Using spin-polarized band structure calculations the magnetic properties of ferro-, antiferro- and ferrimagnetic materials are studied by the Linearized Augmented Plane Wave (LAPW) method. The Fixed Spin Moment (FSM) method (K.Schwarz and P.Mohn, J.Phys.F: Metal Phys, 14, L129, 1984)- originally implemented into the Augmented Spherical Wave (ASW) scheme - can be used in cases where the total energy as a function of the magnetic moment is needed for further analysis.
INVAR alloys (e.g. Fe65Ni35) have an almost vanishing thermal expansion coefficient in a certain temperature range. This behaviour is due to a strong magneto-volume coupling and can be explained on the basis of itinerant spin fluctuations.
While for many magnetic materials the magnetic moments at all atoms point in
the same direction (or have a simple antiferromagnetic up-dn alignment)
there are other materials where the direction of moments varies from atom to
atom. This is called
non-collinear order of the magnetic momenta.
In order to calculate properties of such systems we have to extend
our LAPW code (WIEN2k). The implementation of
non-collinear magnetism utilises a rotated spinors
basis set inside atomic spheres, and pure-spinors basis
inside the interstitial. This allows calculations in both, the
atomic-moment-approximation as well as in full non-collinear
mode, and inclusion of spin-orbit coupling (for heavier elements) as well as
LDA+U corrections (for "correlated" systems) are also possible.
In the atomic-moment-approximation only the
diagonal part of the spin-potential and the density matrixes
inside the atomic spheres are taken into account, but
in the interstitial region the full potential and density
matrix is used. Often this is a very reasonable approximation since
non-collinearity within an atom is small, but from on atom to the next the
magnetisation rotates and this is taken into account properly.
In the full mode also
off-diagonal terms inside the spheres are considered and highest precission
of the calculation is reached.
