To estimating spin polarization efficiency

[jmiasif]

Dear ubermag team @fangohr @marijanbeg
1st Calculate Spin Current Density Js then Calculate Charge Current Density Jc
after this spin polarisation eficiency = Js/Jc
∂m/∂t=−γ 0m×Heff+αm× ∂m/∂t+Ts
Js =− (γ0/μ0Ms)m×Heff
Jc=V/R

import oommfc as oc
import discretisedfield as df
import micromagneticmodel as mm
# 1. Set up the thin film geometry
Lx = Ly = 100e-9  # Film dimensions in the x and y directions (m)
thickness = 5e-9  # Film thickness (m)
cell_size = (5e-9, 5e-9, 5e-9)  # Cell size (m)

mesh = df.Mesh(p1=(0, 0, 0), p2=(Lx, Ly, thickness), cell=cell_size)

# 2. Define the Hamiltonian
A = 1e-11  # Exchange constant (J/m)
K = 1e3  # Anisotropy constant (J/m^3)
Ms = 1.32e6  # Saturation magnetization (A/m)
H = (0, 0, 1e6)  # External magnetic field (A/m)
exchange = mm.Exchange(A=A)
anisotropy = mm.UniaxialAnisotropy(K=K, u=(0, 0, 1))
zeeman = mm.Zeeman(H=H)
hamiltonian = exchange + anisotropy + zeeman
system = mm.System(name="thin_film")
system.hamiltonian = hamiltonian

# 3. Specify the dynamics
alpha = 0.1  # Gilbert damping parameter
gamma0 = 2.211e5
system.dynamics = mm.Precession(gamma0=gamma0) + mm.Damping(alpha=alpha)

# 4. Set up the initial magnetization configuration
def m_initial(pos):
    x, y, z = pos
    if z < thickness / 2:
        return (1, 0, 0)  # Magnetization pointing in the x-direction
    else:
        return (-1, 0, 0)  # Magnetization pointing in the opposite x-direction

system.m = df.Field(mesh, nvdim=3, value=m_initial, norm=Ms)

# 5. Run the simulation
td = oc.TimeDriver()
td.drive(system, t=1e-9, n=100)
# 7. Calculate Spin and Charge Current Densities
mu0 = 4 * np.pi * 1e-7  # Permeability of free space (H/m)

# Calculate effective field
Heff = system.hamiltonian.effective_field(system.m)

# Calculate spin current density
Js = -gamma0 / (mu0 * Ms) * df.Field(mesh, value=np.cross(system.m.array, Heff))

# Calculate charge current density if applicable
# Replace the following with actual values from your simulation
V = 1  # Applied voltage (V)
R = 1  # Resistance of the device (Ohm)
Jc = V / R

print("Spin current density:", Js)
print("Charge current density:", Jc)

​but it give error

`AxisError Traceback (most recent call last)
Cell In[18], line 8
5 Heff = system.hamiltonian.effective_field(system.m)
7 # Calculate spin current density
----> 8 Js = -gamma0 / (mu0 * Ms) * df.Field(mesh, value=np.cross(system.m.array, Heff))
10 # Calculate charge current density if applicable
11 # Replace the following with actual values from your simulation
12 V = 1 # Applied voltage (V)

File ~\miniconda3\envs\ubermag\Lib\site-packages\numpy\core\numeric.py:1588, in cross(a, b, axisa, axisb, axisc, axis)
1586 # Check axisa and axisb are within bounds
1587 axisa = normalize_axis_index(axisa, a.ndim, msg_prefix='axisa')
-> 1588 axisb = normalize_axis_index(axisb, b.ndim, msg_prefix='axisb')
1590 # Move working axis to the end of the shape
1591 a = moveaxis(a, axisa, -1)

AxisError: axisb: axis -1 is out of bounds for array of dimension 0`

please help me out i want to calculate value of Jc and Js as well as graph of it from where we can find the value of these Js and Jc.

​

[lang-m]

Hi @jmiasif , could you please report what get when you use Heff = system.energy.effective_field(system.m).

[jmiasif]

Hi Sir @lang-m

Running OOMMF (ExeOOMMFRunner)[2024/05/17 15:17]... (13.8 s)
Effective field (Heff) is None. Unable to calculate spin current density.
Effective field (Heff): None
Shape of system.m.array: (20, 20, 1, 3)
i hope this result you are asking. if anything else is needed please ask.

thank you so much