richard....@gmail.com

[Sucheta Mondal]

Dear Richard,
Can I get your help in sorting out some basic problems in vampire ?
I have just started to simulate hysteresis loop using Vampire but the coercivity of the system is coming to be very high for any temperature. Though I am keeping the bias field interval between each point in the order of Oe or kOe, the coercivity is coming out to be in Tesla order.
Here is the example of the input file . Your suggestion will be very helpful...
#------------------------------------------
# Sample vampire input file to perform
# hysteresis calculation for v4.0
#
#------------------------------------------

#------------------------------------------
# Creation attributes:
#------------------------------------------
create:crystal-structure=sc

#------------------------------------------
# System Dimensions:
#------------------------------------------
dimensions:unit-cell-size = 3.54 !A
dimensions:system-size-x = 7.7 !nm
dimensions:system-size-y = 7.7 !nm
dimensions:system-size-z = 7.7 !nm

#------------------------------------------
# Material Files:
#------------------------------------------
material:file=Co.mat

#------------------------------------------
# Simulation attributes:
#------------------------------------------
sim:temperature=300
sim:equilibration-time-steps=10000
sim:loop-time-steps=10000
sim:maximum-applied-field-strength=10
sim:minimum-applied-field-strength=-10
sim:applied-field-strength-increment=0.1
sim:applied-field-unit-vector=0.00001,0,0.99999

#------------------------------------------
# Program and integrator details
#------------------------------------------
sim:program=hysteresis-loop
sim:integrator=llg-heun

#------------------------------------------
# data output
#------------------------------------------
output:applied-field-strength
output:magnetisation
output:output-rate = 1000


screen:applied-field-strength
screen:magnetisation

config:atoms
config:atoms-output-rate=10

[Jung-Wei Liao]

Hi

Can you also show us your material input file (.mat)?

Best

Jung-Wei

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[Muftah Al-Mahdawi]

Dear Sucheta,

It seems similar to the mistake I did before.
llg-heun integrator needs longer integration time and a smaller time-step. So very short ones, like what you have (you set time-step to default), can give the impression of increased coercivity.
For example, these worked for me to simulate Co near Tc:
sim:time-steps-increment=2
sim:equilibration-time-steps=1000000
sim:loop-time-steps=1000000
sim:time-step=1.0E-17

For lower temperatures, I think a time-step of 1e-16 and equilibration steps of order of 100k might work. A trial is needed.

Regards,
Miftah

-- 
=============================================================
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Crossing-Correlation Spin Electronics Lab (Sahashi group).
Dept. of Electronic Engineering, Tohoku University.

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