def test_compute_skyrmion_number_2d_pbc():
mesh = df.RectangleMesh(df.Point(0, 0), df.Point(100, 100), 40, 40)
Ms = 8.6e5
sim = Simulation(mesh, Ms, pbc='2d', unit_length=1e-9)
sim.set_m(init_skx_down)
sim.add(Exchange(1.3e-11))
sim.add(DMI(D=4e-3))
sim.add(Zeeman((0, 0, 0.45 * Ms)))
sim.do_precession = False
sim.relax(stopping_dmdt=1, dt_limit=1e-9)
#df.plot(sim.m_field.f)
#df.interactive()
print np.max(sim.m_field.as_array())
sky_num = compute_skyrmion_number_2d(sim.m_field.f)
print 'sky_num = %g' % sky_num
assert sky_num < -0.95 and sky_num > -1.0
def run_simulation(do_precession):
Ms = 0.86e6
mesh = df.BoxMesh(df.Point(0, 0, 0), df.Point(30e-9, 30e-9, 100e-9), 6, 6,
20)
sim = Simulation(mesh, Ms)
sim.set_m((1, 0, 1))
sim.do_precession = do_precession
sim.add(Demag())
sim.add(Exchange(13.0e-12))
averages = []
for t in ts:
sim.run_until(t)
averages.append(sim.m_average)
return np.array(averages)
def compute_skyrmion_number_2d_example():
mesh = df.CircleMesh(df.Point(0, 0), 20, 4)
Ms = 3.84e5
mu0 = 4 * np.pi * 1e-7
Hz = 0.2
sim = Simulation(mesh, Ms, unit_length=1e-9, name='sim')
sim.do_precession = False
sim.set_m(init_skx_down)
sim.add(Exchange(8.78e-12))
sim.add(DMI(-1.58e-3))
sim.add(Zeeman((0, 0, Hz / mu0)))
sim.relax(stopping_dmdt=1, dt_limit=1e-9)
#sim.m_field.plot_with_dolfin(interactive=True)
print compute_skyrmion_number_2d(sim.m_field.f)
return (np.sin(k * r) * np.cos(phi), np.sin(k * r) * np.sin(phi),
-np.cos(k * r))
else:
return (0, 0, 1)
sim.set_m(m_init)
# -----------------------------------------------------------------------------
# Exchange Energy
sim.add(Exchange(A))
# DMI
sim.add(DMI(D, dmi_type='bulk'))
# Add the corresponding Zeeman field
sim.add(Zeeman((0, 0, B / mu0)))
# -----------------------------------------------------------------------------
sim.do_precession = False
sim.alpha = 0.9
if os.path.exists('vtks'):
shutil.rmtree('vtks')
os.mkdir('vtks')
sim.save_vtk(filename='vtks/m.pvd'.format(0))
sim.relax()
sim.save_vtk(filename='vtks/m.pvd'.format(1))
sim.save_field('m', 'm_relaxed.npy', overwrite=True)