Hysteresis loop for 2d materials

sira...@gmail.com

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Nov 4, 2022, 11:38:57 PM11/4/22

to Vampire Users

I am trying to calculate the hysteresis loop for 2d material bilayer at 0K.

I have some questions as follows:

1) I already calculated Tc for mono bi tri and four layer systems for 2d materials where it works, but for loop simulation I am not able to get hysteresis loop.

create:crystal-structure=hcp

create:periodic-boundaries-x
create:periodic-boundaries-y

#------------------------------------------
# System Dimensions:
#------------------------------------------
dimensions:unit-cell-size=3.29 !A
dimensions:unit-cell-size=3.29 !A
dimensions:unit-cell-size=13.19 !A

dimensions:system-size-x= 32.9 !A
dimensions:system-size-y= 32.9 !A
dimensions:system-size-z=8.75 !A
#------------------------------------------
# Material Files:
#------------------------------------------
material:file=Co.mat

#------------------------------------------
# Simulation attributes:
#------------------------------------------

#------------------------------------------
# Program and integrator details
#----------------------------------------
sim:time-step=1E-16
sim:maximum-applied-field-strength= 0.2 !T
sim:minimum-applied-field-strength=-0.2 !T
sim:applied-field-strength-increment= 0.01 !T
sim:applied-field-angle-phi = 0.1 # (degrees from z)
sim:temperature=0
sim:equilibration-time-steps=100000
sim:loop-time-steps =100000
sim:program=hysteresis-loop
sim:integrator=llg-heun

#------------------------------------------
# data output
#------------------------------------------
output:real-time
output:temperature
output:applied-field-strength
output:mean-magnetisation-length
output:magnetisation

screen:real-time
screen:temperature
screen:applied-field-strength
screen:mean-magnetisation-length
screen:magnetisation

and material file are as follow

# Material 1
#---------------------------------------------------
material[1]:material-name=V1
material[1]:damping-constant=1.0
material[1]:atomic-spin-moment=1.27 !muB
material[1]:uniaxial-anisotropy-constant= 3.7e-22
material[1]:material-element=V1
material[1]:minimum-height=0.0
material[1]:maximum-height=0.5
material[1]:initial-spin-direction=1,0,0
#---------------------------------------------------
# Material 2
#---------------------------------------------------
material[2]:material-name=V2
material[2]:damping-constant=1.0
material[2]:atomic-spin-moment=1.27 !muB
material[2]:uniaxial-anisotropy-constant= 3.7e-22
material[2]:material-element=V2
material[2]:minimum-height=0.5
material[2]:maximum-height=1.0
material[2]:initial-spin-direction=1,0,0
#---------------------------------------------------

2) can vampire works for 2d materials loop simulation

3) what is mean by field cooling and how to connect with loop calculation. was it useful for hysteresis loop calculation and how????????

i need your suggestion that how can i calculate my loop for 2d material VSe2???

gabo...@gmail.com

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Nov 6, 2022, 4:53:05 PM11/6/22

to Vampire Users

A generic input example file for a hysteresis loop on slide 102 of the pdf at [1] has:

sim:maximum-applied-field-strength = 2.0 !T

In the input file you posted, it looks like you have 0.2. Is that maximum applied field value larger than the coercivity (Hc) of your magnetic materials for forming a hysteresis loop? If you don't have expected Hc value(s) obtained from an experimental measurement or from another theoretical calculation, then you could start out using an excessively large maximum applied field value or perform multiple simulations increasing the maximum applied field value each time in small increments for trying to find a field that will overcome the Hc value(s).

A hysteresis loop is a plot of magnetization (M) and magnetic applied field (H) at a constant temperature. Where, room temperature (~300 K) is typically the constant temperature of interest. That is because VSM (Vibrating Sample Magnetometers) measure M-H loops at room temperature. Though, VSM do have liquid Helium or Nitrogen cooling option as well as heating options for making non-room temperature measurements [2].

As seen in Figure 4 at [3] of the article by A. G. Kolhatkar et al, field cooling is a plot of M and temperature (T) usually at a constant H.

A data point measured at an occurrence in time having the same M, H, and T values could appear in both hysteresis loop and field cooling plots. Thus, relating the two plots.

As described in [3], the field cooling plot can be useful for finding the blocking temperature (T_B). As seen in Figure 5 at [4] of the article by S. A. Majetich et al, the magnetic spin moments above the blocking temperature can become random causing a material to behave as a non-magnet (i.e, having little to no magnetization). Thus, the field cooling plot could help one select whether it would be worthwhile or not to try to simulate and plot a hysteresis loop at a particular temperature.

Of note, I did come across a VAMPIRE field cooling workshop example at [5], but I have not tried running that example calculation.

[1] https://github.com/richard-evans/vampire-workshop/blob/master/pdf-slides/1_intro/Introduction.pdf

[2] http://www.microsense.net/products-vsm-accessories.htm

[3] https://doi.org/10.3390/ijms140815977

[4] https://doi.org/10.1557/mrs.2013.230

[5] https://github.com/richard-evans/vampire-workshop/tree/master/input-files/3_skyrmions_antiferrmoagnets_and_magnetite/3b_skyrmions_in_built_dmi

Kind Regards,

Gavin

VAMPIRE user