#!/usr/bin/env python
# coding: utf-8

# # Time-varying field
# 
# In this tutorial, we introduce how a time-dependent external magnetic field can be defined in energy equation. We start by importing the modules we are going to use:

# In[1]:


import oommfc as mc
import discretisedfield as df
import micromagneticmodel as mm


# For the sample, we choose a one-dimensional chain of magnetic moments.

# In[2]:


p1 = (-10e-9, 0, 0)
p2 = (10e-9, 1e-9, 1e-9)
cell = (1e-9, 1e-9, 1e-9)
region = df.Region(p1=p1, p2=p2)
mesh = df.Mesh(region=region, cell=cell)


# The mesh is:

# In[3]:


mesh.mpl(box_aspect=(10, 3, 3))


# Now, we can define the system object and add a time-dependent sine-wave field to our energy equation. We need to pass:
# 
# - Field `H` which is multiplied by time-dependent function at each time step,
# - wave shape `func='sin'`
# - frequency `f`, and
# - time shift `t0`.
# 
# Accordingly, the time-dependent Zeeman field is then:
# 
# $$\mathbf{H}(t) = \mathbf{H}_\text{amp}\sin(2\pi f (t-t_{0}))$$

# In[4]:


system = mm.System(name="time_dependent_field")

system.energy = mm.Exchange(A=1.6e-11) + mm.Zeeman(
    H=(1e6, 2e6, 3e6), func="sin", f=1e9, t0=1e-9
)
system.dynamics = mm.Precession(gamma0=mm.consts.gamma0) + mm.Damping(alpha=1e-5)

system.m = df.Field(mesh, nvdim=3, value=(0, 0, 1), norm=1.1e6)


# Now, we can run the simulation using `TimeDriver`:

# In[5]:


td = mc.TimeDriver()
td.drive(system, t=5e-9, n=200)


# In the system table, there are columns with field values:

# In[6]:


system.table.data


# In[7]:


system.table.mpl(y=["Bx_zeeman", "By_zeeman", "Bz_zeeman"])


# Similarly, we can define a cardinal sine wave ("sinc pulse"). We need to pass:
# 
# - Field `H` which is multiplied by time-dependent function at each time step,
# - wave shape `wave='sinc'`
# - cut-off frequency `f`, and
# - time shift `t0`.
# 
# Accordingly, the time-dependent Zeeman field is then:
# 
# $$\mathbf{H}(t) = \mathbf{H}_\text{amp}\text{sinc}(2\pi f_{c} (t-t_{0})) = \mathbf{H}_\text{amp}\frac{\text{sinc}(2\pi f_{c} (t-t_{0}))}{2\pi f_{c} (t-t_{0})}$$

# In[8]:


system = mm.System(name="time_dependent_field")

system.energy = mm.Exchange(A=1.6e-11) + mm.Zeeman(
    H=(1e6, 2e6, 3e6), func="sinc", f=1e9, t0=5e-9
)
system.dynamics = mm.Precession(gamma0=mm.consts.gamma0) + mm.Damping(alpha=1e-5)

system.m = df.Field(mesh, nvdim=3, value=(0, 0, 1), norm=1.1e6)

td = mc.TimeDriver()
td.drive(system, t=10e-9, n=200)

system.table.mpl(y=["Bx_zeeman", "By_zeeman", "Bz_zeeman"])