FMR simulations using sinc in time

[Mateusz Zelent]

Hi Serban,

can you help me to verify my simulations. I would like to calculate dipolar coupled bilayers at low external magnetic field. Can you please check my simulation code to get the correct answer? It seems to me that I am still doing something wrong because the magnetization dynamics is still close to zero. 

from NetSocks import NSClient, Shape

ns = NSClient(); ns.configure(True)

l,w,t = [3000e-9,3000e-9,20e-9]

YIGL = ns.Ferromagnet([3000e-9, 3000e-9, 50e-9], [5e-9, 5e-9, 10e-9],meshname="YIGL")

YIGL.modules(['Zeeman', 'exchange','demag'])

YIGL.pbc('x', 8)

YIGL.pbc('y', 8)

disc_xsize = 1000e-9

disc_ysize = 1000e-9

dims = [(l/2)-(disc_xsize/2), (w/2)-(disc_ysize/2), 60e-9, (l/2)+(disc_xsize/2), (w/2)+(disc_ysize/2), 80e-9]

dims = [0,0, 60e-9, l,w, 80e-9]

print(dims)

DISC = ns.Ferromagnet(dims, [5e-9, 5e-9, 10e-9],meshname="DISC")

ns.delrect(meshname="DISC")

DISC.modules(['Zeeman', 'exchange','demag'])

DISC.pbc('x', 8)

DISC.pbc('y', 8)

ns.shape_disk("DISC", 600e-9,600e-9,l/2,w/2,0,20e-9)  

ns.addmodule('supermesh', 'sdemag')

ns.pbc('supermesh', 'x', 8)

ns.pbc('supermesh', 'y', 8)

ns.multiconvolution(1)

gamma = 2.212761569e5

MsDISC = DISC.param.Ms.setparam()

ADISC = DISC.param.A.setparam()

DISC.param.Ms=810e3

DISC.param.A=20e-12

DISC.param.D=0

# DISC.param.grel = gamma / 2.212761569e5

DISC.param.damping = 0.0001

YIGL.param.Ms=139e3

YIGL.param.D=0

YIGL.param.A=4e-12

# YIGL.param.grel = gamma / 2.212761569e5

YIGL.param.damping = 0.0001

YIGL.setangle([89.001, 0.01])

DISC.setangle([89.001, 0.01])

ns.cuda(1)

## RELAXATION

YIGL.setangle([89.001, 0.01])

DISC.setangle([89.001, 0.01])

ns.cuda(1)

ns.displaydetail(50e-9)

ns.vecrep(DISC, 4)

   

B0 = 0.005 #Tesla

H0 = 795775*B0

azymuth = 180.0001

polar = 271

YIGL.setangle([polar, azymuth])

DISC.setangle([polar, azymuth])

ns.setfield("YIGL",H0, azimuthal=azymuth, polar=polar)

ns.setfield("DISC",H0, azimuthal=azymuth, polar=polar)

ns.setfield("supermesh",H0, azimuthal=azymuth, polar=polar)

ns.setode('LLGStatic', 'SDesc')

ns.Relax(['mxh', 5e-14])

 

### DYNAMICS

import numpy as np

f_cut = 15e9  # Maximum cutoff frequency (Hz)

df = 0.1e9  # Frequency resolution (Hz)

# Calculate sampling time step

t_sampl = 0.5 / (f_cut * 1.25)  # Sampling time step (s)

# Calculate the total number of samples needed to achieve the desired frequency resolution

n_of_samples = int(np.ceil(1 / (df * t_sampl)))

# Total time to simulate; increasing this gives you more frequency points in the transform

total_time = 4e-9

# Frequency array for the FFT

freq = np.fft.fftfreq(n_of_samples, t_sampl)

# Debug information

print(f"Sampling time step (t_sampl): {t_sampl:.2e} s")

print(f"Number of samples (n_of_samples): {n_of_samples}")

print(f"Total simulation time (total_time): {total_time:.2e} s")

print(f"Maximum frequency (freq.max()): {freq.max()/1e9:.2f} GHz")

print(f"Frequency resolution (freq[1]): {freq[1]/1e9:.2f} GHz")

# Simulation parameters for the LLG solver

ns.setode('LLG', 'RK4')

dt=2e-13

ns.setdt(dt)

print(250e-15, t_sampl)

# Field and excitation field strength

ns.setdata('commbuf')

ns.iterupdate(100)

ns.setstage('Hequation',"supermesh")

# Set stage stop and data save intervals

ns.editstagestop(0, 'time', total_time)

ns.editdatasave(0, 'time', t_sampl)

# Define the equation constants

# Excitation field (A/m)

# Define excitation field as a sinc function

phi = 0.00001 * np.pi / 180

theta = 89.99999 * np.pi / 180

B0=0.005 #Tesla

H0 = 795775*B0

He = H0 * 0.01

ns.equationconstants('H0', H0)

ns.equationconstants('theta', theta)

ns.equationconstants('phi', phi)

ns.equationconstants('t0', 2e-9)

ns.equationconstants('He', He)

ns.equationconstants('fc', f_cut)

ns.editstagevalue(0,'H0*sin(theta)*cos(phi), H0*sin(theta)*sin(phi), H0*cos(theta))+ He*sinc(2*PI*fc*(t-t0)')

ns.editstagestop(0, 'time', total_time)

ns.editdatasave(0, 'time', t_sampl)

# print(int(t_sampl/dt))

# ns.editdatasave(0, 'iter', int(t_sampl/dt))

import os

path = 'R:/Boris/v5DP_2e14_0005T/'

try:

    os.makedirs(path)

except OSError as error:

    print(error)    

ns.saveovf2mag(f'{path}fmr_%time%.ovf', bufferCommand = True)

ns.cuda(1)

ns.reset()

ns.Run()

[Mateusz Zelent]

Hi,

I think I've managed to achieve satisfactory results, but could you check if I'm making any significant mistakes, particularly with the supermesh?

Notebook attached.  

[Serban Lepadatu]

Hi,

Looks like there's a mistake in this line (brackets in equation not right).

ns.editstagevalue(0,'H0*sin(theta)*cos(phi), H0*sin(theta)*sin(phi), H0*cos(theta))+ He*sinc(2*PI*fc*(t-t0)')

I would change to:

ns.editstagevalue(0,'H0*sin(theta)*cos(phi), H0*sin(theta)*sin(phi), H0*cos(theta)+ He*sinc(2*PI*fc*(t-t0))')

Also setfield command doesn't take "supermesh" as a parameter. If you want to apply the same field to all meshes simply don't specify the mesh name.

Regards,

Serban