This file provides the information about
structure and the magnetic exchange interactions.
For every atom in the crystallographic basis there
has to be given the coordinates, the number of neighbours to be considered, the
Landé factor , the single ion property filename and a set of exchange parameters.
If the exchange parameters (and neighbour positions) are not known for your system, you
can use the program module makenn (see section 18) to generate
a list of nearest neighbours and
exchange parameters, currently implemented in makenn are dipolar interactions,
exchange interactions via the Bethe-Slater curve or the RKKY model. Note that in order
to use makenn you have to set up a working mcphas.j file, which may or
may not contain neighbours and interactions.
mcphas.j - lattice and exchange parameters
Use program addj to add exchange parameter set stored in different
such .j files (see section 18).
- Line 1,2:
- Comment Lines
- Line 3:
- lattice constants a,b,c and crystal angles alpha, beta, gamma
- Line 4-6:
- primitive lattice vectors
- Line 7:
- Number of atoms in the primitive crystallographic unit cell (nofatoms)
- Line 8:
- a comment line with stars
- Line 9:
- coordinates (,,) of 1 magnetic ion in the crystallographic unit cell with
respect to the lattice vectors ,,. The number of neighbours of this
ion, for which interaction constants are given in the interaction table (nofneighbours).
is set to 0 the 9 components of the exchange tensor are given in column 4-12.
is 1, only 3 components are given (column 4-6).
is 2, specific components of the exchange tensor can be given in columns 4 onwards. The indices of these components
must be given in the following line (Line 9a below).
The file name of the corresponding single ion
parameter file (sipffilename).
- Line 9a:
- If diagonalexchange=2, then this line gives the indices of the exchange tensor corresponding to
the columns 4 onwards. It must have a variable called indexexchange followed by a list of names of components of the interaction
tensor separated by space. E.g.
#! indexexchange= JaJb JbJc
means column 4 gives the the interaction constant between the
first angular momentum component of the current ion with the second angular momentum component of its neighbour, whilst
column 5 has the interaction constant between the second angular momentum component of this ion with the third component of its
neighbour. Alternatively, pairs of numbers may be given, as in
#! indexexchange= 1,2 2,3
Additionally another parameter symmetricexchange can be set to 1, where the value in each column is also used
for the transposed tensor component. Thus
#! symmetricexchange=1 indexexchange= JaJb is the same as
#! indexexchange= JaJb JbJa where the 4th and 5th column are the same.
- Line 10:
- Comment line
- Line 11-(10+nofneighbours):
- Interaction table for ion number 1.
Note: the neighbour coordinates (column 1-3) are given with respect to the lattice vectors
,,. The program then calculates from these values the coordinates
with respect to the primitive lattice , , .
Column 4,5,6 ...contain the components of the interaction tensor
Note that in case of non-orthogonal axes the
components of the moments and the interaction tensor
refer to the orthogonal coordinate system
defined with respect to the nonorthogonal lattice
and perpendicular to and .
- Line (11+nofneighbours) - end:
- for each ion in the unit cell line 8 - (10+nofneighbours)
Information for experienced users:
- format of exchange parameter file, which only needs a reduced set of exchange
parameters in the input file. Using the program jjj2j the file can be transformed
to mcphas.j by adding lines for all the equivalent neighbours. The format definition
of mcphas.jjj is the same as mcphas.j, however each line denotes several
equivalent neighbour atoms (instead of only one in mcphas.j) according to the
- If a nonzero coordinate (or ,) in the interaction table
corresponds to it's value at the nearest
lattice point of the primitive lattice,
additional interactions of the same size
with neighbours with coordinate (or ,, respectively)
are taken into account. This
holds for each of the three coordinates , and
resulting in a maximum
number of 8 equivalent neighbours per line in the interaction table.
- If the value of (or ,) is zero or differs
from it's value at the nearest lattice point of the primitive lattice, it is
changed to the value at the nearest lattice point and no interaction
with neighbours with coordinates (or ,) is
taken into account. If such
interaction is needed it may be given in a different line and may
have different magnitude. In this way also crystallographic lattices
with no mirror symmetry may be described.
- exchange parameters etc [ in old format]...see examples for details, use coq2jjj to
transform mcphas.coq to mcphas.jjj format