.. module:: magnumfe
.. _field_terms:

Field Terms
===========

Effective field terms and extensions to the LLG are represented by the :class:`LLGTerm` class. magnum.fe comes with a number of predefined :class:`LLGTerm` classes that cover a variety of use cases. As shown in the previous section, a list of :class:`FieldTerm` objects is usually passed to an LLG integrator object in order to integrate the LLG under the influence of different effects. Moreover each :class:`LLGTerm` object has methods to compute the corresponding effective field and energy for a given :class:`State` object.

.. code:: python

  # initialize state with uniform magnetization configuration
  state = State(mesh, m = Constant((1.0, 0.0, 0.0)))

  # initialize demagnetization field object
  demag = DemagField()

  # compute field and save to file
  File("h.pvd") << demag.h(state)

  # compute energy and print on screen
  print demag.E(state)

Both, the field method :code:`h` and the energy method :code:`E` can also be used as virtual attribues.

.. code:: python

  state.h_demag = demag.h()
  state.E_demag = demag.E()

Computation of the field can be restricted to a certain region. Usually, the default region for is the 'magnetic' region. This default can be overriden in the initializer in order to solve for the field in another region.

.. code:: python

  exchange = ExchangeField(region = 'ferromagnetic')

Some of the predefined :class:`LLGTerm` classes describe nonlocal fields, e.g. the :class:`DemagField` and the :class:`OerstedField` class. These classes additionally distinguish between a source region and target region.

.. code:: python

  # compute field generate by the free layer in the free layer
  DemagField(region = 'free_layer')

  # compute field generate by the fixed layer in the free layer
  DemagField(source_region = 'fixed_layer', target_region = 'free_layer')

Some :class:`LLGTerm` classes require certain material parameters to be defined, e.g. the exchagne field requires the exchange constant :code:`Aex` and the saturation magnetization :code:`ms`. Please refer to the following reference documentation for detailed information on the individual llg terms.

:class:`LLGTerm`
++++++++++++++++

.. autoclass:: LLGTerm
   :members:

:class:`AFCoupling`
+++++++++++++++++++

.. autoclass:: AFCoupling
   :members:

:class:`CompositeTerm`
++++++++++++++++++++++

.. autoclass:: CompositeTerm
   :members:

:class:`CubicAnisotropyField`
+++++++++++++++++++++++++++++

.. autoclass:: CubicAnisotropyField
   :members:

:class:`DemagField`
++++++++++++++++++++++

.. autoclass:: DemagField
   :members:

:class:`ExchangeField`
++++++++++++++++++++++

.. autoclass:: ExchangeField
   :members:

:class:`ExternalField`
++++++++++++++++++++++

.. autoclass:: ExternalField
   :members:

:class:`InterfaceDMIField`
++++++++++++++++++++++++++

.. autoclass:: InterfaceDMIField
   :members:

:class:`InterlayerExchange`
+++++++++++++++++++++++++++

.. autoclass:: InterlayerExchange
   :members:

:class:`OerstedField`
+++++++++++++++++++++

.. autoclass:: OerstedField
   :members:

:class:`SAFLayer`
+++++++++++++++++++

.. autoclass:: SAFLayer
   :members:

:class:`SpinTorque`
+++++++++++++++++++

.. autoclass:: SpinTorque
   :members:

:class:`SpinTorqueSlonczewski`
++++++++++++++++++++++++++++++

.. autoclass:: SpinTorqueSlonczewski
   :members:

:class:`SpinTorqueZhangLi`
++++++++++++++++++++++++++

.. autoclass:: SpinTorqueZhangLi
   :members:

:class:`UniaxialAnisotropyField`
++++++++++++++++++++++++++++++++

.. autoclass:: UniaxialAnisotropyField
   :members:

.. [Zhang2004] Zhang, S., & Li, Z. (2004). Roles of nonequilibrium conduction electrons on the magnetization dynamics of ferromagnets. Physical Review Letters, 93(12), 127204.