def main():
MODULE_DIR = os.path.dirname(os.path.abspath(__file__))
L = 10
mesh_unit = SI(1e-9, "m") # mesh unit (1 nm)
layers = [(0.0, L)] # the mesh
discretization = 0.1 # discretization
# Initial magnetization
xfactor = float(SI("m") / (L * mesh_unit))
def m0(r):
return [
np.cos(r[0] * np.pi * xfactor),
np.sin(r[0] * np.pi * xfactor), 0
]
mat_Py = nmag.MagMaterial(name="Py", Ms=SI(1, "A/m"))
sim = nmag.Simulation("Hans' configuration", do_demag=False)
mesh_file_name = '1d.nmesh'
mesh_lists = unidmesher.mesh_1d(layers, discretization)
unidmesher.write_mesh(mesh_lists, out=mesh_file_name)
sim.load_mesh(mesh_file_name, [("Py", mat_Py)], unit_length=mesh_unit)
sim.set_m(m0)
np.save(os.path.join(MODULE_DIR, "nmag_hansconf.npy"),
sim.get_subfield("E_exch_Py"))
return (H_func, SI("A/m"))
#--------------------------------------------
## Here we set up the simulation
# Create the simulation object
sim = nmag.Simulation(sim_name, do_demag=False)
# Set the coupling between the two magnetisations
sim.set_local_magnetic_coupling(mat_Fe2, mat_Dy, SI(-2.2337e-4, "N/A^2"))
# Creates the mesh from the layer structure
mesh_file_name = '%s.nmesh' % mesh_name
if not os.path.exists(mesh_file_name) or new_mesh:
print "Creating the mesh"
mesh_lists = unidmesher.mesh_1d(layers, discretization)
unidmesher.write_mesh(mesh_lists, out=mesh_file_name)
# Load the mesh
if os.path.exists(mesh_file_name):
sim.load_mesh(mesh_file_name, mat_allocation, unit_length=SI(1e-9, "m"))
else:
raise StandardError,"Need file %s" % mesh_file
#--------------------------------------------
## Run the simulation to calculate the hysteresis loop
H_funcs = [H_func(H) for H in Hs]
if go_fast:
# Set additional parameters for the time-integration
def setup(self):
nf = self.norm_factor
# Create the material for Fe2 in DyFe2 and YFe2
# A unique material can be used because the iron moment per unit volume
# in DyFe2 and YFe2 are the same.
# NOTE: The demagnetising field acts as a shape anisotropy in the 1D model:
# H_demag = -M_x which can be expressed as an uniaxial anisotropy
# H_demag = (2 K_1 m*u) / (mu0*M_sat)
# where the axis u = (1, 0, 0) and K_1 = -mu0*M_sat^2/2
# NOTE: Strictly this is wrong
demag_Fe2 = \
nmag.uniaxial_anisotropy(axis=[1, 0, 0],
K1=-self.enable_demag*0.5*mu0*self.Ms_Fe2**2)
mat_Fe2 = \
nmag.MagMaterial(name="Fe2",
Ms=self.Ms_Fe2,
exchange_coupling=self.A_Fe2,
anisotropy=demag_Fe2,
llg_normalisationfactor=SI(nf, "1/s"),
llg_damping=SI(self.damping),
llg_polarisation=SI(self.P),
llg_xi=SI(self.xi))
# Create the material
# the sum comes from taking the data from Jurgen's simulations
# where the total moment in DyFe2 is given Ms_DyFe2 = Ms_Dy - Ms_Fe2
cubic_Dy = \
nmag.cubic_anisotropy(axis1=[1, -1, 0],
axis2=[1, 1, 0],
K1=SI(33.853774961e6, "J/m^3"),
K2=SI(-16.1710504363e6, "J/m^3"),
K3=SI(16.3584237059e6, "J/m^3"))
demag_Dy = \
nmag.uniaxial_anisotropy(axis=[1, 0, 0],
K1=-self.enable_demag*0.5*mu0*self.Ms_Dy**2)
mat_Dy = \
nmag.MagMaterial(name="Dy",
Ms=self.Ms_Dy,
exchange_coupling=SI(0.0e-12, "J/m"),
anisotropy=demag_Dy + cubic_Dy,
llg_normalisationfactor=SI(nf, "1/s"),
llg_damping=SI(self.damping),
llg_polarisation=0.0)
#--------------------------------------------
## Here we set up the simulation
# Create the simulation object
sim = nmag.Simulation(self.sim_name, do_demag=False,
adjust_tolerances=False)
# Set the coupling between the two magnetisations
#sim.set_local_magnetic_coupling(mat_Fe2, mat_Dy, SI(-2.2337e-4, "N/A^2"))
sim.set_local_magnetic_coupling(mat_Fe2, mat_Dy, self.A_lc)
x0 = self.width_soft*0.5
x1 = x0 + self.width_hard
layers = [(-x1, -x0), (-x0, x0), (x0, x1)]
mat_allocation = [("DyFe2_up", [mat_Dy, mat_Fe2]),
("YFe2", mat_Fe2),
("DyFe2_down", [mat_Dy, mat_Fe2])]
# Creates the mesh from the layer structure
if not os.path.exists(self.mesh_file_name) or self.new_mesh:
print "Creating the mesh"
mesh_lists = unidmesher.mesh_1d(layers, self.discretization)
unidmesher.write_mesh(mesh_lists, out=self.mesh_file_name)
sim.load_mesh(self.mesh_file_name, mat_allocation, unit_length=SI(1e-9, "m"))
self.sim = sim
return sim
# Create the material
mat_Py = nmag.MagMaterial(name="Py",
Ms=SI(0.86e6, "A/m"),
exchange_coupling=SI(0, "J/m"), # disables exchange?
anisotropy=nmag.uniaxial_anisotropy(
axis=[0, 0, 1], K1=SI(520e3, "J/m^3")),
llg_gamma_G=SI(0.2211e6, "m/A s"),
llg_damping=SI(0.2),
llg_normalisationfactor=SI(0.001e12, "1/s"))
# Create the simulation object
sim = nmag.Simulation("1d", do_demag=False)
# Creates the mesh from the layer structure
mesh_file_name = '1d.nmesh'
mesh_lists = unidmesher.mesh_1d(layers, discretization)
unidmesher.write_mesh(mesh_lists, out=mesh_file_name)
# Load the mesh
sim.load_mesh(mesh_file_name, [("Py", mat_Py)], unit_length=mesh_unit)
# Set the initial magnetisation
sim.set_m(m0)
# Save the anisotropy field once at the beginning of the simulation
# for comparison with finmag
np.savetxt("anis_t0_ref.txt", sim.get_subfield("H_anis_Py"))
np.savetxt("m_t0_ref.txt", sim.get_subfield("m_Py"))
with open("third_node_ref.txt", "w") as fh:
t = t0 = 0
