Magnetism in Solids and Compounds
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.
Examples of those structures and calculations with Pictures
Ao.Univ.Prof. i.R. Dipl.-Ing. Dr. techn Peter Blaha