ANALYSIS OF THE CRYSTAL-FIELD LEVEL SPLITTINGS FOR TM3-TYPE COMPOUNDS( IN YBCO)

We have developed a procedure to fit the neutron inelasting scattering spectrum of Tm-doped YBa2Cu4O8. In our method, which could be of gene ral interest for problems involving the J = 6 multiplet in tetragonal or rhombic crystal field, we replace part of the original parameters a ppearing in the tetragonal part of the hamiltonian with new ones which act directly on selected features of the spectrum. This is done by in verting part of the eigenvalue equations. By using the new parametriza tion we can easily find a set of tetragonal parameters which fits well the low-resolution spectrum, and that we use as the starting point of a numerical fit including also the rhombic ones.