Complex magnetic representation
If the expectation value of the spin operator is non-zero () the spin vectors will make a pattern that can be mathematically best described by its Fourier transform. A concise description of this topic can be found in the article A. Wills: Magnetic structures and their determination using group theory.
To define a magnetic structure first we need to find the correct magnetic unit cell. Although in magnetic structure determination most often the magnetic and the crystallographic unit cells are identical, in SpinW it is possible to define a magnetic supercell, that is the multiples of the crystallographic unit cell. This can help sometimes to optimize the spin wave calculation and gives more flexibility to test new models without changing the crystal structure. The magnetic structure is stored in the spinw.mag_str property of the SpinW class with the nExt subfield (int32 type) storing the size of the magnetic supercell in units of the crystallographic unit cell. By default the magnetic supercell is identical to the crystallographic one which is given by nExt=[1 1 1].
Once we defined the magnetic unit cell, the