Slonczewski#

class micromagneticmodel.Slonczewski(**kwargs)#

Slonczewski spin transfer torque dynamics term.

\[\frac{\text{d}\mathbf{m}}{\text{d}t} = \gamma\beta\frac{\epsilon + \alpha\epsilon'}{1+\alpha^{2}} \mathbf{m} \times (\mathbf{m}_\text{p} \times \mathbf{m}) -\gamma\beta\frac{\epsilon' - \alpha\epsilon}{1+\alpha^{2}} \mathbf{m} \times \mathbf{m}_\text{p}\]
\[\beta = \left| \frac{\hbar}{\mu_{0}e} \right| \frac{J}{tM_\text{s}}\]
\[\epsilon = \frac{P\Lambda^{2}}{(\Lambda^{2} + 1) + (\Lambda^{2} - 1)(\mathbf{m}\cdot\mathbf{m}_\text{p})}\]

A time-dependent current can be specified by providing a time-dependent pre-factor that is used to multiply J. The time-dependence can either be specified by providing a callable func that is evaluated at time steps dt or by passing a dictionary tcl_strings of tcl strings that are written to the mif file.

Parameters:

  • J (numbers.Real, dict, discretisedfield.Field) – If a single value numbers.Real is passed, a spatially constant parameter is defined. For a spatially varying parameter, either a dictionary, e.g. J={'region1': 5e12, 'region2': 3e12} (if the parameter is defined “per region”) or discretisedfield.Field is passed.

  • mp ((3,) array_like, dict, discretisedfield.Field) – If a single vector value is passed, a spatially constant parameter is defined. For a spatially varying parameter, either a dictionary, e.g. mp={'region1': (0, 0, 1), 'region2': (0, 1, 0)} (if the parameter is defined “per region”) or discretisedfield.Field is passed.

  • P (numbers.Real, dict, discretisedfield.Field) – If a single positive value numbers.Real is passed, a spatially constant parameter is defined. For a spatially varying parameter, either a dictionary, e.g. P={'region1': 0.4, 'region2': 0.35} (if the parameter is defined “per region”) or discretisedfield.Field is passed.

  • Lambda (numbers.Real, dict, discretisedfield.Field) – If a single positive value numbers.Real is passed, a spatially constant parameter is defined. For a spatially varying parameter, either a dictionary, e.g. Lambda={'region1': 1.5, 'region2': 2} (if the parameter is defined “per region”) or discretisedfield.Field is passed.

  • eps_prime (numbers.Real, dict, discretisedfield.Field) – If a single value numbers.Real is passed, a spatially constant parameter is defined. For a spatially varying parameter, either a dictionary, e.g. eps_prime={'region1': 0.4, 'region2': 0.35} (if the parameter is defined “per region”) or discretisedfield.Field is passed. Defaults to 0.

  • func (callable, optional) – Callable to define arbitrary time-dependence, multiplies J. Called at times that are multiples of dt. Must return a single number.

  • dt (numbers.Real, optional (required for func)) – Time steps in seconds to evaluate callable func at.

  • tcl_strings (dict, optional) – Dictionary of tcl strings to be included into the mif file for more control over specific time-dependencies. Must contain the following keys: script, script_args, and script_name. Refer to the OOMMF documentation for more details ( https://math.nist.gov/oommf/doc/userguide20a3/userguide/Standard_Oxs_Ext_Child_Clas.html#SX).

Examples

  1. Defining spatially constant Slonczewski dynamics term.

>>> import micromagneticmodel as mm
...
>>> slonczewski = mm.Slonczewski(J=7.5e12, mp=(1, 0, 0), P=0.4, Lambda=2)

  1. Defining spatially varying Slonczewski dynamics term.

>>> import discretisedfield as df
...
>>> region = df.Region(p1=(0, 0, 0), p2=(5e-9, 5e-9, 5e-9))
>>> mesh = df.Mesh(region=region, n=(5, 5, 5))
>>> J = df.Field(mesh, nvdim=1, value=1e12)
>>> slonczewski = mm.Slonczewski(J=J, mp=(1, 0, 0), P=0.4, Lambda=2,
...                              eps_prime=2)

  1. Defining an exponentially decaying current.

>>> import micromagneticmodel as mm
...
>>> def decay(t):
...     t_0 = 1e-10
...     return np.exp(-t / t_0)
>>> slonczewski = mm.Slonczewski(J=7.5e12, mp=(1, 0, 0), P=0.4, Lambda=2,
...                              func=decay, dt=1e-13)

  1. An attempt to define the Slonczewski dynamics term using a wrong value (here using a scalar for mp where a vector is required).

>>> # scalar value for mp
>>> slonczewski = mm.Slonczewski(J=J, mp=5, P=0.4, Lambda=2)
Traceback (most recent call last):
...
TypeError: ...

Methods

__add__

Binary + operator.

__dir__

Default dir() implementation.

__eq__

Relational operator ==.

__iter__

Iterator.

__repr__

Representation string.

dmdt

Properties

J

Descriptor allowing setting attributes with a value described as descriptor or a dictionary.

Lambda

Descriptor allowing setting attributes with a value described as descriptor or a dictionary.

P

Descriptor allowing setting attributes with a value described as descriptor or a dictionary.

dt

Descriptor allowing setting attributes only with scalars (numbers.Real).

eps_prime

Descriptor allowing setting attributes with a value described as descriptor or a dictionary.

func

Descriptor allowing setting attributes only with values of a certain type.

mp

Descriptor allowing setting attributes with a value described as descriptor or a dictionary.

name

Name.

tcl_strings

Descriptor allowing setting attributes with a dictionary, which has keys defined by key_descriptor and values defined by value_descriptor.