should I add to my input file?

 

As I've not fully figured out how to use the STT in VAMPIRE, I cannot be of much help with that.  Though, there was a dissertation at [2] that I came across with an input file that might be a good example, but I still have not yet tried it.

How do I enable STT or SOT?

 

For STT, you could try in the input file the command [3]:

spin-torque:enable-ST-fields

For SOT, in the source code [4], you could trying changing the line:

bool enable_spin_torque_fields = false; // flag to enable spin torque fields

to

bool enable_spin_torque_fields = true; // flag to enable spin torque fields

Just set the current density?

 

You could try the following command for example in the input file [3]:

spin-torque:current-density=0.1e12

Which parameter is the direction?

In Dou's input file at [5], I saw a spin torque current set in the x direction with:

spin-torque:current-direction=x

Or you might need [6,7]:

sim:slonczewski-spin-polarization-unit-vector=1,0,0

[1] https://dx.doi.org/10.1088/1361-648X/ac9c80

[2] https://groups.google.com/g/vampire-users/c/xP0hVuJa104/m/6jcmYrmwAwAJ

[3] https://groups.google.com/g/vampire-users/c/xP0hVuJa104/m/O2UgicRIBwAJ

[4] https://groups.google.com/g/vampire-users/c/xT2utJ0KEHc/m/IVGrhZ-uAwAJ

[5] https://groups.google.com/g/vampire-users/c/xP0hVuJa104/m/EFSH4LBgBgAJ

[6] https://groups.google.com/g/vampire-users/c/5eABY8oy97A/m/_PKZjJQJBAAJ

[7] https://groups.google.com/g/vampire-users/c/L9BzL7s-490/m/QPuNcbNWAgAJ

[Xue Ma]

I added the following parameters：spin-torque:enable-ST-fields
spin-torque:current-density=0.1e12
spin-torque:current-direction=1,1,-2, but when I run the task I get an error:

[gabo...@gmail.com]

In the dissertation at [1], there is a page for an input file and pages for a mat file.

The input file should be on page 86:

I typed each line from that into a text file and saved it.  It gave me that attached input file which has spin-torque:enable-ST-fields, spin-torque:current-density, and spin-torque:current-direction like in your email below.

I also did the same with the material file, such that I got the attached spintorquestack.mat.

VAMPIRE ran successfully.  So, there might be other spin torque related lines in the input or material file needed for it to work.  I also found after the simulation that spin torque output files of the microcells had been created such as st-microcells-base.cfg and st-microcells-00000001.cfg as shown below:

username@computername:~/Desktop/spintorque$ ls -l
total 8
-rw-rw-r-- 1 username username  615 Jan 17 15:45 input
-rw-rw-r-- 1 username username 3069 Jan 17 14:52 spintorquestack.mat
username@computername:~/Desktop/spintorque$ ~/vampire/vampire-serial
                                                _          
                                               (_)        
                    __   ____ _ _ __ ___  _ __  _ _ __ ___
                    \ \ / / _` | '_ ` _ \| '_ \| | '__/ _ \
                     \ V / (_| | | | | | | |_) | | | |  __/
                      \_/ \__,_|_| |_| |_| .__/|_|_|  \___|
                                         | |              
                                         |_|              

                      Version 6.0.0 Dec 27 2023 21:07:16

             Git commit: 4c9651daecc86c3e6b6df0c8055fcd9e89fd900c

  Licensed under the GNU Public License(v2). See licence file for details.

  Lead Developer: Richard F L Evans <richar...@york.ac.uk>

  Contributors: Sarah Jenkins, Andrea Meo, Andrew Naden, Matthew Ellis,
                Oscar Arbelaez, Sam Morris, Rory Pond, Weijia Fan,
                Phanwadee Chureemart, Pawel Sobieszczyk, Joe Barker,
                Thomas Ostler, Andreas Biternas, Roy W Chantrell,
                Wu Hong-Ye, Razvan Ababei, Sam Westmoreland,
                Daniel Meilak
 
                Compiled with:  GNU C++ Compiler
                Compiler Flags:

  Vampire includes a copy of the qhull library from C.B. Barber and The
  Geometry Center and may be obtained via http from www.qhull.org.

================================================================================
Fri Jan 17 15:47:46 2025
================================================================================
Initialising system variables
lsdl0 120
lsdl1 120
lsdl2 120
lsdl3 120
Creating system
Generating neighbour list..........done!
Copying system data to optimised data structures.
Using generic/normalised form of exchange interaction with 16 total interactions.
Number of atoms generated: 55142
Starting Simulation with Program Time-Series...
Simulation run time [s]: 26.3003
Simulation ended gracefully.
username@computername:~/Desktop/spintorque$ ls -l *-base.cfg *00000001.cfg
-rw-rw-r-- 1 username username 175891 Jan 17 15:47 st-microcells-00000001.cfg
-rw-rw-r-- 1 username username  77985 Jan 17 15:48 st-microcells-base.cfg

I was able to open any one of the st-mirocells*.cfg files with a text editor.  The first line looks to be labeled as the time.  However, I see no column labels for rows 2 through N.  So, I currently don't know what that data is.

[1] http://202.28.34.124/dspace/handle/123456789/1897

Hope that helps and kind regards,

Gavin

VAMPIRE user