def run_simulation():
L = W = 12.5e-9
H = 2.5e-9
sim = Sim(mesh, Ms=8.6e5, unit_length=1e-9)
sim.set_m((1, 0.01, 0.01))
sim.alpha = 0.014
sim.gamma = 221017
H_app_mT = np.array([0.0, 0.0, 10.0])
H_app_SI = H_app_mT / (1000 * mu0)
sim.add(Zeeman(tuple(H_app_SI)))
sim.add(Exchange(1.3e-11))
I = 5e-5 # current in A
J = I / (L * W) # current density in A/m^2
theta = 40.0 * pi / 180
phi = pi / 2 # polarisation direction
p = (sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta))
sim.llg.use_slonczewski(J=J, P=0.4, d=H, p=p)
with open(averages_file, "w") as f:
dt = 10e-12
t_max = 10e-9
for t in np.arange(0, t_max, dt):
sim.run_until(t)
f.write("{} {} {} {}\n".format(t, *sim.m_average))
def run_sim_with_stt():
sim = Sim(mesh, Ms=8.6e5)
sim.set_m((1, 0.01, 0.01))
sim.alpha = 0.014
sim.gamma = 221017
H_app_mT = np.array([0.2, 0.2, 10.0])
H_app_SI = H_app_mT / (1000 * mu0)
sim.add(Zeeman(tuple(H_app_SI)))
sim.add(Exchange(1.3e-11))
sim.add(UniaxialAnisotropy(1e5, (0, 0, 1)))
I = 5e-5 # current in A
J = I / (L * W) # current density in A/m^2
theta = 40.0 * pi / 180
phi = pi / 2 # polarisation direction
p = (sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta))
sim.llg.use_slonczewski(J=J, P=0.4, d=5e-9, p=(0, 1, 0))
with open(averages_with, "w") as f:
dt = 5e-12
t_max = 10e-9
for t in np.arange(0, t_max, dt):
sim.run_until(t)
f.write("{} {} {} {}\n".format(t, *sim.m_average))
def run_simulation(stop_when_mx_eq_zero):
"""
Runs the simulation using field #1 from the problem description.
Stores the average magnetisation components regularly, as well as the
magnetisation when the x-component of the average magnetisation crosses
the value 0 for the first time.
"""
mesh = from_geofile(os.path.join(MODULE_DIR, "bar.geo"))
sim = Simulation(mesh, Ms, name="dynamics", unit_length=1e-9)
sim.alpha = alpha
sim.gamma = gamma
sim.set_m(np.load(m_0_file))
sim.add(Demag())
sim.add(Exchange(A))
"""
Conversion between mu0 * H in mT and H in A/m.
mu0 * H = 1 mT
= 1 * 1e-3 T
= 1 * 1e-3 Vs/m^2
divide by mu0 with mu0 = 4pi * 1e-7 Vs/Am
gives H = 1 / 4pi * 1e4 A/m
with the unit A/m which is indeed what we want.
Consequence:
Just divide the value of mu0 * H in Tesla
by mu0 to get the value of H in A/m.
"""
Hx = -24.6e-3 / mu0
Hy = 4.3e-3 / mu0
Hz = 0
sim.add(Zeeman((Hx, Hy, Hz)))
def check_if_crossed(sim):
mx, _, _ = sim.m_average
if mx <= 0:
print "The x-component of the spatially averaged magnetisation first crossed zero at t = {}.".format(
sim.t)
np.save(m_at_crossing_file, sim.m)
