Revisiting the magnetic ground states of RECo$_5$ permanent magnets

Abstract: In light of recent improvements in the theory of rare earth magnets, as well as the availability of improved neutron powder diffraction data on these materials, we revisit the magnetic single-ion properties of SmCo$_5$ and the magnetic structures of YCo$_5$ and NdCo$_5$. From neutron diffraction patterns in a wide range of temperatures between 3 K and 800 K, we obtain the thermal coefficient expansion and the magnetic moment values for the latter two materials. For SmCo$_5$, we fit existing neutron spectroscopy data with a model recently used for NdCo$_5$ to obtain the crystal field parameters, which are essential to determine the low-lying energy scales that set the Hamiltonian. Our results may trigger new experimental and theoretical studies towards a new route for the realization of permanent magnets.