Unusual [uuw]and [uv0]-type axes of easy magnetization have been observed in some cubic rare-earthiron Laves compounds. The presence of these directions of spontaneous magnetization can be accounted for, within the phenomenological treatment of the magnetic anisotropy, by including eighth-power direction-cosine terms in the power expansion of the magnetic anisotropy energy. It will also be shown that the single-ion model predicts the existence of these directions. The conditions imposed on the bulk magnetic anisotropy constants are derived. Typical values of these constants in rare-earth-iron Laves phases are calculated using the singleion model. of the magnetic anisotropy constants Kl K2 and K, for several RFe, compounds and show that K, is often of the same order of magnitude as Ky and K,. Section V includes a short discussion of some experimental results. 13 4006

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It is shown that the insulating oxide Fe 2 TiO s exhibits anisotropic (uniaxial) spin-glass behavior below 55 K 0 Extensive experimental results supporting this conclusion, including principal magnetic susceptibility, neutron scattering, ultrasonic, specific heat, and oriented single-crystal Mossbauer measurements, are described.

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...