Term parameters#

Every energy terms requires one or more input parameters for its definition. For example, (second order) uniaxial anisotropy energy requires the anisotropy constant \(K\) and the anisotropy axis \(\mathbf{u}\). There are three ways how these parameters can be defined:

1. Constant parameters#

If the energy parameters do not vary in space, they can be defined using constant values.

K = 1e5
u = (0, 0, 1)

2. Parameters defined “per region”#

If different regions have different values of parameters, they can be defined “per region”. Let us say there are two regions: “region1” and “region2”. In “region1”, the anisotropy constant is \(5\times10^{5} \text{J}/\text{m}^{3}\) and the anisotropy axis is \((1, 0, 0)\). On the other hand, in “region2”, these parameters are \(3\times10^{5} \text{J}/\text{m}^{3}\) and \((0, 0, 1)\). These two parameters can then be defined using a dictionary:

K = {"region1": 5e5, "region2": 3e5}
u = {"region1": (1, 0, 0), "region2": (0, 0, 1)}

Certain energy terms also require the parameters to be defined between regions. This can be defined by adding an additional item to the dictionary with colon (:) in the key. For example, an exchange energy parameter can be:

A = {"region1": 1e-12, "region2": 2e-12, "region1:region2": 1e-11}

3. Parameters defined using discretisedfield.Field object#

If it is not possible to define the energy parameter using a dictionary because ot varies in space in a non-trivial manner, a parameter can be defined using a field object. For instance:

import discretisedfield as df

p1 = (0, 0, 0)
p2 = (50e-9, 50e-9, 50e-9)
cell = (2e-9, 2e-9, 2e-9)
mesh = df.Mesh(p1=p1, p2=p2, cell=cell)

K = df.Field(mesh, nvdim=1)
u = df.Field(mesh, nvdim=3)

The values of these two (scalar and vector) fields can be then set using Python functions. For further details, plese refer to discretisedfield documentation.