Comments and AddendaThe section Comments and Addenda is for short communications which are not appropriate for regular articles. It includes only the following types of communications: (I) Comments on papers previousLy published in The Physical Review or Physical Review Letters.(2) Addenda to papers previously published in The Physical Review or Physical Review Letters, in which the additional information abstract for information-retrieval purposes. Accepted manuscripts folio~the same publication schedule as articles in this journal, and page proofs are sent to authors.The spin-orientation diagram of Tb, "Dy"Fe2 is constructed by Fe Mossbauer measurements and compared with single-ion calculations. The 4f-crystal-field interaction dominates the magnetocrystalline anisotropy properties, though the presence of additional contributions to the magnetic anisotropy free energy is indicated.Nonmajor cubic symmetry axes of easy magnetization have been established in some mixed rareearth ternary R', , R', Fe~, " as well as in binary CeFe"' SmFe"' and HoFe, ' cubic Laves cornpounds. These unusual axes of magnetization were found to occur over a relatively broad temperature interval, within which the easy axis of magnetization n rotates continuously over a wide range of directions, usually from one major cubic axis to another. It was believed" that the appearance of unusual, or transition regions, in the spinorientation diagrams of the R, ,R, Fe, compounds, is due either to coexisting domains of different major-axis spin alignments, or to additional, noncubic anisotropies, besides that which arises from the 4f-crystal-field interaction. Recent calculations' have demonstrated that the single-ion model, applied to the rare-earth ion, accounts for unusual axes of easy magnetization within the framework of cubic symmetry. These calculations involved the diagonalization of the single-ion Hamiltonianwith the 4f-crystal-field interaction the only source of magnetocrystalline anisotropyfor n parallel to the three major cubic axes, as well as for other directions of n which were confined to the (110) and (100) planes. Using the eigenvalues of the single-ion Hamiltonian, the magnetocrystalline anisotropy free energy per ion F"(n, T) is calculated. For a ternary R, "R"Fe,compound F(x, n, T) =(1x)Fsx(n, T) + xF"a(n, T) .The easy direction of magnetization, of a given composition, at a given temperature, is that for which the free energy has its lowest value.We report "Fe Mossbauer-effect measurements that were made in order to reexamine and supplement the previously reported' spin-orientation diagram of the Tb, , Dy"Fe, system. The analysis of the present Mossbauer results of Tb, "Dy"Fe, follows a least-squares-fitting procedure which is described elsewhere, " and enables determination of the direction of n relative to the cubic-cell axes. The present study was prompted by the single-ion calculations, ' which revealed regions of unusual spin alignments in Tb, "Dy, Fe"at temperatures and compositions that have not been investigated be...

The magnetic anisotropy properties of "Fe-doped NdCo, and HoCo& were studied by means of Mossbauer spectroscopy in the 4.2-300 K temperature range. The experimental results indicate the presence of spin reorientations taking place at 43.5 and 16 K, for NdCo, and HoCo"respectively. Single-ion-model crystal-field calculations account for the experimental results and allow the determination of the crystal-field parameters.