tgwoodcock / convmag

Conversion between units used in magnetism

convmag

Conversion between various units used in magnetism

The conversions between base units available are:

         T  <->  G         :    1e4
         T  <->  Oe        :    1e4
       A/m  <->  T         :    MU_0
       A/m  <->  G         :    1e4 * MU_0
         G  <->  Oe        :    1
       A/m  <->  Oe        :    1e4 * MU_0
  emu/cm^3  <->  T         :    1e3 * MU_0
erg/Oecm^3  <->  A/m       :    1e3
     emu/g  <->  Am^2/kg   :    1
     J/m^3  <->  GOe       :    1e8 * MU_0
     J/m^3  <->  erg/cm^3  :    1e1
  erg/cm^3  <->  GOe       :    1e7 * MU_0
      Am^2  <->  emu       :    1e3
      Am^2  <->  erg/G     :    1e3
      Am^2  <->  erg/Oe    :    1e3
       emu  <->  erg/G     :    1
       muB  <->  Am^2      :    MU_B
       muB  <->  emu       :    1e3 * MU_B
    muB/fu  <->  T         :    requires user input of lattice parameters

(the factors given above are for the forward conversion)

• permeability of free space, MU_0 = 4 * 3.14159 * 1e-7 H/m (== Vs/Am)

• Bohr magneton, MU_B = 9.274015e-24 Am^2 (muB is the unit string for conversions with Bohr magnetons)

The prefactors available for any base unit are: M (1e6), k (1e3), m (1e-3), µ (1e-6)

You can combine prefactors and base units to give e.g. MA/m or kJ/m^3

A word about emu

emu is not a unit but indicates the system of cgs units being used (emu == electromagnetic units)

The magnetisation data from magnetometers is very often given in emu, and in these cases emu implies the units erg/G. This is why the equivalence emu = erg/G is given above. Many authors still quote emu/g or emu/cm^3 and therefore, these conversions are listed in the table above. convmag always assumes that emu has the units erg/G.

In some cases emu may take other units, so it's always worth checking this!

Installation:

Pip

You can install the current release with pip:

    pip install convmag

Pure python, no other dependencies.

Requires Python >= 3.6 because f-strings are used

Usage options:

1. a console script is provided and should be located in the Scripts directory of your Python distribution after installation. If you have this directory in your Path (environment variable on Windows) you can start the program by typing "convmag" in the console. In this case only single values can be converted (at one time).

2. the package can be imported into python and then you can pass numpy arrays into the function convert_unit(), making sure to keep the default verbose=False. That way many values can be converted at once. The converted values are returned as a numpy array for further processing.

    >>> import numpy as np
    >>> import convmag as cm
    
    >>> vals_in_T = np.arange(0,130,20)
    
    >>> vals_in_T
    array([  0,  20,  40,  60,  80, 100, 120])
   
    >>> vals_in_Oe = cm.convert_unit(vals_in_T, "T", "Oe", verbose=False)
    
    >>> vals_in_Oe
    array([      0.,  200000.,  400000.,  600000.,  800000., 1000000., 1200000.])

Converting between Bohr Magnetons per formula unit and Tesla (muB/fu <-> T)

This conversion requires user input of:

• the lattice parameters a, b, c and gamma, and

• the number of formula units per unit cell.

Only orthogonal (cubic, tetragonal and orthorhombic) and hexagonal unit cells can be handled and therefore gamma = 90° or 120°.

As an example of the number of formula units per unit cell, Nd2Fe14B is the formula unit, which has 17 atoms, and the unit cell contains 68 atoms, so in this case there are 4 formula units per unit cell.

Calling convmag in the console, the conversion from muB to T looks like this:

    Input: 2.3 muB/fu T

    ***INFO: muB per formula unit <-> T***

    Please enter lattice parameters: a b c in Angstrom
    a b c: 3.0 3.0 4.0

    Limited to orthogonal or hexagonal unit cells:
    Please enter gamma in deg. (90 or 120): 90
    Please enter the number of formula units per unit cell:
    f.u./unit cell: 2

    2.3 muB per f.u. = 1.48913 T (2 f.u./unit cell, cell volume = 3.600e-29 m^3)