  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.
