stable state finding

[Semiconductor Quantum Devices Laboratory]

The temp is 4k . How the system is randomized fully? it should relax to a thermally stable state!

nx:= 384*2
ny:= 256
nz:= 8

SetGridSize(nx,ny,nz)
SetCellSize(1e-9,1e-9,1e-9)

Msat=0.8e6
Aex=10e-12
alpha=0.1

sep:=100e-9
major:=170e-9
minor:=85e-9
d:= sep/2 + major/2 //distance between the center of ellipse and center of simulation

ell:= ellipse(major,minor)
e1:=ell.transl(d,0,0)
e2:=ell.transl(-d,0,0)
geo:=(e1.Add(e2)).Intersect(layers(nz/2 -1,nz/2+1))
SetGeom(geo)


m=uniform(1,0,0)
relax()
save(m)

tableadd(m)
FixDt = 50e-14
Temp = 4
tableautosave(10e-12)
run(50e-9)
save(m)
save(B_demag)

[Josh Lauzier]

Hi,

Using a fixed timestep of 50e-14 is unreasonably large, and will cause the solver to give nonsensical results. If you disable the temperature, you will notice you still get the random noise.

It is not required to use FixDt with temperature anymore, and it is not recommended unless you have a specific reason to do so, to avoid exactly this issue. It's easier (and likely faster, since it can adaptively change throughout the simulation and take larger steps when appropriate) to simply let the adaptive solver pick appropriate time steps for you. Running your script briefly and judging based on what the adaptive solver picks, the appropriate timestep for your system is ~1-1.6e-14 or so.

Best,
Josh L.