spinw.addcoupling method

assigns an exchange matrix to a bond

Syntax

addcoupling(obj,Name,Value)

Description

addcoupling(obj,Name,Value) assigns a matrix (will be used as exchange matrix) to a given bond after bonds are generated using spinw.gencoupling.

Examples

To add the $J_1$ diagonal matrix to all second neighbor bonds between magnetic atoms use the following:

cryst = sw_model('squareAF',1)
cryst.addmatrix('label','J1','value',diag([1 0.1 0.1]))
cryst.gencoupling
cryst.addcoupling('mat','J1','bond',2)
plot(cryst,'range',[2 2 1])

Input Arguments

obj: spinw object.

Name-Value Pair Arguments

'mat'

Label (string) or index (integer) of the matrix that will be assigned to selected bonds, e.g. 'J1'.

'bond'

Integer that selects bonds, e.g. 1 for first neighbor, 2 for second neighbor, etc. The given value is compared to the obj.coupling.idx vector and the exchange matrix will be assigned to matching bonds. 'bond' can be also a row vector to assign matrices to multiple bonds.

'atom'

Contains labels of atoms (string) or index of atoms (integer) that is compared to spinw.unit_cell where all symmetry inequivalent atoms are stored. If a single string label or number is given, e.g. 'Cr1' only Cr1-Cr1 bonds will be assigned. If a cell with 2 strings, e.g.

{'Cr1'
'Cr2'}

only Cr1-Cr2 bonds will be assigned. Default value is [].

'subIdx'

If the above options are not enough to select the desired bonds, using subIdx bonds can be selected one-by-one from the list of bonds that fulfill the constraint of atom and bond.

'type'

Type of the coupling with possible values of:

'quadratic' Quadratic exchange, default.
'biquadratic' Biquadratic exchange.

'sym'

If true, symmetry operators will be applied on the exchange matrices to generate the coupling on symmetry equivalent bonds, if false all symmetry equivalent bonds will have the same exhcange matrix.

Warning: Setting atom or subIdx parameters will remove the symmetry operations on the selected bonds. This means that assigning any non-Heisenberg exchange matrix will break the space group defined in obj.lattice.sym. Effectively reducing the symmetry of the given bond to P0

Output Arguments

The function adds extra entries to the spinw.coupling property of obj. Specifically it will modify obj.coupling.mat_idx, obj.coupling.type and obj.coupling.sym matrices.