# Nature of the magnetic moment of cobalt in ordered FeCo alloy

## TL;DR

This study combines DFT and DMFT to analyze the magnetic behavior of cobalt in FeCo alloys, revealing the importance of local correlations in stabilizing magnetic moments.

## Contribution

It introduces a combined DFT+DMFT approach to understand cobalt magnetism in FeCo alloys, highlighting the role of local correlations and non-Fermi-liquid behavior.

## Key findings

- Cobalt magnetic moments depend on surrounding magnetic orientations.
- Local correlations are crucial for stabilizing cobalt moments.
- Spectral functions match experimental photoemission data.

## Abstract

The magnets are typically classified into Stoner and Heisenberg type, depending on the itinerant or localized nature of the constituent magnetic moments. In this work, we investigate theoretically the behaviour of the magnetic moments of iron and cobalt in their B2-ordered alloy. The results based on local spin density approximation (LSDA) for the density functional theory (DFT) suggest that the Co magnetic moment strongly depends on the directions of the surrounding magnetic moments, which usually indicates the Stoner-type mechanism of magnetism. This is consistent with the disordered local moment (DLM) picture of the paramagnetic state, where the magnetic moment of cobalt gets substantially suppressed. We argue that this is due to the lack of strong on-site electron correlations, which we take into account by employing a combination of DFT and dynamical mean-field theory (DMFT). Within LDA+DMFT, we find a substantial quasiparticle mass renormalization and a non Fermi-liquid behaviour of Fe-$3d$ orbitals. The resulting spectral functions are in very good agreement with measured spin-resolved photoemission spectra. Our results suggest that local correlations play an essential role in stabilizing a robust local moment on Co in the absence of magnetic order at high temperatures.