Magnetic Compton scattering, x-ray magnetic circular dichroism spectroscopy, and bulk magnetometry measurements are performed on a set of medium-(NiFeCo and NiFeCoCr) and high-entropy (NiFeCoCrPd and NiFeCoCrMn) Cantor-Wu alloys. The bulk spin momentum densities determined by magnetic Compton scattering are remarkably isotropic, and this is a consequence of the smearing of the electronic structure by disorder scattering of the electron quasiparticles. Nonzero x-ray magnetic circular dichroism signals are observed for every element in every alloy indicating differences in the populations of the majority and minority spin states implying finite magnetic moments. When Cr is included in the solid solution, the Cr spin moment is unambiguously antiparallel to the total magnetic moment, while a vanishingly small magnetic moment is observed for Mn, despite calculations indicating a large moment. Some significant discrepancies are observed between the experimental bulk and surface magnetic moments. Despite the lack of quantitative agreement, the element-specific surface magnetic moments seem to be qualitatively reasonable.

Many-body theories such as dynamical mean field theory (DMFT) have enabled the description of the electron-electron correlation effects that are missing in current density functional theory (DFT) calculations. However, there has been relatively little focus on the wave functions from these theories. We present the methodology of the newly developed ELK-TRIQS interface and how to calculate the DFT with DMFT (DFT + DMFT) wave functions, which can be used to calculate DFT + DMFT wave-function-dependent quantities. We illustrate this by calculating the electron localization function (ELF) in monolayer SrVO 3 and CaFe 2 As 2 , which provides a means of visualizing their chemical bonds. Monolayer SrVO 3 ELFs are sensitive to the charge redistribution between the DFT, one-shot DFT + DMFT, and fully charge self-consistent DFT + DMFT calculations. In both tetragonal and collapsed tetragonal CaFe 2 As 2 phases, the ELF changes weakly with correlation-induced charge redistribution of the hybridized As p and Fe d states. Nonetheless, the interlayer As-As bond in the collapsed tetragonal structure is robust to the changes at and around the Fermi level.

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The Fermi surface topology plays an important role in the macroscopic properties of metals. It can be particularly sensitive to electron correlation, which appears to be especially significant for the weak itinerant ferromagnet ZrZn2. Here, we look at the differences in the predicted Fermi surface sheets of this metallic compound in its paramagnetic phase for both density functional theory (DFT) and the combination of DFT with dynamical mean field theory (DFT+DMFT). The theoretical spectral functions evaluated at the Fermi level were used along with calculations of the electron-positron momentum density (also known as the two-photon momenutm density) in k-space to provide insights into the origin of certain features of the Fermi surface topology. We compare this two photon momentum density to that extracted from the positron annihilation experimental data (Phys.Rev.Lett.92,107003 (2004)). The DFT+DMFT densities are in better agreement with the experiment than the DFT, particularly with regard to the flat bands around the L and W high symmetry points. The experimental neck around L, which relates to a van Hove singularity, is present in DFT+DMFT but not in the DFT. We find that these flat bands, and as such the Fermi surface topology, are sensitive to the many body electron correlation description, and show that the positron annihilation technique is able to probe this. This description is significant for the observed behavior such as the Lifshiftz transition around the quantum critical point.