# When this function returns True, it means this event is done
# and doesn't need to be triggered anymore.
# When we return False, it means we want to stop the simulation.
return not stop_when_mx_eq_zero
sim.schedule(check_if_crossed, every=1e-12)
sim.schedule('save_averages', every=10e-12, at_end=True)
sim.schedule('save_vtk', every=10e-12, at_end=True, overwrite=True)
sim.run_until(2.0e-9)
return sim.t
def relax_system(mesh):
sim = Sim(mesh, Ms=8.0e5, unit_length=1e-9)
sim.gamma = 2.211e5
sim.alpha = 1
sim.add(Exchange(A=13e-12))
sim.add(Demag())
sim.set_m(init_m)
sim.relax(stopping_dmdt=0.01)
np.save('m0.npy', sim.m)
df.plot(sim._m)
def with_current(mesh):
sim = Sim(mesh, Ms=8.0e5, unit_length=1e-9, name='stt')
sim.gamma = 2.211e5
sim.alpha = 0.1
sim.set_m(np.load('m0.npy'))
sim.add(Exchange(A=13e-12))
sim.add(Demag())
sim.set_zhangli(init_J, 1.0, 0.05)
sim.schedule('save_ndt', every=5e-11)
#sim.schedule('save_vtk', every=5e-11)
sim.schedule(spin_length, every=5e-11)
sim.run_until(8e-9)
df.plot(sim._m)
def run_sim_without_stt():
sim = Sim(mesh, Ms=8.6e5)
sim.set_m((1, 0.01, 0.01))
sim.alpha = 0.014
sim.gamma = 221017
H_app_mT = np.array([0.2, 0.2, 10.0])
H_app_SI = H_app_mT / (1000 * mu0)
sim.add(Zeeman(tuple(H_app_SI)))
sim.add(Exchange(1.3e-11))
sim.add(UniaxialAnisotropy(1e5, (0, 0, 1)))
with open(averages_without, "w") as f:
dt = 5e-12
t_max = 10e-9
for t in np.arange(0, t_max, dt):
sim.run_until(t)
f.write("{} {} {} {}\n".format(t, *sim.m_average))
def run_simulation():
L = W = 12.5e-9
H = 5e-9
sim = Sim(mesh, Ms=8.6e5, unit_length=1e-9)
sim.set_m((1, 0.01, 0.01))
sim.alpha = 0.014
sim.gamma = 221017
H_app_mT = np.array([0.0, 0.0, 10.0])
H_app_SI = H_app_mT / (1000 * mu0)
sim.add(Zeeman(tuple(H_app_SI)))
sim.add(Exchange(1.3e-11))
with open(averages_file, "w") as f:
dt = 10e-12
t_max = 10e-9
for t in np.arange(0, t_max, dt):
sim.run_until(t)
f.write("{} {} {} {}\n".format(t, *sim.m_average))
def create_initial_s_state():
"""
Creates equilibrium s-state by slowly switching off a saturating field.
"""
mesh = from_geofile(os.path.join(MODULE_DIR, "bar.geo"))
sim = Simulation(mesh, Ms, name="relaxation", unit_length=1e-9)
sim.alpha = 0.5 # good enough for relaxation
sim.gamma = gamma
sim.set_m((1, 1, 1))
sim.add(Demag())
sim.add(Exchange(A))
# Saturating field of Ms in the [1, 1, 1] direction, that gets reduced
# every 10 picoseconds until it vanishes after one nanosecond.
H_initial = Ms * np.array((1, 1, 1)) / sqrt(3)
H_multipliers = list(np.linspace(0, 1))
H = Zeeman(H_initial)
def lower_H(sim):
try:
H_mult = H_multipliers.pop()
print "At t = {} s, lower external field to {} times initial field.".format(
sim.t, H_mult)
H.set_value(H_mult * H_initial)
except IndexError:
sim.remove_interaction(H.name)
print "External field is off."
return True
sim.add(H)
sim.schedule(lower_H, every=10e-12)
sim.run_until(0.5e-9)
sim.relax()
np.save(m_0_file, sim.m)
print "Saved magnetisation to {}.".format(m_0_file)
print "Average magnetisation is ({:.2g}, {:.2g}, {:.2g}).".format(
*sim.m_average)
def run_simulation():
L = W = 12.5e-9
H = 5e-9
mesh = df.BoxMesh(df.Point(0, 0, 0), df.Point(L, W, H), 5, 5, 2)
sim = Sim(mesh, Ms=860e3, name="finmag_validation")
sim.set_m((1, 0.01, 0.01))
sim.alpha = 0.014
sim.gamma = 221017
H_app_mT = np.array([0.2, 0.2, 10.0])
H_app_SI = H_app_mT / (1000 * mu0)
sim.add(Zeeman(tuple(H_app_SI)))
sim.add(Exchange(1.3e-11))
sim.add(UniaxialAnisotropy(-1e5, (0, 0, 1)))
I = 5e-5 # current in A
J = I / (L * W) # current density in A/m^2
theta = 40.0 * pi / 180 # polarisation direction
phi = pi / 2
p = (sin(theta) * cos(phi), sin(theta) * sin(phi), cos(theta))
sim.set_stt(current_density=J, polarisation=0.4, thickness=H, direction=p)
sim.schedule("save_averages", every=5e-12)
sim.run_until(10e-9)
# converts Tesla to A/m (divides by mu0)
H_app_strength = flux_density_to_field_strength(1e-3)
# Spin-Polarised Current
current_density = 100e10 # in A/m^2
polarisation = 0.76
thickness = 2.5e-9 # in m
theta = math.pi
phi = math.pi / 2
direction = (math.sin(theta) * math.cos(phi), math.sin(theta) * math.sin(phi),
math.cos(theta))
# Create Simulation
sim = Simulation(mesh, Ms, unit_length, name='disksim')
sim.alpha = alpha
sim.gamma = gamma
sim.set_m((0.01, 0.01, 1.0))
sim.set_stt(current_density, polarisation, thickness, direction)
sim.add(Demag())
sim.add(Zeeman(H_app_strength * H_app_dir))
sim.add(Exchange(A))
sim.add(CubicAnisotropy(u1, u2, K1))
sim.set_tol(reltol=1e-8, abstol=1e-8) # timestepper tolerances
sim.schedule('save_m', every=10 * ps)
sim.schedule('save_averages', every=100 * ps)
sim.run_until(2000 * ps)
