Speaker
Prof.
Julie Staunton
Description
Density functional theory (DFT) is extensively used in ab-initio materials modelling. This can be extended by identifying different time scales amongst the collective electronic degrees of freedom. For example, magnetic excitations, which trigger the loss of magnetic order in a magnet with rising temperature, are described by attaching to all Wigner-Seitz cells in a solid local spin-polarisation axes, whose orientations vary very slowly on the time-scale of cell-to-cell electronic propagation [1]. Averaging over these `local moment' degrees of freedom provides a quantitative description of the type and onset of magnetic order, high temperature paramagnetic phases and indeed magnetic phase diagrams. We illustrate this disordered local moment (DLM) theory of finite temperature magnetism with recent work on CoMnSi metallic metamagnets [2]. For many magnetic materials the standard DFT treatment of electron exchange and correlation is inadequate and better approximations are required. One such improvement, the local-self-interaction correction LSIC [3], captures strong electron correlation effects via its focus on the Breit-Wigner type resonant scattering of d- and f- electrons. Here a brief overview of how this theoretical approach has been incorporated into the DLM theory will be given [4] and results shown for the transition metal oxides Mn0, FeO, Co0 and NiO which have anti-ferromagnetic order at low T. We will show how the DLM-LSIC picture solves the puzzle of the large insulating gap persisting into the paramagnetic state [5].
[1] B.L. Gyorffy et al., J.Phys. F 15,1337, (1985).
[2] J.B. Staunton et al., Phys. Rev. B 87, 060404(R), (2013).
[3] M. Lueders et al.,Phys. Rev. B 71:205109, (2005).
[4] I.D. Hughes et al., Nature, 446, 650-653, (2007).
[5] I. D. Hughes et al., New J. Phys. 10, 063010, (2008).
