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