bcc_Fe_dlm
Full name: ase2sprkkr.examples.A10_DLM.bcc_Fe_dlm
Description
Script demonstrating how to set up a disordered local moment (DLM) calculation using bcc Fe as the test case.
Such calculations are used to describe the paramagnetic state of materials, where local magnetic moments on atoms persist, but where the net magnetisation of the material is zero on account of thermally induced spin fluctuations. The CPA is used to average over possible orientations of magnetic moment. Above the Curie temperature, all orientations of magnetic moment are equally probably, and the probability distribution of orientations of magnetic moments is uniform on the sphere. In the absence of spin-orbit coupling, the CPA condition for a full average (using an angular integral) over the sphere with uniform probability distribution can be shown to be mathematically equivalent to the CPA condition for a 50:50 Ising ‘alloy’ of ‘up’ and ‘down’ magnetic moments. (Note that this equality does not strictly hold in the case where spin-orbit effects are present, as in a fully relativistic calculation.)
A DLM calculation should be iterated to self-consistency to check whether the local moments ‘collapse’ (as frequently happens for elements like Cr, Ni) or whether they are self-sustaining (as is typical for Fe, Co).
Once you have run this script and iterated to self-consistency, if you run tail Fe.pot_new you should find that, although the net magnetisation of the calculation is zero, the two Fe atoms have equal and opposite magnetic moments, each of magnitude approximately 2.16 mu_B. This confirms that the local moments are self-sustaining, and that bcc Fe is a ‘good’ local moment system.
- Some appropriate references for the disordered local moment (DLM) picture are:
Pindor et al., J. Phys. F: Met. Phys. 13, 979 (1983)
Staunton et al., J. Magn. Magn. Mater. 45, 15-22 (1984)
Gyorffy et al., J. Phys. F: Met. Phys. 15, 1337 (1985)
Author: Christopher D. Woodgate, University of Bristol, 2025
Email: christopher.woodgate@bristol.ac.uk
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