Calculates the spin-only magnetic moment for a
        given species. Only supports transition metals.

        :param species: str or Species
        :param motif: "oct" or "tet"
        :param spin_state: "high" or "low"
        :return: spin-only magnetic moment in Bohr magnetons

def mu_so(species, motif, spin_state):
        """
        Calculates the spin-only magnetic moment for a
        given species. Only supports transition metals.

        :param species: str or Species
        :param motif: "oct" or "tet"
        :param spin_state: "high" or "low"
        :return: spin-only magnetic moment in Bohr magnetons
        """
        try:
            sp = get_el_sp(species)
            n = sp.get_crystal_field_spin(coordination=motif, spin_config=spin_state)
            # calculation spin-only magnetic moment for this number of unpaired spins
            return np.sqrt(n * (n + 2))
        except AttributeError:
            return None