Magnetism in Solids and Compounds
General
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
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.
Non-collinear Magnetism
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.
Examples of those structures and calculations with pictures
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