bilayer

[gabo...@gmail.com]

Hello,

I was trying to design a bilayer of two magnetic materials.  I realize my material parameters may not be entirely realistic or fabricable, but it is step towards a process for engineering my bilayer.  As shown below, I ran simulations for a single layer of material 2 (Fe) and a single layer of material 1 (Ni) have two different coercivities of approximately 1.5 T and 3 T as seen attached plots hplotFe.png and hplotNi.png, respectively.

After that, I ran a bilayer simulation for the hysteresis loops for the two materials.  Checking the individual layers in the bilayer gave plots hplot1.png and hplot2.png which as expected look identical to hplotNi.png and hplotFe.png, respectively.  

However, I was expecting and believe the hysteresis curve should look similar to the attached expected_loop.png but the plot I got is different as seen in hplot.png.  If someone else has encountered the same problem and found a solution, I would be interested in what they had to change in the input and/or .mat file for resolving it.

Single Fe Layer

username@computername:~$ lsb_release -a

No LSB modules are available.
Distributor ID:        Ubuntu
Description:        Ubuntu 20.04.4 LTS
Release:        20.04
Codename:        focal
username@computername:~$ cd Fe
username@computername:~/Fe$ mv input_Fe input
username@computername:~/Fe$ ls -l
total 12
-rw-r--r-- 1 username username  844 Mar 23 22:06 Fe.mat
-rw-rw-r-- 1 username username   68 Mar 23 23:54 hplotFe
-rw-r--r-- 1 username username 1472 Mar 23 23:53 input
username@computername:~/Fe$ vampire-serial
                                                _          
                                               (_)        
                    __   ____ _ _ __ ___  _ __  _ _ __ ___
                    \ \ / / _` | '_ ` _ \| '_ \| | '__/ _ \
                     \ V / (_| | | | | | | |_) | | | |  __/
                      \_/ \__,_|_| |_| |_| .__/|_|_|  \___|
                                         | |              
                                         |_|              

                      Version 6.0.0 Dec 31 2021 01:00:23

             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.

================================================================================
Thu Mar 24 00:00:54 2022
================================================================================
Initialising system variables
Creating system
Generating neighbour list..........done!
Copying system data to optimised data structures.
Using generic/normalised form of exchange interaction with 48 total interactions.
Number of atoms generated: 1024
Starting Simulation with Program Hysteresis-Loop...
Simulation run time [s]: 684.718
Simulation ended gracefully.
username@computername:~/Fe$ gnuplot --persist hplotFe

Single Ni Layer

username@computername:~/Fe$ cd ../Ni
username@computername:~/Ni$ mv input_Ni input
username@computername:~/Ni$ ls -l
total 12
-rw-rw-r-- 1 username username   69 Mar 23 23:55 hplotNi
-rw-r--r-- 1 username username 1472 Mar 23 23:53 input
-rw-r--r-- 1 username username  794 Mar 23 22:26 Ni.mat
username@computername:~/Ni$ vampire-serial
                                                _          
                                               (_)        
                    __   ____ _ _ __ ___  _ __  _ _ __ ___
                    \ \ / / _` | '_ ` _ \| '_ \| | '__/ _ \
                     \ V / (_| | | | | | | |_) | | | |  __/
                      \_/ \__,_|_| |_| |_| .__/|_|_|  \___|
                                         | |              
                                         |_|              

                      Version 6.0.0 Dec 31 2021 01:00:23

             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.

================================================================================
Thu Mar 24 00:20:08 2022
================================================================================
Initialising system variables
Creating system
Generating neighbour list..........done!
Copying system data to optimised data structures.
Using generic/normalised form of exchange interaction with 48 total interactions.
Number of atoms generated: 1024
Starting Simulation with Program Hysteresis-Loop...
Simulation run time [s]: 685.871
Simulation ended gracefully.
username@computername:~/Ni$ gnuplot --persist hplotNi

Bilayer

username@computername:~/Ni$ cd ../bilayer
username@computername:~/bilayer$ mv input_bilayer input
username@computername:~/bilayer$ ls -l
total 20
-rw-r--r-- 1 username username 1220 Mar 23 23:58 bilayer.mat
-rw-rw-r-- 1 username username   77 Mar 23 23:49 hplot
-rw-rw-r-- 1 username username   70 Mar 23 23:50 hplot1
-rw-rw-r-- 1 username username   71 Mar 23 23:50 hplot2
-rw-r--r-- 1 username username 1498 Mar 23 22:36 input
username@computername:~/bilayer$ vampire-serial
                                                _          
                                               (_)        
                    __   ____ _ _ __ ___  _ __  _ _ __ ___
                    \ \ / / _` | '_ ` _ \| '_ \| | '__/ _ \
                     \ V / (_| | | | | | | |_) | | | |  __/
                      \_/ \__,_|_| |_| |_| .__/|_|_|  \___|
                                         | |              
                                         |_|              

                      Version 6.0.0 Dec 31 2021 01:00:23

             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.

================================================================================
Thu Mar 24 00:26:34 2022
================================================================================
Initialising system variables
Creating system
Generating neighbour list..........done!
Copying system data to optimised data structures.
Using generic/normalised form of exchange interaction with 48 total interactions.
Number of atoms generated: 2048
Starting Simulation with Program Hysteresis-Loop...
Simulation run time [s]: 1413.27
Simulation ended gracefully.
username@computername:~/bilayer$ gnuplot --persist hplot1
username@computername:~/bilayer$ gnuplot --persist hplot2
username@computername:~/bilayer$ gnuplot --persist hplot

Thanks,

Gavin

VAMPIRE user

[milton...@gmail.com]

For the plot the Ni layer (hplot1) column 7 is used, and for Fe (hplot2) column 11 is used. These are the x-components of their respective magnetizations, whereas column 6 is used for the bilayer (hplot) which is the magnitude of its magnetization. Maybe column 3 in will give you the expected curve. I usually multiply the x-component with the magnitude but that's in MATLAB and I don't know how to do it in gnuplot.

Hope that works!
/Milton

[gabo...@gmail.com]

Milton,

Thanks for the hint.  As seen in the attached "bilayerhplot.png", the plotted hysteresis loop now looks like what I had expected.

Gavin

VAMPIRE user